Zeiss AS110/1650

Legendary lens from Carl Zeiss Jena. Lens of type AS was in production since 1923 (in the beginning, they were marked as old line type A, although of different nature and construction) until the closing of Zeiss astronomical division in 1995. The lens was designed by Dr. August Sonnefeld and has, due to combination of KzF2+BK7 glasses, reduced color abberation with respect to the clasical achromat. Its color index is 2.7.

This historical piece is coming from year 1924 and is probably one of the first 110mm AS lenses sold under this name. After tuning the spacers by optician, the lens exhibits very good optics. Star test shows only minor undercorrection. I was able to resolve with this lens some unequal doubles even slightly below Dawes limit, for example lambda Cygni (4.7+6.3, 0.9''). It looks like that the glass is put under strong stress in cold weather.

Unfortunately, the historical value of the lens is lessened because the previous owner got the glass coated. It looks like it did not affected good performance of the lens.

The impressive brass focuser is original. It works very well with minimal image shift and one can easily use it in magnifications well above 200x. Also a set of old Zeiss ortoscopic eyepieces with large 40mm Kellner and straight revolver head came with the telescope. Unfortunately, the eyepiece tubes are hair wider than in current 0.965'' eyepieces. Luckily, I can use at least od 5mm ortho which I could press to my 0.965''->1.25'' reduction. I also found old Zeiss terrestrial binoview. Unfortunately, I can't focus with current 2'' reduction and new must be built.


Thanks to new aluminium OTA, the telescope is surprisingly light and my equatorial mount Losmandy G8 can handle it just fine. Original plan was to buy better alt-az mount and keep the telescope at home for watching Moon and planets. But it sits so nicely in the observatory that I'm going to keep there for a while. Observing with such long old telescope is simply very unique experience.


by Alexander Kupco