Orwell Astronomical Society (Ipswich)

Maintenance Of The Tomline Refractor

This page details maintenance activities on the Tomline Refractor. Much of the information is sourced from the records of OASI [a], not in the public domain but available to members of the Society. A companion article details maintenance activities on the fabric of the observatory.

The Tomline Refractor (Martin Cook, 13 August 2025.)

The object glass (OG) of the Tomline Refractor is an achromatic doublet, of clear diameter 258 mm. A crown glass is positioned at the end of the telescope closer to the object under observation and a flint glass closer to the eyepiece. The gap between the two is circa 0.3 mm. The two-element design minimises spherical and chromatic aberrations. (Modern refractors usually employ three- or even four-element OGs to reduce aberrations still further.)

The Tomline Refractor was commissioned in 1874. At the time, English manufacturers could reliably produce lenses up to circa 150 mm in diameter, and the OG was therefore procured from the company Merz of Munich. The flint lens was ground in 1859 and the crown lens prior to 1842 [2014a]. Unfortunately, Merz did not figure the OG to the very highest standard and, in the 20^th Century, minor refiguring was undertaken.

The two lenses of the OG are mounted in a brass cell which is not hermetically sealed. Over a period of years, therefore, dust and spores can gradually accumulate between the inner surfaces of the lenses, compromising optical performance. When the telescope was commissioned, the observatory was heated by warm-air flues from the Turkish bath suite situated on the lower floors of the observatory, and this likely prevented problems associated with the ingress of moisture into the gap between the lenses. However, at some date after the death of Colonel Tomline in 1889, the Turkish bath suite ceased to be used and ultimately was removed, and the observatory languished unheated. Nowadays, the observatory suffers from damp during winter months and it is possible that capillary action associated with the narrow gap between the lenses exacerbates the ingress of moisture.

The Tomline Refractor is fitted with two periscopes which enable the observer to view the declination setting circle. Each periscope has an object glass around 60 mm in diameter, mounted in a brass housing in the form of a tube which in turn fits inside the outer tube of the periscope. The OG is a doublet, with separate crown and flint elements, installed 343 mm inside the top (mirror side) of the periscope.

The original RA drive for the Tomline Refractor was a magnificent piece of Victorian clockwork engineering powered by the descent of large weights down the hollow shell of the observatory tower. Two weights were employed, enabled continuous operation, the observer winding one weight while the other powered the mechanism. Speed control was achieved by means of a centrifugal governor. The output of the mechanism was coupled via a drive-shaft to a worm wheel which engaged with a large toothed, RA drive wheel at the base of the polar axis. The drive wheel had 1440 teeth and the nominal rate of rotation of the worm wheel was therefore one RPM (there are 1440 minutes in a day). See figures below.

The historical record shows that in the fifteen years between the commissioning of the telescope and the death of Colonel Tomline, the declination axis of the telescope malfunctioned twice, necessitating repairs by the makers of the instrument. In the early 1930s, Edward Howard Collinson (1903-90) used the observatory. He later described the telescope at this time as being in "fair condition" and there is no record of him expressing dissatisfaction with the condition of the OG. In 1936, the OG was examined by an optical specialist, who noted evidence that it had long been exposed to damp. In the 1950s, members of IDAS (Ipswich and District Astronomical Society) occasionally used the telescope: surviving records make no mention of problems with the OG. By 1969, when individuals who would later form OASI began to frequent the observatory, the facility was in a very poor state of repair, and damp was a major problem. From that date forward, the OG has required frequent cleaning. In modern times, the declination periscopes have also required occasional maintenance. The original clock drive appears to have been mistreated over the years and, in modern times, no longer functioned effectively. OASI therefore installed an electric drive system. The following is a summary of the historical record, in chronological order.

1878

In September 1878, the declination axis of the telescope jammed. Mr. Simms (of the Troughton & Simms company) dismounted the telescope and restored correct operation by removing rust from the bearings [1879a].

One can only imagine the reaction of Colonel Tomline on learning that his telescope, one of the finest in private ownership in the land, only four years after it had been commissioned, had been rendered inoperative by rust. A famously disputatious individual, the Colonel was unlikely to have been impressed by the news!

1889

On 01 July 1889, the declination axis of the telescope again jammed [1989a]. On 19 August, the telescope was dismounted and Mr Simms re-ground the axis to the bearing, restoring correct operation.

Unfortunately, on this occasion Colonel Tomline was unlikely to be much concerned by the malfunction of his telescope. By this time he was seriously incapacitated, and in fact died less than a week after the telescope failed.

1936

The first recorded inspection of the quality of the OG was in July 1936 by Dr D W H Steavenson [b] (1894–1975), commissioned by Messrs C Baker, scientific instrument manufacturers of 244 High Holborn, London, on behalf of the Orwell Park Estate office which, at the time, was attempting to dispose of the telescope. (Steavenson's report mentions an earlier investigation of astigmatism of the OG in 1930 but, unfortunately, no record of this survives.) His report is reproduced below:

Report on 10" Merz Objective, Tested 3^rd July 1936

General Condition

The material of the components is of good quality having regard to their age. They are free from chips, scratches, and harmful striae, and are of good polish, apart from some deterioration of the polish on the second surface (near surface of the crown lens) due to long exposure to damp. This slight cloudiness, which cannot be removed by cleaning, has no appreciable effect on performance. I have cleaned all four surfaces.

The three tin-foil spacers were found to be too thin, allowing of central contact of the components. They have been replaced by three spacers of adequate thickness. The cell is satisfactory except for the arrangement of double springs for maintaining centration of the components. This is a harmful system, no longer employed by the best makers, as it performs its function only by keeping the lenses under constant pressure. The springs have therefore been loosened, and the centration maintained by the insertion of paste-board packing.

Results of tests on artificial star

Colour Correction: This is satisfactory, but has been carried further than is usual in more modern objectives. It could be improved by an increase in the separation of the components.

Spherical Correction: This is satisfactory in general, but see under "Zonal Abberation".

Zonal Aberration: This is present in rather a marked degree. There are zones of short focus at radii of 1", 2" (the worst), 3" and 4". Also a central point of short focus.

Astigmatism: When the OG was first tested, as received, this was present in a marked degree, as had been noted by Orwell Park in 1930. On removing the lenses from their cells, they were found to be properly spaced, according to makers' own marks, and I think it almost certain that this astigmatism arose from a permanent distortion of the lenses, produced by long pressure of the spring side-support. Unfortunately one lens (the flint), is much more affected than the other so that complete balancing-out by rotation is impossible. But a considerable improvement has been obtained by rotating the flint through 40°, and new marks (signed W.H.S.) have been made at the edges. The old marks have been labelled but not removed. Some slight astigmatism still remains, but it is not serious enough to impair performance for general purposes.

General Conclusions

This is a serviceable old objective, though not one of the highest excellence. It gives excellent results with powers up to 150x, and satisfactory with medium powers (up to 300). But it is not capable of the most delicate work that a first class objective of its size should do. The aberrant zones throw too much light into the diffraction rings, and this would affect work on close unequal stars and would destroy contrast in fine planetary details. The glass is therefore unsuited to the more exacting work (research), but would do admirably for general demonstrations and instructional work, in some school or institution, where the extreme limits of performance under high powers were not called for.

Signed: W H Steavenson

circa 1970

The earliest surviving record relating to maintenance of the OG subsequent to the formation of OASI is a mention in the February 1973 Newsletter [1973a] that a Mr Wilton, formerly of Ipswich, had removed and cleaned the OG "some years" previously. It is likely that the work referred to was associated with initial renovation of the Observatory, but there are no further details.

1973

In January 1973, the committee of OASI investigated having the OG removed for cleaning, refiguring and general servicing by Horace Dall of Luton (the leading optical expert in the UK and vice-president of the BAA). Initial enquiries indicated that the work was within the modest means of the Society and the committee therefore decided to proceed and in fact arranged for Horace to overhaul also other optical components from the observatory. Accordingly, on 20 May 1973, members of OASI removed the OG from the Tomline Refractor and, on 22 May, Geoffrey Collier, OASI Treasurer, transported it to Horace together with the OG of the transit telescope and eyepieces for both instruments [1973b, 1973c, 1973d, 1973e, 1973f, 1973g].

On initial examination of the OG, Horace detailed the following problems:

• Bad over-correction for spherical aberration. Rays travelling through the centre of the lens arrived at a focal point separated by approximately one centimetre from the focal point of rays travelling through the edge of the lens. This discrepancy is about the same as the focal length of a high power eyepiece, and may have accounted for the poor performance of the telescope in splitting close double stars. Horace planned to correct this error by refiguring the lens, and to address some localised zones of poor figure (zonal aberrations) as part of the same correction.
• Chromatic aberration was very slightly over-corrected, but not sufficient to require corrective action.

Horace expected to finish work on the OG on 20 August, and the committee made plans to re-install it on 29 August.

