Hi
I recently bought a GSO 8in Ritchey Chretien scope and although the weather in Sydney has not permitted any serious imaging with it I have run it through its paces for focusing and images tests. Please see the attached 20 second image of Rigel taken with a modified Canon 400D camera with lpf on the 8in RC at f8. I know Rigel is a very bright star but with only a 20 second image I was surprised to see an apparent "ghost" reflection of the RCs secondary mirror behind the image of Rigel. Longer test images of this star worsened this effect. Is this test too tough?
I see that there has been a previous thread regarding flaring on images by nearby OFF screen bright stars but I was told that this problem with the inner scope tube had been rectified. Any comments?
Cheers Peter
Peter,
I can't view your attached image properly for some reason, but I would say this is a reflection from the CCD back to the LPF and then back to the CCD.
If it worries you, then don't use the LPF. Most of the time it will be ok becuase the stars in your image are not so bright.
James
This issue is different from the described problem that existed in these scopes. This reflection is common in a lot of telescope designs on brighter stars. If you want to see what the previous issue is it can be seen below
Thanks James and Paul for your comments. James - I will look into your suggestion. My lpf is of the clip in variety and it could be the culprit.
Paul - although it looks not to be my problem I have saved your beautifully prepared instructions about tube flocking for possible future use. I really need to get on with some proper imaging. I hope to image the Flame nebula which is close to the bright star Alnitak. This should be a good test of my possible bright star problem. Cheers Peter
Peter,
One other point to note - if the surfaces are flat, it's not too hard to calculate the distance of the offending surface causing the reflection.
There's an example here.
James
Yep. Except for yesterday when the weather went from overcast to cloudy to amazing storm and then - wait for it - clear all night. Not sure if one day of Melbourne weather can ever be encapsulated in a single icon. Perhaps another animated gif is required, but instead of day, it needs hour.
