[ATMoB-discuss] First photo from C14/ST7

[John Boudreau]

Hi Bruce, I guess it's my turn to chime in here <g>.

First of all, I think you've done very well for a newcomer to this crazy thing called CCD imaging ;o)

Yes, darks are intended to null out pixel variations, but even darks themselves taken moments apart vary a bit (that's why we median combine several of them)--- there's never a perfect null for each and every pixel, and there's usually a few that seem to remain untouched ;o(

Sorry if I'm about to rehash something you already know...

I just reviewed the basic CCDSoft image reduction routine. Saturday night we had started with 3 minute sub exposures and then decided to go for 5 minutes, so you have a mixed bag of sub exposure lengths to work with. To properly reduce these, you needed to take darks preferably 5 minutes or longer. 

If all the M57 subs were 5 minutes long, then you could just use 5 minute darks _without_ taking bias frames. But since we took some 3 minute subs that you want to use, bias frames are then used to allow the software to properly scale the 5 minute darks to the 3 minute subs. The darks should be median combined, and dark exposure correction set to 'automatic'. Bias frames should be median combined too. In this case there are no flats, but if there were they should also be median combined. 

Each M57 sub should be reduced in it's folder (in this case dark subtracted), then you can run the alignment procedure. The resulting reduced and aligned sub images folder can either be combined by adding, or by median combine. 

The resulting image can then be processed in CCDSoft and Photoshop, or whatever you have. As I don't use CCDSoft myself, I'm not familiar with hot pixel repair and the like with it. Hot pixels are easy to discern from small star images, and so are easy to clean up with the Photoshop clone tool.

For future imaging, it's best to use dithered guiding for the individual sub exposures. Here's a link for a very good freeware dithering plug-in for CCDSoft: http://pk.darkhorizons.org/AutoDither11.htm
I've used it, and it's actually nicer than the dithering setup in MaxIm.

There is a form of combining called 'Sigma' that gives an overall cleaner image than the forms in CCDSoft. Here's a link to Ray Gralak's Sigma freeware: http://www.gralak.com/Sigma/
MaxIm has a version of Ray's Sigma program built-in.

If you plan on looking into another image processing software, let me know. I'll soon be trying out a fairly new one that several imagers I know have recently switched to--- CCDStack by Stan Moore:
http://www.ccdware.com/products/ccdstack/
It's $200, but there is a 30 day trial version.


---John Boudreau