While Horace was working on the OG, members of OASI attempted to adjust the declination circle of the Tomline Refractor, which had been 45° out of alignment for as long as anyone could remember. (It is tempting to speculate that the circle had been re-fitted incorrectly when the telescope declination bearing was repaired in 1889.) However, with the OG removed, the telescope was badly out of balance along the length of its tube and, in order to adjust the declination circle, it proved necessary to remove the massive lead counterweight on the other end of the declination axis from the telescope. When the counterweight was removed, there was a tense moment as the telescope, now severely unbalanced in both RA and Dec, started to slew rapidly and threatened to collide with other equipment or occupants in the dome! Everyone present scrambled to help control the rampaging instrument and fasten a system of ropes to hold it steady, enabling work to continue safely. Eventually, the declination circle was removed and refitted to show the correct reading.

Horace worked to the agreed schedule and members of OASI collected the OG on 26 August and duly re-installed it in the Tomline Refractor on 29 August. His reports on the micrometer eyepiece (June 1973) and the OG and various eyepieces (25 August 1973):

Remains of Merz Micrometer Eyepiece

Whilst I have tidied this wrecked/damaged instrument and replaced a few missing screws, there is so much damage & vital parts missing that I cannot consider restoring it.

The other work on the transit telescope optics is now complete.

Signed: H Dall, June 1973

Luton, August 25^th 1973. OASI Merz Refractor (1872).

f/15.1. Clear aperture 258 mm or 10.16". Focal length 3894 mm or 153.3".

Refigured by H Dall August 1973.

The zonal errors of spherical aberration as reported by Dr Steavenson in 1936 and confirmed by H E Dall in 1973 are now mostly removed. The two deep zones set in the central 4½" area are gone and the general over-correction of 0.243" is now removed. Astigmatism at the present orientation of the elements (not the same as found on receipt) is undetectable at steady temperatures. With good seeing conditions the instrument should now take high power eyepieces if desired.

6 eyepieces in wooden box have been cleaned and power measured as follows:

1. Large Ramsden, f = 2.05" = x75
2. Large Huygenian, f = 2.00" = x77
3. Huygenian, f = 0.90" = x170
4. Huygenian, f = 0.60" = x256
5. Huygenian, f = 0.374" = x410
6. Huygenian, f = 0.300" = x512

Signed: H Dall

Horace's failure to repair the micrometer eyepiece was not unexpected - when OASI first arrived at Orwell Park, members of the Society had found the eyepiece in a very poor state of repair, abandoned in a cupboard with an accompanying toffee paper!

In a letter to OASI committee member Charles Radley, on 20 August 1973, Horace explained why Steavenson had not noticed the over-correction of the OG for spherical aberration:

Dr Steavenson did not notice the spherical aberration over-correction because of two deep zones in a region which masked the error. The only aberrations left now are on a surface I have not worked on, and they are feeble, having no effect on performance. The zonal spherical errors originated in the Merz workshops, and have been there for 100 years or more.

In addition, during 1973 members of OASI beat out the large dew cap of the Tomline Refractor, restoring it to the correct shape [1973g].

The condition of the drive mechanism of the telescope greatly occupied the committee in the years that followed. However, the minutes of the 1973 AGM [1973h] simply note that the "automatic drive to the telescope" was functional. The ability to track objects in the night sky stimulated enthusiasm among members to experiment with long-exposure photography; to that end, Charles Radley organised the fabrication of adapters to enable the use of SLR cameras and members' eyepieces with the telescope [1973h]. Charles also proposed [1973i] purchasing a Barlow lens as a means of multiplying the range of effective focal lengths provided by the Society's stock of eyepieces. Late in the year [1973j], it was agreed to purchase a new 12.5 mm or 15 mm eyepiece.

1974

In early 1974, at the AGM, the committee [1974a] expressed interest in purchasing filters, an orthoscopic eyepiece of magnification x150 and possibly a Barlow lens. Unfortunately, in the short term it proved impossible to find a supplier with orthoscopic eyepieces in stock [1974b, 1974c]. In late summer, however, the committee [1974d] again expressed the intent to purchase an orthoscopic eyepiece of "medium range" and, by early autumn, the Chairman reported [1974e] that a 25 mm orthoscopic eyepiece was available for £12.04. The committee agreed to proceed, and the purchase was duly made [1975a]. To encourage use of the Tomline Refractor, in mid-1974, Tom Cardot sourced an adapter enabling use of modern eyepieces with the instrument [1974d].

Unfortunately, the RA drive mechanism had suffered through neglect and vandalism over the years. When OASI began regular use of the observatory, although the drive was functional, it was not reliable and required much maintenance and ongoing "tinkering". There was interest, therefore, in restoring or replacing the drive, to provide accurate tracking, thereby enabling the instrument to be used for long-exposure photography. In the middle of the year, investigations were ongoing into the possibility of fitting a replacement electric drive [1974d].

With the prospect of an improved RA drive, David Bearcroft requested that the committee invest in a high-magnification sighting telescope, to be mounted on the Tomline Refractor, to provide a means to check the accuracy of tracking. Some 11 years later, his wish was granted, and a guide telescope was fitted (see image below).

1975

At the AGM [1975a], the Chairman expressed interest in obtaining more eyepieces. Rising to the challenge, Tom Cardot subsequently donated two [1975b].

Also early in the year, the committee intended to refurbish the periscopes [1975c]. It is unclear whether the work was undertaken.

Owing to a frayed cable, the RA drive mechanism was out of action. A new cable was purchased and fitted [1975b]. Subsequently [1975d], it was noted that the telescope was "rather stiff to move" and should be eased, and there was renewed discussion about an electric drive. In fact, repairs to the RA drive mechanism were not without a humorous side, as the following report by David Bearcroft in the June edition of the Newsletter [1975e] illustrates:

We have not been idle. We have been in a battle to repair the telescope drive system. The work went not without incident when a member of my Tuesday night band, Mr D Barnard, was ordered below the floorboards to adjust the liner which carries the main drive weight. All went well, after much crawling around under the floor of the dome to the accompaniment of ribald remarks such as "spot the looney", "wonder mouse" and "super mole", until I advised him that there were probably spiders, termites and bats sharing the space under the boards. Our hero decided that enough was enough and tried to exit via the air vent through which he entered the space. Unfortunately, he became stuck and, after much pulling and pushing, we decided that an arm would have to be removed. Our hero did not like this idea a lot, nor the idea of leaving him there and feeding him once a week. Aided by three other people, we managed eventually to extract him in one piece. Still, it was all in a good cause for the clock drive is now back in operation and running better than ever.

1976

By 1976, the eyepieces and OG were in need of cleaning once more. Members present at the AGM in early January [1976a] suggested engaging Horace Dall again to clean the optics and to purchase a new set of eypieces; the matters were remitted for discussion by the committee. By early spring, eschewing the opportunity to give the work to Horace, committee member David Bearcroft had cleaned the eyepieces and the OG [1976b, 1976c].

The limitations of the clockwork RA drive were, by this time, painfully apparent, and at the year's AGM [1976a], the Chairman noted that an electric drive would be required before serious photographic work could be undertaken and a photographic section of OASI formed. During the year, some progress was made towards an electric drive, and a motor was obtained, but there was no obvious means of coupling it to the telescope; indeed, the committee envisaged a mechanism of gears, which would need to be specially cut [1977a].

In the meantime, experimentation with prime focus photography (using the telescope as a giant telephoto lens for a camera) revealed that, in this mode of operation, the draw tube of the telescope could not be retracted sufficiently to achieve focus. Fortunately, the committee eschewed the sacrilege of cutting the draw tube to shorten it and instead considered use of a Barlow lens to provide greater back-focus [1976d]. The matter appears to have been resolved somehow without either cutting or use of a Barlow lens, and the committee commissioned fabrication of an adapter which would screw into the draw tube and provide a Pentax thread for attaching a camera body [1976e]; originally, it was hoped that Mr Hazelwood, the father of a member of the Society, would be able to fabricate the adapter, but it is unclear whether he ultimately did so. The adapter took several months to fabricate [1976f, 1976g, 1976h] and was finally ready by the end of the year [1976i].

In order to increase the range of eyepieces which could be used with the telescope, the committee investigated commercial availability of an adapter for Japanese eyepieces (originally thought to be of diameter 1.25"; later found to be of diameter 1.5") and a suitable adapter was costed at £7 [1976f, 1976g, 1976h]. It is unclear when or even whether such an adapter was eventually purchased.

Imperial College, London, donated six eyepieces and a Barlow lens to OASI during the year. Charles Radley wrote on behalf of the committee formally thanking the College for its generosity [1976h].

Also, acting on the desire of members expressed at the AGM, the committee considered investing in a set of good quality eyepieces for use with the telescope [1976i].

1977

Unfortunately, the cleaning of the OG in 1976 did not have lasting benefit and, by early 1977, once more moisture and dust had settled between the two inner surfaces of the lenses and an area of dirt was visible. The committee therefore arranged again to transport the OG to Horace Dall so that he could dismantle the doublet and clean and refigure the inner surfaces. The committee hoped that the work would extend the visual magnitude range of the instrument to 14.2 and improve image quality. Horace quoted and charged the sum of £25 for the work [1977b, 1977c, 1977d, 1978a].

