Double Quasar, QSO0957+561
A gravitational lens is said to occur when light from a distant object is bent by the mass of an intervening object so as to form multiple images of the former. In 1979, the double quasar, QSO0957+561, was the first example found of such lensing involving quasars. It is thought to consist of a very distant quasar which appears as two separate images due to gravitational lensing associated with an intervening galaxy. (The intervening galaxy is designated YGKOW G1.)
I imaged the object on 17-18 April 2018, using a Celestron EdgeHD 200 mm Schmidt-Cassegrain telescope with SBIG 8300 camera. One image of the quasar is clearly visible but, in my amateur equipment, the other is coincident with the intervening galaxy. A bigger scope and clearer skies are necessary to see both separately! In the inset image, the quasars appear at approximately magnitude 17 and the two stars at approximately magnitude 19.