[APML] First images posted: vignetting correction, circular cropping

[Ray Butler <ray.butler@nuigalway.ie>]

Hi folks.

Since I joined the list about a year ago, some of you may have noticed 
that I talk the talk, but wondered if I walk the walk? (;-))

I guess that being a research astronomer has instilled a very cautious 
attitude: you never publish your results until you are entirely happy 
with them, and are confident that you've covered all the angles and 
gotchas. Since my hobby astrophoto "data" is of limited quantity and 
imperfect quality, I have concentrated on squeezing the most out of them 
by developing my own digital processing methods. The problem with this 
is that it can go on forever - one is never entirely satisfied with the 
result. Little gotchas always remain, especially the higher order 
residuals when one tries to do photographic vignetting correction..

But now I've decided to just say "that'll do, pig" to myself, and start 
publishing some of my images online. I'd like to thank Dave Kodama for 
prompting me to do this - if he hadn't asked me recently to show an 
example of my circular cropping technique, I might not have taken that 
step yet!

The first example is here:
http://tinyurl.com/9re5f

It is a nice illustration of a few things you don't often see:
- Medium format (6x4.5cm) through a bog-standard 2" focuser
- Use of a fast achromat (what, no APO?!) with medium format
- Use of a fast refractor out to a wide field (wider than on 35mm) 
without a field flattener/reducer
- Manual guiding (in this day and age!)
- Use of a heavy-duty mount which is actually very affordable (EQ6)
- Automated multi-scan scaling & coaddition with scanner saturation 
removed by masking
- Automated rebate intensity subtraction and rebate cropping
- Automated channel registration (lateral colour correction)
- Automated vignetting/gradient correction (could be a bit better)
- Automated circular cropping (- Dave, this is what you wanted to see)
- Automated levels set by image's own statistics, for final RGB 
recombination

I guess this is the point where I am supposed to say: "Comments & 
criticisms welcome" !

Ray "who is still a bit apprehensive about releasing flawed results" Butler

-- 
Dr. Ray Butler
Lecturer, Physics Department & Computational Astrophysics Laboratory,
National University of Ireland - Galway, 
University Road, Galway, Ireland. 
Web: www.nuigalway.ie/physics/ 	Email: ray.butler-AT-nuigalway.ie 
Tel: +353-91-493788 		FAX: +353-91-494584

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