Members of OASI removed the lens from the telescope on 03 March 1977 and David Bearcroft subsequently collected it from the observatory and delivered it to Horace in Luton. David returned to Luton to collect the lens on 18 March and members of OASI re-fitted it to the telescope tube on the following evening. The following photograph by Martin Cook shows the lens cell on 19 March 1977 on re-fitting. (Contrary to what appears in the photograph, written on the lens cell, 19 March 1977 was the date of refitting the lens, refiguring having been completed some days previously.)

The night of 19 March was perfectly clear and, after refitting the lens, the telescope was turned to the sky. The resolution and clarity of the instrument were much improved [1977e, 1978a]: Saturn's rings and the bands on Jupiter's disk were crystal clear and it was possible to resolve double stars with considerably more definition than previously. The results were so good that the members of OASI present found it hard to leave the observatory!

The long effort to construct an electric drive for the telescope continued, under the leadership of David Bearcroft, with Mike Barriskill addressing the problem of coupling the motor to the RA drive wheel and Alan Smith investigating a control unit [1977c, 1977f]. By spring, it became apparent that the motor obtained the previous year was not powerful enough for the intended purpose and the team considered again whether it would be feasible to restore and renovate the original weight-driven mechanism [1977d].

As usual, the committee was exercised by the matter of obtaining the best eyepieces it could afford, and David Bearcroft wrote to Horace Dall asking for his advice on the matter. There is no record of a reply.

Alan Smith achieved a notable first during the year by coupling a TV camera to the telescope [1977c].

1978

David Payne re-energised work on an electric drive [1978c]. There was considerable discussion of the considerations and options, and potential suppliers were contacted [1978k]. Later, various considerations were summarised in the Newsletter [1978m, 1979i]:

• Options to retain the original drive system and replace the centrifugal governor with a servo-based speed-control mechanism utilising strain gauges were considered but rejected as impractical. The general consensus was that even if OASI completely re-conditioned the drive, it would not achieve accuracy better than ±10%. The decision was therefore made to construct an electric drive system.
• There could be considerable friction in the overall drive train of the telescope, so a powerful motor would be required. A single powerful motor would be preferable to several small motors working in parallel.
• A variable frequency oscillator driving a synchronous AC motor would enable some adjustment of the drive speed around nominal sidereal rate, which could be useful to overcome tolerances in the nominal setting.
• A motor locked to mains frequency, which generally has a short-term accuracy of ±0.1%, would be suitable for visual observing but not astrophotography, due to the lack of rate adjustment.
• A DC drive motor with a rheostat for speed control would be unlikely to offer better than 5% accuracy.
• A stepper-motor of sufficient torque would likely be a good choice if not too expensive. Stepper motors can operate in very small steps at high frequency, providing an effectively continuous drive. Stepper motors generally have a wide range of operating speed and can be powered from a low-voltage DC supply, enabling back-up power to be provided in case of mains failure.
• If an oscillator were employed to drive either a synchronous motor or a stepper motor, it should be temperature-compensated. (The temperature stability of oscillators can sometimes leave scope for improvement.)

In early 1978, Alan Smith and colleagues constructed a mains-operated electric drive based on a variable frequency oscillator and squirrel-cage motor with integral gearbox [1978L, 1979i]. The motor was coupled via a flexible shaft and an original set of bevel gears to the worm wheel meshing with the main RA drive wheel. The torque transmitted to the RA drive wheel was much in excess of the 2.5 Nm required to turn the telescope. It was planned to fit a cover to the drive and gear-train for safety reasons. In use, the drive was generally rested after running continuously for up to an hour, in case of overheating (although in practice, this did not appear to be an issue). Testing on solar and stellar observations, running the drive for up to an hour, indicated that it ran slightly too fast, but within 2.5% of sidereal time [1978L]. This was adequate for visual observations, but less than ideal for long-duration photography.

The new electric drive was a very welcome enhancement to the capabilities of the telescope and stimulated renewed interest among members of the Society in using it. However, room for further improvement remained. The worm wheel could be disengaged from the RA drive wheel in order to allow free movement in RA for initial sighting of an object. Unfortunately, the 1440 teeth of the RA drive wheel provided limited resolution when re-engaging the drive, and could cause "jogging" of the image, enough to move a carefully-centred object out of the field of view at high magnification. The solution was to fit a limited-torque friction clutch, enabling adjustment of the telescope in RA without disengaging the worm wheel; this had the secondary benefit of protecting the teeth of the RA drive wheel from being stripped if there were any accidental sudden movement of the instrument.

In fact, the original drive had included just such a clutch mechanism, controlled from the eyepiece end of the telescope by a sequence of mechanical linkages. Unfortunately, the mechanism had suffered theft and vandalism over the years, as a result of which it no longer functioned and insufficiently much remained to enable it to be reconstructed with certainty. Although Alan Smith volunteered to attempt to restore the original mechanism [1978d], this course of action was not pursued and, instead, Martin Cook and David Payne began construction of a replacement. Unfortunately, after the new drive mechanism had been in use for some months, it became apparent that the telescope was not well-balanced [1978n], with the counterweight seemingly being too light, and polar alignment was suspected to be in need of adjustment [1978g, 1978i]. The declination manual adjustment was in need of repair [1978i] too at this time. Meanwhile, David considered the possibility of improving the new drive [1978d, 1978e, 1978f, 1978g].

In late 1978, a snowflake-like fungus developed on the OG, compromising by some three or four magnitudes the limiting magnitude of the telescope and diminishing its resolving power. The minutes of the committee's November meeting paint a particularly grim picture: OG very dirty. Also, something seems to be growing on the back surface of the front element. Roy Cheesman wrote to Horace Dall about the matter and once more arranged for him to clean the OG [1978i, 1978j].

In early 1978, the committee considered and rejected the idea of purchasing a wide-angle eyepiece for use with the telescope on the basis that the likely cost, circa £70, was excessive [1978b]. Later in the year, the committee agreed to purchase a 1.25" right-angle prism for use with the telescope, to make it easier to observe objects at high altitude [1978g]. A prism was subsequently purchased from Fullerscopes for £19.11 but was found to be useless, as it extended the optical path to such an extent that no eyepiece could achieve focus [1978h]. Fullerscopes agreed to exchange the prism for a 12 mm orthoscopic eyepiece with RAS thread; the eyepiece is believed to have arrived ultimately [1980a], but it took a long time, causing consternation to the committee [1978i, 1978j, 1979d, 1979e].

1979

Following correspondence with Horace Dall in late 1978, on 22 January 1979 the OG was removed from the Tomline Refractor and Secretary Mike Barriskill delivered it to Horace, who undertook a "while you wait" cleaning. The OG was refitted to the telescope on 25 January [1979a, 1979b, 1979c, 1979d, 1980a]. The refitting was timely as, at the AGM on 06 January 1979 [1979a], Mike described his intent to search for supernovae using the Tomeline Refractor. (There is no record that he ever found any.)

Horace [1979d] recommended installing a heating element to gently warm the OG to prevent further condensation. Members of OASI looked into potential solutions, including the use of a mains-powered wire heating element wrapped around the telescope tube at the position of the lens cell. Committee meeting minutes [1979e] concerning the proposed mains-powered heater note that the observatory would need to be locked while the heater was powered on and the facility unoccupied, to prevent the possibility of any unsuspecting visitor or member of the school staff being electrocuted! Ultimately, it took another 46 years before a heating element was fitted.

To correct the balance of the telescope, Roy Adams installed an adjustable counterweight, fitted via a flange on the declination axis [1979i, 1978j, 1979d, 1979e]. The new clutch mechanism was installed in mid-1979 [1979j]. Unlike the original, the new clutch had to be operated from the base of the polar axis, rather than the eyepiece end of the telescope (see image below).

By May 1979, David Payne had completed work on improvements to the electric drive, which he intended to install shortly [1979f]. By the middle of the following month, the improvements had been installed and were in service. However, under the improved system, the motor was coupled to the RA wheel of the telescope by means of a rubber disk acting as a flexible coupler; this was found to be unsatisfactory and David intended to replace it with a disk of nylon (or similar material). At the time, David was also working on an improved control unit [1979g, 1980a].

By June 1979, the committee had received another request to purchase a wide-angle eyepiece. This precipitated an effort to obtain prices for a variety of eyepieces, including the renewal of optics in existing low-power eyepieces [1979g, 1979h].

1980

Recognising the importance of the Orwell Park Refractor to the Society's activities, at the 1980 AGM, those present agreed a budget of £300 for the year on equipment including a wide-field eyepiece, books, astronomical charts and items for modifying the telescope [1980a]. Subsequently, the figure appears to have been reduced to £250 [1980d].

At its April 1980 meeting [1980b], the committee agreed to purchase a 40 mm FL Kellner eyepiece from H N Irving & Son (one of the last of the great telescope manufacturers from the golden age of British telescope making) for the sum of £12 + VAT, and to obtain a 32 mm FL Erfle eyepiece, of 50 mm external diameter, on trial from Bretmain Ltd of Felixstowe. The latter arrived during the summer and, after a short trial, was purchased for £77.96 [1980b, 1980c, 1981a].

