Quote:
Originally Posted by Prickly
Hi Peter,
Thought I had the focus ok but I'll see what happens next time. The main star images seem reasonable. The double ring around the brighter stars is whats got me. Has anyone experienced that with poor focus?
A little bit of CA on very bright objects I can accept (yes it is a refractor) - there will definitely be a small amount but in DSLR images it hasnt been too noticeable.
I'll also be seeing if the flip mirror unit could be contributing in some way by removing it from the equation and as mentioned will be very careful with focus.
The double ring halo has me quite perplexed.
Cheers
David
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The 'halo' is similar to what I experienced with my own refractor made from Surplus Shed optics - an achromat only - so there was still some chromatic abberation on prime focus images through my DSLR - no matter how well they were focused. But the halo was more pronounced the more out of focus I was. I have partially eliminated this by using as Baader Fringe Killer filter. This blocks most (but not all) of the offending ends of the soectrum that were causing those rings.
You may like to ask around and see if you can borrow one for a bit of a test run and see what that does.
Peter