A 155,mm triplet Oilspaced super ED Apo.Don't look at the little amount of astigmatism. This comes and goes, under the real sky it is not visible. On the benchtest it is from time to time visible. The Ronchiimages show a bit overcorrection, also you can see a tiny central zone,which is visible in theeyepiece too,its not a dirt spot,its a real zone.
Overal correction is good, startest in green color is excellent
Markus Ludes (APM-Telescopes)
Collimator : 9" F/9 Triplet Super ED TMB Apo / ronchi : 254 lines/inch or 100 lines/cm.