At the same meeting, there was discussion of the dirty state of eyepieces in the observatory, the main cause being fingermarks left by visitors!

During its October meeting, the committee noted that of the £250 budgetted for equipment, astronomical charts and modifications to the refractor, only approximately £100 had been spent, and decided to spend the bulk of the remainder on a new electric drive system. David Payne was actioned to progress the work [1980d] and very conveniently estimated the cost of a stepper motor-based drive system as approximately £150, although he aimed to identify a cheaper system if possible [1980e].

At its November meeting, the committee noted that a second-hand gunsight had been purchased, for a sum of £9.50. The intent was to convert the item into a micrometer, and the committee authorised a further sum of £35 to purchase a Plössl eyepiece and Barlow lens for use with it [1980e].

1981

By early 1981, the Plössl eyepiece had been purchased [1981a]. Work on the micrometer eyepiece was continuing and it was intended to purchase a Barlow lens for use with it [1981c, 1981d], although the idea appears ultimately to have been dropped. Following further work [1981c, 1981d, 1981e, 1981f, 1981g], by August of the year the micrometer eyepiece was usable (although not completed for another year or so [1983b]).

Once more, there was a groundswell of opinion among members to purchase a low-power, wide-field eyepiece. The committee held the matter in abeyance pending further investigations [1980f, 1981a, 1981b].

During the year, David Payne led efforts to design "a more precise and sophisticated" new drive for the telescope, with support from Alan Smith and Martin Cook. The estimated cost had increased to £200 and commercial systems were under consideration. Ultimately, a new drive (see image below) was constructed rather than purchased, was installed by mid-year and was commissioned on 18 and 19 October 1981 (although the control unit required further development) [1981c, 1981d, 1981e, 1981f, 1981g, 1981h]. The new design was based on a stepper motor, thought to be superior for the application to a synchronous motor, and reduced the extent of the drive train required to transmit torque to the RA drive wheel. It also had the advantage that the rate of the stepper motor could be adjusted, enabling sidereal rate to be set exactly.

1982

Unfortunately, the telescope drive was found to have a periodic wobble in RA, of approximate amplitude 20 arcseconds, due to mechanical defects in the drive train. Although short photographs of bright objects (e.g. the Moon) were possible, the wobble prevented long exposure photography from being undertaken with the telescope. The committee undertook to investigate the matter [1982a, 1982c].

David Payne intended to complete work on the new control unit for the telescope drive during 1982, to make the drive easier to use [1982a]. However, little progress appears to have been made and, by the end of the year, the matter was still outstanding [1982f, 1982g].

Perhaps inspired by work on the telescope drive, in early 1982 there was discussion in the committee of the possibility of motorising the dome of the observatory (needless to say, the matter was not pursued!) and the trustees of the Society made a plea for members to undertake more "serious work" with the telescope [1982a]. To that end, committee member Mike Barriskill requested that the verniers be re-fitted to the RA drive wheel; unfortunately, some were in need of repair [1982b] and, ultimately, it appears that they were not fitted.

During the year, there was interest in the eyepieces available for use with the telescope. Treasurer Mike Nicholls tested a 12.5 mm orthoscopic eyepiece, which had always given poor images with the Orwell Park refractor, and found that it gave good results with his 200 mm reflector. The committee concluded that the eyepiece must have been optimised for use with short focal length instruments such as reflectors [1982d]. There was interest in obtaining a high power eyepiece for use with the telescope, and the committee made arrangements with R Hebbs [c] to bring a selection to the observatory for a trial [1982e, 1982f, 1982g, 1982h].

1983

During 1983, the telescope drive was finally completed [1983c, 1983d, 1983e]. Unfortunately, by mid-year, the hand control unit was in need of repair, which was undertaken after a few months [1983f, 1983g, 1983h, 1984a].

R Hebbs brought two high power eyepieces to the observatory, but they did not perform well. The committee suspected that the OG of the refractor was to blame [1983b].

After a period of four years, the OG was in need of cleaning once more [1983a] and arrangements were made to contact Horace Dall [1983b]. In the event, however, the OG was not cleaned until three years later.

Throughout the year, there was interest in repairing and refurbishing the periscopes of the refractor (used for viewing the declination setting circle). The committee engaged an M Brassington to repair the eyepiece-ends of the periscopes, and intended to arrange for committee member David Barnard to re-aluminise the mirrors [1983c, 1983d, 1983e, 1983f, 1983g, 1983h, 1983i].

During the March committee meeting [1983c], Chairman David Payne suggested purchasing a 100 mm OG to construct a guide telescope for the refractor. After contacting suppliers, by the end of the year the committee purchased a refractor with a 99 mm air-spaced OG at a cost of £230 [1983d, 1983e, 1983f, 1983g, 1983h, 1983i, 1984a].

1984

Early in the year, members of OASI fabricated mounting brackets to secure the guide telescope to the Tomline Refractor [1984b, 1984c]. However, in the immediate aftermath of being fitted, there is no record of the guide refractor being used.

Possibly inspired by the fitting of the guide refractor, committee member Nigel Gage suggested using the main refractor for photometry [1984b]. To help move forward the project, he proposed to arrange a lecture for members of OASI on the subject. However, there is no record of the telescope being used for photometry, nor of the lecture taking place.

Late in the year, the eyepieces for the periscopes were returned by M Brassington [1984d, 1984e]. The committee intended to complete restoration of the periscopes, but the project languished [1984f, 1984g] for the remainder of the year.

1985

Early in the year, almost a year after brackets were fabricated to mount the guide refractor to the main refractor, the committee noted that work on the task was complete [1985a].

During the year, after much delay, the periscope mirrors were recoated by a firm in Cambridge [1985a, 1985b, 1985c, 1985d, 1985e, 1985f], but the periscopes were not refitted to the telescope.

Towards the end of the year, the telescope mount had been lubricated [1985g] and a camera bracket installed on the telescope tube [1985h]. An additional counterwieght had been added to the declination axis to offset the weight of the guide telescope and any camera attached to the bracket [1985h]. Unfortunately, depending on the orientation of the telescope, operation of a camera mounted on it could require a cable release up to 4 m long; Martin Cook undertook a long-running attempt to source a suitable item [1986b, 1986c, 1987b].

Once more, the committee considered the potential purchase of a low power eyepiece [1985h].

As excitement grew over the return of Halley's Comet, Chairman David Payne encouraged use of the telescope as much as possible for observating the object [1985f].

In 1985, the long running project to refurbish the periscopes finally came to fruition [1985b, 1985c, 1985d, 1985e, 1985f]. Martin Cook and David Payne transported the mirrors from the periscopes (together with a mirror belonging to David) to Newmarket for re-aluminising [2024a]. Martin fabricated plain glass covers and holders for the top ends of the periscope tubes to stop the ingress of dust. By September [1985g], the mirrors had been re-aluminised, but the periscopes were not immediately re-installed on the Tomline Refractor.

1986

The Trustees of OASI became increasingly concerned at the delay to cleaning the OG (having initially requested the work three years previously!) and recommended that it be undertaken without further delay [1986a]. The committee noted [1986b] that established practice was to proceed with transportation and cleaning of the OG without specific insurance cover. In March, the committee made arrangements [1986c] to undertake the work in May but, in the appointed month, postponed the task to June [1986d]. On 11 June, members of OASI removed the lens cell from the Tomline Refractor and clamped it between 25 mm sheets of plywood for safe transportation to Chairman, David Payne, who cleaned it [1986e, 1987a]. The lens was refitted by early July [1986f] and subsequently remained undisturbed for almost a decade.

Almost 40 years later, David recounted [2024a] that while cleaning the OG, he found no trace of the paste-board inserted 50 years earlier by Dr Steavenson. It seems therefore that on a prior cleaning of the OG, the person concerned took the paste-board to be an unwanted ad hoc addition to the lens cell, and disposed of it.

The telescope drive and its electronic control circuit required attention, including replacement of the worm drive shaft, but work on this appears to have been largely delayed until subsequent years [1986b, 1986c, 1986f, 1986g, 1986h, 1986i].

OASI acquired several items of equipment during the year. Mike Harlow suggested the purchase of an illuminated eyepiece for use with the guide telescope [1986a, 1986b]. (During discussion, it was suggested that if a tripod were obtained too, the guide telescope could be dismounted from the Tomline Refractor and taken on field trips.) After several months of deliberation [1986c, 1986d], Mike ordered a 6 mm illuminated eyepiece which he subsequently modified to incorporate illuminated crosshairs, completing the work by the end of the year [1986f, 1986g, 1986h, 1986i, 1987a].

