Quote:
Originally Posted by Jon
Sorry, sorry - imprecise use by me of the word "you". What I meant to ask was "why can't one/somebody just use filters with an achromat, and adjust focus?"
I thought one of you guys might have the answer. If one could, why are all the big guys imaging with monochrome cameras through apo refractors?
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The question is a bit beyond my experience, I'm an RGB newbie but I'll have a go at answering it. From what I've read, narrow band imaging is fine through an achromatic refractor. RGB filters for imaging however are wider bandwidth than the narrow band Ha / S2 / OIII etc. I think (someone correct me if I'm wrong) that with RGB some CA still gets through with the wider bandwidth. It certainly does with my primitive GSO green and blue filters. I'll upload a pic to demonstrate.
This is the Crux star Mimosa taken with GSO red, green and blue filters. As you can see there's still blue and magenta CA on the green and blue filters even though I've focused on each filter separately. Does this still happen with better filters like Baader etc? I'm not sure and would like to know myself. Need to get one of the pro shooters to answer this for us.