British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

Home Forums Telescopes
Terms of use

SCT Reflections or Ghost images

3 posts / 0 new
Last post
Offline
Last seen: 6 years 5 months ago
Joined: 10/01/2013 - 12:11
SCT Reflections or Ghost images

Posted by Paul A Brierley at 06:43 on 2012 Mar 29

A very good friend of mine, uses a H18 CCD camera with this Celestron 8" SCT.He has a curious problem, and I am hoping some of you might have an answer.If you look at the attached image you will see what I mean.My theory is. We are seeing a ghost image, of the SCT corrector, and secondary.But what is the cause and is there a fix.The SCT has been flocked and is carefully collimated.

Offline
Last seen: 6 years 5 months ago
Joined: 10/01/2013 - 12:11
Re:SCT Reflections or Ghost images

Posted by Roy Hughes at 18:15 on 2012 Mar 31

It may not be useful, but here's my thoughts.1. It looks like a very out of focus star as seen visually in my Celestron C8.2. It's off centre.Have you got an artificial star just outside the field of view, and rather closer than infinity?Maybe a chrome screw on the tube. An over long screw securing the corrector plate might do it, on my old C8 they poke though the tube and just stick out on the inside.Roy

Offline
Last seen: 6 years 5 months ago
Joined: 10/01/2013 - 12:11
Re:SCT Reflections or Ghost images

Posted by Paul A Brierley at 06:48 on 2012 Jul 02

Just a quick update.The problem was a very loose secondary that was only hanging on by a thread. The secondary as been re- attached using silicon glue, and their isn't a problem.