The committee also discussed several items of potentially useful equipment without proceeding to purchase:

• A suggestion at the AGM [1986a] to purchase a filar micrometer eyepiece appears not to have been pursued.
• Roy Gooding investigated purchase of a 75 mm Plössl eyepiece [1986b].
• Alan Smith aimed to obtain a video camera to provide a display of the view through the Tomline Refractor [1986b]. After several months, he reported on possible ways ahead, but the matter does not appear to have been taken further [1986c, 1986d, 1986f, 1986g].
• The committee discussed purchasing a filter to suppress light pollution [1986c] and identified two main options: a relatively large filter (approximately 75 mm in diameter) fitted inside the telescope draw tube, or a much smaller filter installed at the eyepiece. The committee asked member Colin Button, owner of a light pollution filter, to bring it to the observatory for a trial evening [1986d] and eventually concluded that the option of a large filter would be prohibitively expensive. Filters to suppress only sodium and mercury vapour lines (the main causes of light pollution at the time) turned out to be unavailable [1986g] and it appears that a filter was not ultimately purchased.

During the year, Astro Systems announced the intent to purchase selected items from the US in bulk for resale in the UK at discounted prices. OASI took out a £5 subscription with the company to receive early warning of items of potential interest. Chairman David Payne enquired with Astro Systems about the potential to purchase a wide-angle eyepiece [1986f] and duly placed an order for a model with 0.75° field of view, sufficient to capture the whole of the Moon [1986g, 1987a].

By the middle of the year, the eyepiece draw-tube had been cleaned and oiled [1986f]. By mid-summer, the periscopes, with re-coated mirrors (see above) had still not been reinstalled on the telescope [1986g].

Only one year after the refurbishment of the periscopes of the Tomline Refractor, the committee noted that one of them required unspecified repairs [1986g].

1987

Several lines of activity were initiated at the 1987 AGM [1987a]. The Chairman noted that the drive for the telescope was varying in speed and that a new control system was under construction. By spring, the control circuit had been modified but the motor was apt to stall and further investigation was required. (It was suspected that the worm drive shaft was out of alignment.) Unfortunately, little progress was made and the matter remained pending for much of the year [1987b, 1987c, 1987d, 1987e, 1987f].

Also at the AGM, the committee agreed to purchase an equatorial head for the guide telescope, enabling it to be used on field trips. After considering a Fullerscope Mk II mount [1987b] and consulting manufaturers' catalogues [1987c], the committee eventually allocated £137 for purchase of a unit, complete with drive gears and counterweights, from Ian Poyser [1987e, 1987f, 1987g]. At the 1988 AGM [1988a], the Chairman reinforced the intent to use the guide telescopes on field trips.

At the first committee meeting following the AGM [1987b], the Chairman suggested buying a filar micrometer eyepiece. Following discussion [1987c], it was hoped to purchase one at the Guildford Convention that year, but no suitable models were available, so the matter dragged on throughout the year [1987d, 1987e, 1987f, 1987g].

Early in the year, Martin Cook fabricated an adapter enabling the new wide-angle eyepiece to be used with the Tomline Refractor [1986h, 1986i, 1987b]. Martin also provided a lens cap for the guide telescope [1987b, 1987c].

Mike Harlow undertook unspecified repairs to one of the periscopes [1987c].

The committee agreed to purchase filters (green, red, yellow, polarising) for use with the Tomline Refractor [1987c]. However, in the event, filters were not purchased for another two years.

1988

During the year, members restored the original clock drive for the Tomline Refractor [1988b, 1988c, 1989a]. (The drive was not, however, re-connected to the telescope, which continued to benefit from an electric drive.)

Further work was pending on a periscope [1988b] which had developed a "sharp end" [1989a].

By the end of the year, the filters for use with the Tomline Refractor were still to be purchased. David Payne intended to purchase a set from Astro Systems [1988d].

1989

At the 1989 AGM [1989a], several maintenance items were noted:

• The Tomline Refractor needed cleaning and its moving parts lubricating. In the event, the work was not undertaken for another year.
• The telescope drive was once more in need of attention. When driven, the telescope exhibited a small periodic wobble that made long-exposure guiding difficult. The committee planned to investigate the matter to see if the wobble could be eliminated. Again, the work was not undertaken for another year.
• The OG (particularly its front surface) required cleaning. In the event, the OG was not cleaned during the year [1989b, 1989c, 1989d, 1989e, 1989f].
• The dew shield of the Tomline Refractor displayed several dents which needed to be beaten out. The work did not appear to be undertaken.
• One of the periscopes had developed a "very sharp end" which required attention.
• The lens cap of the Tomline Refractor had become excessively tight. It was loosened during the year [1990a].

David Payne eventually ordered the filters for use with the Tomline Refractor, at a cost of £54. In use, the filters were accommodated in the telescope by means of a 1" adapter [1989b, 1989c, 1989d, 1989e].

Following a recommendation in the trustees report [1989a], Alan Smith labelled the controls on the Tomline Refractor [1989b, 1989c, 1989d, 1990a].

By the end of the year, the two periscopes associated with the Tomline Refractor had been collimated. No further work was undertaken on the periscopes for two-and-a-half decades. The committee noted that to make the declination setting circle fully usable, lights were required to illuminate it [1989g].

1990

Although action was not taken to comply with the trustees' request in 1989 to clean the OG of the Tomline Refractor, the trustees noted in their report for 1990 [1990a] that the lens appeared no worse than at the start of the previous year. The OG was not cleaned during 1990 [1990d, 1991a].

At the AGM [1990a], the committee allocated a sum of £300 for the purchase of a set of eyepieces for use with the Tomline Refractor. The eyepieces were subject to considerable discussion, and the committee eventually agreed to purchase 6 mm, 10 mm, 15 mm and 20 mm orthoscopic models [1990a, 1990b, 1990c]. They were not, however, purchased during 1990 [1991a].

In early 1990, the committee organised rebalancing of the Tomline Refractor, lubrication of its moving parts, and repair of the drive mechanism [1990c, 1991a], maintenance activities which had been recommended over a year previously.

Lights were purchased to illuminate the declination scale read by the periscopes on the Tomline Refractor [1990c, 1990d] but final installation did not take place until the end of the following year.

Pete Richards purchased a block of aluminium which could be machined to fabricate eyepiece adaptors [1991a].

1991

Once more, at the AGM [1991a], he trustees renewed their request to clean the OG of the Tomline Refractor.

By late 1991, the committee finally purchased the long-awaited four new eyepieces [1991a, 1991b, 1991c, 1991d]. The expenditure represented the bulk of the total expenditure on equipment for the year which amounted to £170.26 [1992a].

During the year, the mechanism of the RA setting circle was restored as far as possible; the declination circle did not require restoration [1991c]. Both setting circles, however, were in need of cleaning [1991c, 1991d, 1991e]. Lights, controlled by pushbuttons mounted on the eyepiece end of the Tomline Refractor, were installed to illuminate the declination setting circle [1991e].

1992

For the first quarter of the year, the committee continued to note that both setting circles were in need of cleaning [1992b, 1992c]. There is no record of the work being undertaken.

By the middle of the year, the committee noted that the OG was again in need of cleaning, several eyepieces also required cleaning and that internal reflections in the telescope required investigation [1992d, 1992e, 1992f]. By late in the year, members of OASI removed the OG from the telescope, removed the elements of the doublet from the cell, and cleaned all the glass surfaces with isopropyl alcohol (IPA). Martin Cook captured the operation in the following photographs.

By the end of the year, work to clean the eyepieces and to investigate the source of internal reflections remained pending [1992g, 1993a].

The committee considered purchasing a CCD camera for use with the telescope [1992f, 1992g].

1993

At the 1993 AGM, the trustees [1993a] reported that, during cleaning of the OG, several scratches were apparent in the centre of the lens. They also noted that the lens cap for the telescope was "lopsided" and that eyepieces were stored in a "haphazard" manner.

The committee, at its first meeting of the year [1993b], noted that the eyepieces still needed cleaning, that the RA vernier scale had become dislodged and needed to be re-attached (see details below for 1994; initial thinking was that the scale needed to be replaced), and that it would be possible to fit a cross-hair in the hole on the south side of the telescope mount to ease the task of making a precise reading of the RA setting circle. By May of the year, some (not all) of the eyepieces had been cleaned. The other items remained pending into the following year [1993c, 1993d, 1993e, 1993f].

The committee discussed purchasing additional eyepieces, including a 15 mm or 18 mm model, and a Na (Sodium) filter [1993d]. OASI member Alan Smith offered to lend OASI his Na filter to try it with the telescope. A sum of up to £600 was allocated for purchase of a computer and eyepieces [1993e].

The committee discussed the possibility of upgrading the speed controller for the telescope drive. A handheld unit enabled the drive to bs started and stopped and its speed to be varied to match the rotation of the heavens. The unit was connected to the drive motor itself earth via a lengthy, coiled wire, which on occasion presented a trip hazard to observers in the dark. The committee considered upgrading the unit to enable an infra-red link rather than a physical connetion to the drive motor [1993e, 1993f] and the work was completed, by OASI member Ian Swann, by the end of the year [1994a].

1994

At the 1994 AGM [1994a], the trustees reported that the condition of the telescope was as good as it had been during their last inspection, one year previously.

