Zeiss AS80/1200
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 exhibits, due to combination of KzF2+BK7 glasses, reduced color abberation with respect to the clasical achromat. Having color index of 2.0, it was classified by Zeiss as semi-apochromat.
Currently I own two pieces of this nice lens. The first one is coming from the Eastern Germany time and it is probably from 80ties or early 90ties. It has good optics, star test shows only small undercorrection. The second one is much older, it dates probably somewhere around 1930-1935. The lens is put into the brass cell and glass has no coatings. It is in excellent condition, the glass seems untouched and like new. Star test reveals only slight astigmatismus. Performance of the lens seems not to be affected by it. The lens is sharp and provides a lots of detail on Jupiter.
I bought the Eastern Germany lens in 2011. It came with home built aluminium tube, nice Zeiss revolver head with zenithal mirror and two Carl Zeiss Jena orthoscopic eyepieces: O-12.5 and O-10. I added Zeiss helical focuser to it, new baffles, and finder.
The main advantage of the scope is very fast thermalization. In direct confrontation with apochromat SV80S, AS80 was showing much better image of Moon. SV80S apochromat was getting closer and closer to the image in Zeiss but it was not there even after one hour. And this was just about 10C difference between inside and outside. Similarly, one can notice quicker thermalization of AS80 than ED100. In winter, AS80 is the telescope I take out for short sessions.
