“The design is an airspaced douplet short-flint semiapo. The colorcorrection of these optics - which are real semiapo - is very similar to modern douplet ED-Apos. The images on both sides are extremly uniform and super smooth. The only visible difference between inside and outside of focuse is due to a minor chromatical aberation which smears a bit. By using a green filter, one would not be able to tell which image is on which side of focus, since they look 100% equal. Zygo testings (at 632 nm, which is considered less usefull) has showed us in past that these optics have strehlratios over 99%. This type of lens is what experts call to be manufactured to practicle limits” Markus Ludes (APM-Telescopes) |