At its first meeting of the year [1994b], the committee allocated a sum of £100 for purchase of new eyepieces. Throughout the year, the problem with the vernier for the RA scale remained ongoing, as did the aspiration to fit a cross-hair in the hole on the south side of the telescope mount to enable easy reading of the RA scale. The committee noted that a digital display of the RA of the telescope would be a useful addition; unfortunately, it required more than 30 years (see below) for such a display to be procured! See [1994b, 1994c, 1994d, 1994e, 1994f].

Ian Swann modified the infra-red controller for the telescope drive motor. By May of the year, the new unit had still not been used [1994b, 1994c]. Later, concerns were raised in committee that the wiring of the controller needed to be checked [1994d], and it was agreed to ask Ian to do so [1994e, 1994f]. By the end of the year, the work had been done and the new controller was in use [1995a].

1995

Imaging technology advanced rapidly in the early 1990s and, by the middle of the decade, high quality CCD cameras optimised for astronomical use were available at reasonable cost. Society member Ian Swann had visited the Centro de Observação Astronómica no Algarve (COAA) in the Algarve in mid-1994 and returned with some excellent images taken with a CCD camera that he designed and built. At the 1995 AGM [1995a], Chairman David Payne recommended that the committee consider purchasing a CCD camera. However, the recommendation fell on stony ground: over a year later, the matter finally made its way into the list of topics for consideration by the committee [1996c], but no discussion appears to have been held.

Once again, the OG and some eyepieces were in need of cleaning [1995b, 1995c, 1995d].

Two long-running activities were addressed [1995b, 1995c]. The scale of the RA vernier was finally reattached, and the notion of fitting a cross-hair in the hole on the south side of the telescope mount, to enable easy reading of the RA scale, was shelved.

1996

Although, as noted at the 1996 AGM [1996a], the OG was once more in need of cleaning, the task remained pending throughout the year.

The committee purchased three new eyepieces for use with the Tomline Refractor [1996b, 1996d].

1997

Nothing of note.

1998

At the 1998 AGM [1998a], the Trustees reported that the OG "looked cloudy", but no action appears to have ensued.

1999

Nothing of note.

2000

At the 2000 AGM [2000a], members present discussed the possibility of purchasing a 50 mm eyepiece for the Tomline Refractor. In subsequent weeks, Pete Richards created a list of all the eyepieces in the posession of OASI, detailing the focal length and magnification (when used with the Tomline Refractor) of each, following which James Appleton purchased four eyepieces: 31.75 mm eyepieces with focal lengths of 15, 20 and 25 mm and a 50 mm eyepiece with focal length also 50 mm [2000a, 2000b, 2000c, 2000]. Meanwhile, David Payne ordered a new storage box to keep the eyepieces safe at the observatory [2000c, 2000d].

Several eyepeices were in need of cleaning, and the committee decided to take advice from Barry Elam on how best to approach the task [2000d, 2000e].

Once again, the OG of the Tomline Refractor was in need of cleaning. Martin Cook repainted the instrument. The committee recognised that the RA drive of the instrument was in need of an overhaul. See [2000d, 2000e].

Martin Cook cleaned the RA mechanism of the Tomline Refractor.

2001

Cleaning of the OG of the Tomline Refractor remained pending throughout much of the year [2001a, 2001b, 2001c, 2001d]. Just prior to the open evenings in late Novemnber, the front surface of the lens was cleaned [2001e].

Barry Elam provided advice on cleaning eyepieces and volunteered to undertake the task [2001b, 2001c]. However, for reasons unknown he did not do so, and the committee later asked St. John Robinson to undertake the task [2001d, 2001e].

Investigation of the RA drive unit remained pending initially [2001b]. By mid-year, David Payne had investigated the system and concluded that the electronics associated with the infra-red (IR) controller had ceased to function and that, unfortunately, replacement parts were no longer available and a new controller would need to be built [2001c, 2001d, 2001e].

Meanwhile, Martin Cook intended to restore some of the parts used historically with the original weight-driven RA drive mechanism [2001c, 2001d, 2001e]. The parts in question are nowadays of largely historic significance, and do not interfere with the operation of the modern, electric RA drive.

2002

Many activities stalled and remained pending with little progress throughout the year [2002a, 2002b, 2002c, 2002d]. Specifically:

• The RA drive system was becoming increasingly erratic in operation. David Payne established that parts to construct a new IR controller could be sourced from RS or Maplin Electronic Supplies. Martin Cook purchased a replacement integrated circuit for the IR controller (despite initial indications in the previous year that replacement parts were no longer available), but construction of a new drive remained pending.
• Repairs to the historic RA drive mechanism also remained pending.
• Unfortunately, although the front surface of the OG of the Tomline Refractor was cleaned in late 2001 (see above), a more thorough cleaning was required. Materials were obtained (iospropyl alcohol, de-ionised water, cotton wool and lens-cleaning tissues) but the task remained pending.
• At the other end of the telescope, cleaning of the eyepieces also remained pending.

2003

The late Ken Goward, FRAS, became chairman of OASI in 2003 and re-energised activities in the Society, enabling progress on several stalled matters.

At long last, the OG of the Tomline Refractor was cleaned! On 13 February 2003, Martin Cook and David Payne removed the OG and, in the map room at the Observatory, began to clean it. They completed cleaning the task three days later and subsequently refitted the OG to the telescope [2003a, 2003b]. The following photographs by Martin capture the operation.

Paddy O'Sullivan, with assistance from St. John Robinson, began cleaning the eyepieces [2003a].

David Payne installed the replacement integrated circuit in the IR controller of the RA drive, but it did not improve matters. Meanwhile, Mike Whybray was working on a potential new radio controller to replace the IR unit. However, another school of thought, which ultimately won the day, was to replace the drive unit in its entirety [2003c, 2003d, 2003e].

Paddy O'Sullivan and Martin Cook purchased a 50 mm eyepiece for use with the the Tomline Refractor [2003a, 2003c].

2004

Nothing of note.

2005

In April, the committee considered purchasing a webcam for use with the Tomline Refractor [2006a, 2005a]. However, at its September meeting, the idea was shelved [2005b].

Once again, the OG of the Tomline Refractor was in need of cleaning. Martin Cook undertook the work [2005b, 2005c].

In early November, Martin Cook noticed that the rack & pinion focusser of the Tomline Refractor appeared to be damaged, as is a section of teeth had been stripped from the rack [2005c].

2006

Although in late 2005 the committee shelved the idea of purchasing a webcam for use with the Tomline Refractor, at the 2006 AGM [2006a], a "CCD imager" was placed on the acquisitions list and, at its first meeting of the year, the committee noted among potential items of expenditure, purchase of a "webcam and equipment for CCD imaging" [2006b];. However, no such purchases were made during the year and, at the following year's AGM [2007a], they did not feature on the updated acquisitions list.

A new member of OASI stepped forward to construct a new rack and pinion focusser for the Tomline Refractor, to replace the original mechanism which was malfunctioning [2006b]. However, by mid-year, a repair had been effected to the original mechanism [2006c] so a replacement turned out not to be necessary.

2007

Paul Whiting purchased, for use with the Tomline Refractor, three 31.7 mm filters (Hα, Hβ and OIII) and a 50 mm 2x Barlow lens [2007b, 2007c].

2008

At the 2008 AGM [2008a], the Trustees reported that the lens hood of the Tomline Refractor had been badly dented in a collision with the wheel used to rotate the dome; they recommended that users of the telescope exercise more care!

In early 2008, Neil Morley purchased from Green Witch, Cambridge, two orthoscopic eyepieces (9 and 18 mm) for use with the Tomline Refractor [2008b].

2009

The Trustees reported at the 2009 AGM [2009a] that, once again, the OG of the Tomline Refractor was in need of cleaning. However, no action ensued from the report.

For several years, the electric drive motor (installed in 1981) for the Tomline Refractor had been unreliable. The problem was traced ultimately to a hairline crack in the motor drive board. In early 2009, the handle of the RA clutch broke and this catalysed an overhaul of the entire drive mechanism. Martin Cook and James Appleton fitted a new handle to the RA clutch and fabricated a new electric drive. The new drive benefitted from a more powerful stepper motor, all-digital operation and adjustment of RA drive speed via an FM handheld controller rather than a cable-linked unit, the cable of which had often proved to be a trip-hazard in the dark of the dome. However, the new drive retained the original gearbox (an antique salvaged from a WW I gunsight). The total cost of the new drive was £318.17 [2009b, 2009c, 2009d]. The figure below shows the new drive mechanism with its cover open.

2010

The Trustees repeated their observation made at the previous year's AGM that the OG of the Tomline Refractor was in need of cleaning [2010a]. Again, no action ensued from the report.

2011

For a third successive year, the Trustees reported at the AGM that the OG of the Tomline Refractor was in need of cleaning [2011a] and, also for a third successive year, no action ensued from the report. They also recommended that the bearings of the telescope be lubricated.

2012

For a fourth successive year, the Trustees reported at the AGM that the OG of the Tomline Refractor was in need of cleaning [2012a]. On this occasion, the committee responded with alacrity and made plans to remove the OG from the telescope and have it professionally assessed and cleaned by Es Reid of Cambridge. (Es is effectively successor to Horace Dall who, sadly, died in 1986.) One of the motivations was to obtain from Es an optical specification of the OG, which would enable consideration of whether it could be replaced by a modern lens, of much superior optical quality. (If the original OG were to be replaced, the committee would arrange for it to be placed in long-term secure storage so that it could be reinserted in the telescope at a later date to restore historical authenticity.)

