Classic LX200 imaging results:

Intro: Using large CCD detectors, the classic LX200 is no longer suitable for imaging unless an adapted corrector is used. For the native F/10 classic LX200 they are on the market but expensive. I doubt they will work well for the native F/6,3 classic LX200. So my old 8 inch classic LX200 F/6,3 will in future used for visual observations only or as an image platform. Here some of my thoughts and experiments to trying make it working before I bought other telescopes:

Optical test bench results: In October 2013, a test of the telescope a test bench of  H. Dekker showed pretty good good airy disk star patterns without the focal reducer. So for visual purposes it is good telescope except maybe for reduced contrast due to the obstruction. With the focal reducer mounted, the results where not good, so it looks like this part needs to go. Remains the strong focal curvature which is a problem in combination with the large modern CCD chip.

LX200 test bench results:

Field curvature and coma: One of the main problems of the classic LX200 is the field curvature. Using the large CCD it also suffers from coma in the edges of the field. With the Celestron F6,3 focal reducer images look better but shows strange optical errors in the corners like the polar axis is not good This is caused by the poor optical quality of focal Celestron reducer made in 1999.  Experiments with the CCDT67 reducer are also disappointing.

Since these optical test bench  results where good, it motivated me to try to find a fix for the curvature. I couldn't find any details regarding the LX200 curvature so I did an analyses myself, see: Analyses of the optical parameters classic LX200

Flattener experiments: Experiments using a low cost Skywatcher/Orion refractor field flattener for the LX200 where not very successful. I'm afraid the standard field flatteners will not cope with it fully.  So it is time to move on and start using the APO65Q en the GSO RC for for imaging.

Vignetting: The LX200 native F/6,3 large secundairy mirror combined with the large CCD chip could easily result is vignetting. Unnoticed most of my LX200 image have been made with this problem. For my CCD chip the T2 pipe should be equal or less then 70 mm long. Also the 2" pipe shouldn't be too long. With my T2 off axis guider about 60 mm maximum. Using only a Crayford focuser connected directly to the camera , the length should be equal or less then 130mm otherwise vignetting will take place. Since the math can be a little tricky, I made a spreadsheet calculator  for this.

NGC2024 and IC434

8 inch F6,3 LX200 telescope with focal reducer at F4, QHY8 oneshot RGB CCD camera. exposure 16x500sec on 2011-10-2

han.k, 2014-10-11