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C-5 problem please help
I hope someone can help me. I have a white tube C-5 that used to show
perfect star test patterns on both sides of focus. I have since installed Bob's Knobs, for collimation adjustments. The collimation seems to be very good, however. when I defocus a star I can see what looks like spider vein diffraction patterns, running N/S/E/W. When I rotate the eyepiece or diagonal they do not move. The cross pattern does not show up in focused images [however the seeing has been so bad that I can not use high enough power to see the airy disk. Has anyone else seen this in there scope? Thanks in advance Steve |
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C-5 problem please help
"stevew" wrote in message
... I hope someone can help me. I have a white tube C-5 that used to show perfect star test patterns on both sides of focus. I have since installed Bob's Knobs, for collimation adjustments. The collimation seems to be very good, however. when I defocus a star I can see what looks like spider vein diffraction patterns, running N/S/E/W. When I rotate the eyepiece or diagonal they do not move. The cross pattern does not show up in focused images [however the seeing has been so bad that I can not use high enough power to see the airy disk. Has anyone else seen this in there scope? Thanks in advance Steve I've seen similar things due to uneven temperature and bad thermal equalization. I haven't seen them at 90-degree angles, though. Is there anything streaky on the corrector plate? Also, see if the secondary holder is off center. This is an odd problem I have observed with my old C5 and with a NexStar 5. If it's off center, just push it sideways until it's centered (you may have to push moderately hard) and then recollimate. |
#3
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C-5 problem please help
Hi Steve,
It's possible that the secondary mirror can be slightly deformed by overtightened collimation screws. However, it is usually visible as a misshapen airy disc, rather than diffraction spikes. I overtightened my 2045's screws, and it caused the disc to appear slightly triangular. The problem disappeared when I adjusted the screws until they were just snug. Best wishes, Jason Glass "Brevity is the soul of wit..." -Polonius in "Hamlet," Act 2, Scene 2, by William Shakespeare |
#4
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C-5 problem please help
It's possible that the secondary mirror can be slightly deformed by overtightened collimation screws. However, it is usually visible as a misshapen airy disc, rather than diffraction spikes. Hi Jason: Exactly. In my experience, over-tightened secondary screws result in a classic pinched optics triangular diffraction patterns, just as you observed. My guess as to the problem with this C5? Seeing or cooldown. Peace, Rod Mollise Author of _Choosing and Using a Schmidt Cassegrain Telescope_ Like SCTs and MCTs? Check-out sct-user, the mailing list for CAT fanciers! Goto http://members.aol.com/RMOLLISE/index.html |
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