Hi to all! My newly made OTA with Sheldon Faworski's ED127 triplet objective has a problem. I centered the lens last night (push pull lens cell screws and radial lens element collimation screws) to elliminate axial decenter coma and lateral colors and all was fine. The scope was on my homemade eq mount and I used 5 star artificial sky lamp. Telescope worked excellent at highest magnification I can get, 310x (barlow 2x and 6mm Gold line ep. The collimation was done with my camera and a laptop in live view mode in APT software for me to see what I am doing. But when I lifted the scope to near zenith to do a real star test, all I saw is a significant coma and lateral colors. Procyon was a rainbow! It was very high at the sky at that time so that was not an atmospheric dispersion! I then returned the scope position back to my artificial star and the image was fine again as it was when I collimated the lens! The collimating screws are tight enough for prevent any movement of the lenses! So I think something is wrong with the tube. It probably sags a lot! The tube is PVC-C used for swimming pool instalations. It is 140mm O.D and 5mm thick wall. Near the focuser I put a finder and a guider next to each other and mounted in their aluminum rings. I have no rings for this telescope so I screwed the Vixen dovetail directly on the tube. Now tell me what to do... Should I afterall need to switch to aluminum tube which was impossible to find here in these dimensions, or is it enough to put the rings on my scope on the longest dovetail I can find so the rings would be at the ends of the tube for stability and to prevent sagging?
Edited by Stipe Vladova, 11 October 2019 - 05:51 AM.