Chairman Neil Morley obtained a quote of £250 from Es for the work [2012b], and made arrangements to remove the OG in late July, during the summer "maintenance period", when the telescope was out of action and the floor of the equatorial room was scheduled to be sanded and re-varnished [2012a]. Having confirmed with the Headmaster of Orwell Park School that the school insurance policy would cover removal, transportation and cleaning of the OG, it was duly removed from the refractor on 25 July and, on 28 July, Neil delivered it by car to Es. On 04 August, Es began work and, in the following days, performed several tests, thoroughly cleaned the lenses, re-polished the flat rear surface which seemed to be responsible for most of the zonal aberrations, and refigured the surfaces to a much smoother and flatter wavefront than before. Extracts from Es' reports on the work:

Put the lens on an auto-collimation test about an hour ago and first looks suggest a somewhat lumpy, zoney wavefront with the expected level of colour and quite a lot of scatter.

Tested [the OG] as supplied. The three large spacers lined up with the small amount of astigmatism so replacing those with six will reduce that effect.

It doesn't look mouldy, just a fine film of dust over each surface but I'll take a closer look to see if I can work out what it might be.

I've been really active this weekend and am re-polishing the flat rear surface [the surface of the flint glass facing inside the telescope tube] which seemed to carry most of the zonal aberrations. The cell is very well made of bronze and brass and fits together very smoothly - I shall give each part a hot water wash to de-gunge the surfaces. The lead spacers are fine in thickness but I will cut each in two and redistribute them.

I’ve worked for four days blasting away at the OG and it's back together, cleaner and refigured to a much smoother and flatter wavefront than before. There are some small, deep erosion pits on the inside surface of the flint plus some old scratches but there seemed little point in risking the objective to grind and polish them out. I hope that the six spacers keep the airgap more stable. There is some residual multiple astigmatism that may be from any of the surfaces and might be due to glass inhomogeneities, but it’s not severe.

This OG is the best I've seen of its size from so long ago when glass technology was trial and error.

Es also reported a patch of deterioration, due to mould inside the air gap, affecting the front (sky-facing) surface of the flint glass, but didn't believe it warranted repolishing the entire surface. He reported that the quality of the flint and cell assembly were among the best that he'd seen from the period. The OG was a perfect fit inside the inner cell (stamped Merz); the outer cell looked like a naval phosphor bronze bearing and was extremely well machined - he wondered if this could have been the work of Ransomes… Es' final bill amounted to a very reasonable £220 [2013a] and he recommended that the OG be removed and cleaned every five years [2012d].

While the OG was out of the telescope tube, members of OASI took the opportunity to spray-paint the inside of the tube matt black, to minimise internal reflections (thus finally addressing a matter originally aired in 1992 - see above).

On 12 September 2012, after servicing and refiguring by Es, the OG was refitted to the telescope tube. On inspecting the OG prior to refitting, Martin Cook and James Appleton noted that it still appeared cloudy, although less so than before Es had worked on it [2012d].

Photographs illustrating aspects of the work:

Other maintenance activities were carried out during the year too:

• Martin Cook greased the main bearings of the Tomline Refractor [2012c], as recommended by the Trustees during the previous year's AGM [2011a].
• There were further problems with the rack & pinion focusser of the instrument and Martin removed the mechanism for repair [2012b].
• During a visit to the observatory on 27 September, the electric RA drive was found to be non-functioning [2012d]. James Appleton and Martin Cook investigated.

2013

Unfortunately, all Es' hard work in 2012 did not have lasting benefit and, after only a few weeks, observers noticed that the definition of the telescope appeared to be compromised. Indeed, the Trustees, in their annual report to the 2013 AGM [2013a], commented on the fact. On investigation, the cause was found to be mist on the inner surfaces of the two lenses of the OG. The appearance of mist so soon after the lens had been cleaned was both disappointing and surprising, and was ascribed to a prolonged period of damp weather, with moisture likely condensing inside the telescope tube on the cold of the lens cell and being drawn by capillary action into the gap between the two lenses.

Es suggested possible approaches to dry the air inside the telescope tube, including an electric tape heater around the lens cell, a system to maintain air movement through the telescope tube and the use of zeolite to absorb moisture. Following considerable discussion, Martin Cook and Alan Smith constructed a bespoke de-humidifier for the telescope, using a large (empty!) mayonnaise tub, two flexible hoses and a fan salvaged from a surplus PC! The fan drew air from the telescope tube via a side vent, sent it to the tub, which was filled with silica gel, then returned it to the telescope via the eyepiece tube. The silica gel was removed and baked dry weekly. See the photograph below. The de-humidifier was fitted on 05 April 2013 and, after running for a week, had removed approximately 100 g of water [2013b]. After several further weeks of operation, the mist inside the OG appeared to diminish and it was hoped, as of early 2014, that the problem had been resolved.

2014

Again, the Trustees in their annual report to the AGM [2014b] noted that the OG of the Tomline Refractor appeared misty. The committee took no action, hoping that the dehumidifier, installed in the previous year, would ultimately resolve the problem.

Mike Whybray rebuilt the system of illuminators for the declination setting circle [2014c]. When doing so, he noticed that one periscope was missing an eyepiece (it was being used with the transit telescope), so he sourced a new one [2014d, 2016a]. It then became apparent that the declination scale moved slightly as the telescope was moved, so further investigations were undertaken.

2015

At the 2015 AGM [2015a], the Trustees reported being astounded to find, during their recent annual inspection of the observatory, that the RA drive wheel and worm gear of the Tomline Refractor were unlubricated. They advised application of a non-polluting lubricant. The observation by the Trustees was surprising as the RA drive wheel and worm gear had run dry satisfactorily ever since anyone could remember. Martin Cook advised that he periodically lubricates the RA drive wheel with a dry spray that avoids dust gathering on the gear teeth [2016a]. The Trustees also reported that the OG was "rather misty" and recommended that "a gentle wipe could help on occasions". Given the problematic and elongated history of efforts to maintain the OG free from mist, the Trustees recommendation of an occasional gentle wipe as an adequate remedy too elicited some surprise.

Mike Whybray effected a repair to the illuminator for the declination setting circle and, while doing so, found the periscope mirrors to be misaligned and loose. Together with Martin Cook, he renovated and tightened the mirrors and realigned the periscopes [2015b, 2015c, 2015d, 2015e].

At the International Astronomy Fair in October, Chairman David Murton talked with representatives of AWR Technology about the potential to fit a "push-to" mechanism to the Tomline Refractor. (A "push-to" is essentially a digital readout of the celestial coordinates to which the telescope is pointed.) AWR Technology specialises in fitting "push-to" and "go-to" mechanisms to historic telescopes and has done so at Greenwich and Herstmonceux. An initial guesstimate of the cost was £1500-£2000. The committee discussed the matter and Martin Cook began further investigations, contacting Alan Buckman at AWR Technology [2015e, 2016a].

The committee asked Bill Barton to purchase a star diagonal by APM Telescopes for use with the Tomline Refractor [2016b].

2016

At the 2016 AGM [2016a], in a break from the ritual of previous years, the Trustees reported that the OG of the Tomline Refractor looked clean! This enouraged confidence that the dehumdifier was performing its function.

Martin Cook reported that, following an initial dialogue with AWR Technology, the cost of a "push-to" system for the Tomline Refractor was now estimated at approximately £2500 [2016b] and that dealing with the company was hard work [2016c]! He began exploring cheaper, DIY options [2017a].

Martin also recalibrated the setting circles of the Tomline Refractor, enabling objects to be located without star-hopping.

2017

At the 2017 AGM [2017a], the Trustees reported that the OG of the Tomline Refractor looked a little cloudy.

At the same meeting, the committee added a "push-to" system for the Tomline Refractor to the acquisitions list, with a notional budget of "maybe a few hundred pounds". Later, Adam Honeybell, a software engineer, proposed fitting shaft encoders to the axes of the Tomline Refractor and writing software to create a DIY "push-to" system. Together with Martin Cook, he purchased shaft encoders (at a cost of only £14 [2017b]), mounted them on the Tomline Refractor and began developing software. By mid-year, a prototype system was functioning and the pair were concentrating on improving its accuracy [2017c].

2018

Work by Adam on the DIY "push-to" system continued into 2018 [2018a, 2018b]. John Wainwright purchased an Android tablet to work with the system in the equatorial dome [2018c, 2019a].

2019

Although the de-humidifier had been regularly in use in the equatorial room since 2013, it appeared to be unable to dry the air sufficiently and, in April, John Wainwright reported that the OG of the Tomline Refractor was very opaque and in need of cleaning [2019b]. With OASI running a full programme of visits to the Observatory, it proved impossible to find a date for the work [2019c, 2019d, 2019e].

