Orwell Astronomical Society (Ipswich)

Home Events

30 cm Prime Focus Reflector

The parts for my latest telescope have been around for years! I made the 30 cm mirror way back in the early 1980s and the "tube" assembly is based on a design illustrated in the 1976 Yearbook of Astronomy. (Thanks are due to Martin Cook for providing the aluminium poles which enabled me to rebuild it.) The design dispenses with the secondary mirror so it is purely a "camera" or prime focus reflector. In the photo below, a laser collimator is placed in the focuser where the CCD (Starlight Xpress MX916) normally sits on a heavy-duty spider. Dispensing with the secondary adds an extra 10% or so to the light gathering power but more significantly for me makes collimation much easier. Incidentally, the little blue tube on the side of the main instrument is the refurbished 11 cm telescope that was at the observatory for many years: it’s a perfect finder given that it isn’t possible to look through the main instrument.

They say that it’s difficult to take a bad image of M51 so it seemed like the ideal target to test the newly built telescope. The image below is a stack of thirteen 20 second exposures liberally stretched and shown as a negative. Two other galaxies (presumably more distant) also appear (with IC numbers added for identification).

The image of M108 is a stack of twenty-five 20 second exposures processed in a similar way. More distant galaxies pop into view this time (identified by PGC numbers). To give some idea of what can be detected with this set-up, PGC 34128 is listed as magnitude 16.

On the night of 21 August 2009, Tom Boles discovered another three supernovae, bringing his total to 124! One of the new discoveries is supernova 2009ij in the galaxy UGC10923 which is within a few degrees of Polaris so relatively easy to find. Follow-up images of discoveries are always wanted so, on 28 August, I decided to try to image it with the new telescope. The image below is a composite of 8x1 minute exposures; it shows that the supernova has faded significantly since its discovery and is now just below 18th magnitude. The discovery image, for comparison, can be found at: https://www.coddenhamobservatories.org/discoveries.htm.

PFR.jpg The 30 cm prime focus reflector.

M51.jpg M51

M108.jpg M108

20090828_SN2009ij_MJH.jpg SN2009ij

Mike Harlow