2020

Eventually, during the Christmas holidays 2019-20, it proved possible to find an opportunity to remove the OG of the Tomline Refractor and Martin Cook then cleaned it. The LH image below shows the lenses of the OG immediately after cleaning: note the clarity of text of the Radio Times visible through the glass! Subsequently, on 29 January 2020 [2024b], Alan Smith and Andy Gibbs refitted the OG to the Tomline Refractor. The middle image shows the OG being unpacked in the observatory, immediately prior to refitting. Unfortunately, on refitting, the OG misted almost immediately [2020b] (see RH image), so the de-humidifier was again pressed into operation.

The Trustees report to the 2020 AGM [2020a] noted that the OG of the Tomline Refractor had recently been reinstalled and was already suffering from damp.

Progress on the DIY "push-to" system had slowed considerably due to a change in circumstances of Adam. Partly in response, Martin followed posts on the Cloudy Nights astronomy forum by Speo (forum username), who had developed a system like Adam’s and was hoping for commercial sales.

2021

The Trustees report to the 2021 AGM [2021a] noted that the OG of the Tomline Refractor was cloudy due to the ingress of mould.

Following the COVID-19 pandemic, there was concern that sharing telescope eyepieces could transmit the infection between individuals. In September, the committee of OASI discussed the matter [2021b] and decided to prevent the spread of infection in this way during visits to the observatory by using a camera to display the image from the Tomline Refractor on a screen, rather than have visitors peer through an eyepiece. The committee therefore agreed to trial Martin Cook's ZWO ASI178mm camera with the Tomline Refractor and, if all went well, to purchase a colour model (ASI178mc). The trial did indeed go well and a colour camera was duly purchased [2021c]. Almost 30 years had elapsed since the committee first discussed purchase of CCD camera for use with the telescope!

The committee discussed the state of the OG of the Tomline Regractor, which was desparately in need of cleaning once more [2021c]. It was thought that the separation between the elements of the lens was implicated in the problems and, if it could be increased, capillary action might be diminished. The committee made plans to remove and clean the OG over the Christmas holiday but, in the event, this did not happen.

In January 2021, in a change of heart, Speo posted full details of his project on Cloudy Nights, free for use by self-builders. Martin ordered the necessary parts to build a prototype on a piece of PCB stripboard and tested it with a couple of encoders. All worked well so he then ordered five custom-made PCBs from China (Speo had produced a set of drawings to facilitate PCB manufacture), with express delivery, for less than £20!

2022

At the 2022 AGM [2022a], the committee noted that the OG of the Tomline Refractor was still badly misted and that a premanently-running dew heater would probably be required to address matters. However, following a long, dry period over the summer months, the mist had diminished and the telescope was performing well [2022d]. The committee put on hold further cleaning of the OG until at least the end of 2023.

Following the success of the prototype "push-to" system, Martin and Adam worked to install the system on the Tomline Refractor. By February, the system was all but ready, and just required some tidying of cables [2022b]. By May, it was fully operational, and enabled objects to be located with ease [2022c, 2023a]. The total cost was under £100.

2023

The Trustees' report at the 2023 AGM [2023a] noted that the OG of the Tomline Refractor was cloudy and in need of cleaning. When Es Reid had cleaned the OG in 2012, he had reduced the thickness of the spacers defining the sparation between the two lenses. Following much informal discussion, the committee had increasing confidence that this could have increased the capillary action between the two lenses, thereby increasing the propensity for moisture to be drawn into the gap between them. The obvious solution therefore was to reinstate the gap to its original specification [2023b] and to construct a means of gently heating the OG, e.g. via a dew heater strip [2023c].

In October, Martin Cook removed the OG once more, cleaned and refitted it [2023c]. The following image shows the OG immediately before cleaning in October.

In December, he again removed the OG, cleaned it, increased the width of the spacers defining the size of the air gap separating the elements, and refitted it.

John Wainwright and Martin Cook experimented with dew heater strips on the Tomline Refractor, trying to find a way to route the associated (low voltage) power cables that would not be fouled on the telescope mount [2023c].

2024

Despite a very damp winter 2023-24, the adjustment in December 2023 to the spacing of the lenses appeared to have largely, but not completely, resolved the problem of misting [2024d]. Nevertheless, Trustee Neil Morley contacted Es Reid to discuss cleaning the OG and investigating in detail the optimum spacing of the lenses [2024c]; the committee agreed to proceed with work [2024d, 2024e]. Accordingly, on 10 July, Martin Cook removed the OG from the telescope and the following day, he and Neil transported it by car to Es. Later in the day, Es reported The lens is on test now with the 12" collimator and shows pretty good correction and lack of coma and colour, so you must have got the spacers about right… Es found the thickness of the six spacers between the lenses to vary between 0.29 and 0.36 mm, and adjusted them all to 0.29 mm: Spacers: 0.29 mm gives minimal longitudinal spherical aberration (LSA); any thicker and the objective will be under-corrected. LSA varies with wavelength so the assessment is rather subjective but the colour correction is very good and allows a pretty accurate judgment.

Es's overall summary of the lens: WHS's [Stevenson's] report rings true even now: there is a low level of triple astigmatism, best seen in blue light, that is not readily seen at focus. Considering that the lens is 150 years old, it works very well and the glass quality [is] extremely good for that time and aperture, but it's not perfect and there may be slight strain that causes the astigmatism… I can't improve it further - fine adjustment on site may tighten up the image.

The original system for suspension and centration of the lenses of the OG inside the cell comprised two fixed lead cushions and a third floating support tensioned via the use of paired carbon steel springs. The system provided three supports, spaced at 120° intervals around the circumference of the OG. While adjusting one of the springs responsible for tensioning the floating support, it snapped. (The carbon steel was "glass hard".) Es added an additional, fixed, lead cushion to hold the lenses in place, rather than the floating support, allowing them a minute amount of movement so that they are not under tension. He commented that the use of springs was rather archaic and was quickly superseded by the use of fixed cushions spaced at 120° intervals.

The following week, Es took the fractured spring to the Welding Institute for repair. Although the repair was effected to a very high standard, the floating support for the lenses has now been permanently retired, and the spring will not be refitted.

On 24 July, Martin and Neil collected the OG and, the following day, Martin re-fitted it.

Work also began to fit a dew heater on the Tomline Refractor, to keep the OG slightly warm and, it was hoped, free from moisture [2024f].

After a gap of almost a decade since the last maintenance on the periscopes, on 03 July 2024, Martin Cook and Neil Morley removed the top periscope for cleaning. On initial inspection, they found the OG to be covered with dirt and grime. It seemed that the glass cover at the end of the tube, fitted by Martin in 1985, was not fully effective in preventing the ingress of dirt, and that the situation could be improved by the addition of a gasket to ensure a good seal: at the time of writing, this possibility remains under consideration.

After some three hours work, it proved possible to extract the OG brass housing from the outer tube of the periscope. With the OG retaining ring removed, it was still a struggle to remove the OG from its housing due to internal threads in the latter being slightly raised. Once the OG was removed from its housing, it proved impossible to separate the elements for cleaning. Forced disassembly would risk destroying the three foil shims defining the air gap between the elements. The shims are likely cemented to the inside glass surfaces. Therefore, only the the outside surfaces of the OG could be cleaned. Martin provided a small plastic tub and some neat isopropyl alcohol (IPA). Neil cleaned the outside surfaces of the OG by hand then followed this up with Zeiss cleaning wipes (also containing IPA). During cleaning, some IPA entered the air gap between the elements and capillary action occurred, entirely filling the air gap with IPA; in fact, this was beneficial and likely lifted dirt from the inside surfaces. An air-line inflated to ~2.8 bar expelled the IPA.

Following cleaning of the brass housing, reassembly proved to be a lot easier, although great care was required as the fit is tight! Previous attempts, possibly using greater force, might have caused the small chips at the edges of the OG lenses (fortunately, these don't affect performance). Neil and Martin adopted the technique of taking a clean lens wipe and tapping it gently around the circumference of the OG to push the latter downwards inside its housing. A small amount of pressure on the outside of the housing helped. The housing for the OG is a friction fig inside the periscope tube. There is no mechanical stop inside the latter to locate the housing: instead the housing must be pushed down carefully until it sits at the correct depth. To that end, Martin fabricated a wooden "ramrod" with a depth marker at 343 mm, and used it to locate the housing correctly.

The periscope was refitted on 10 July.

Photos by Martin and Neil are below.

2025

A dew heater was finally fitted to the Tomline Refractor on 11 August, during the summer maintenance week. At the time of writing, the power supply remains to be wired in. More than 46 years have elapsed since Horace Dall first suggested the approach as a remedy to the seemingly never-ending problem of the OG becoming cloudy!

The image below shows the newly-installed wiring to the dew heater. Two heating elements are mounted inside the lens cap adjacent to the OG and a black junction box, mounted on the exterior of the telescope tube, connects to the blue cable which links to the power supply (to be installed).

Connection to the dew heater. (James Appleton, 12 August 2025.)

References

Footnotes

James Appleton, Martin Cook, Ken Goward, FRAS, Neil Morley

Updated: 04 September 2025