Posts Made By: dan kowall

The Rosette is especially nice, Eric.

dan

Paul Maxson said:
.......I'm not sure why M52 is showing little colour, but it definitely has a 3 colour histogram.
M52:
http://web.gccaz.edu/~pmaxson/DSO/M52.jpg

Hi Paul,
Open your M52 in Photoshop or any program that can give you pixel values.
The usual cause for all white stars is that the stars are saturated in all three channels.
The stars in the black band at the top all show saturation in all three channels, hence bright, white stars.
The rest of the stars show mostly equal values in the three channels, which equals white, but they are not all saturated.
I suspect that you lowered the white point on these stars at some point in your processing which is why they are not saturated now. They probably were at acquisition, though.
Most of your stars have a donut appearance. This comes from too aggressive sharpening. I know it's tempting when starting out to call on a sharpening routine to pretty things up, but I would advise you to not do any sharpening until you've mastered the basics. Sharpening works best on really good data and when applied selectively and lightly.
The 'cure' for saturated stars is to take shorter subexposures. When doing a test exposure measure a bright star. A non-saturated red star will have values such as R=230, G=140, B=140, for instance.

I hope this helps,

dan kowall

What an artistic pairing of these two, Jim!
That's superbly framed.
My regards,

dan

Shorten your exposure time until the Trapezium doesn't show saturated nebulosity.

dan

Jason Boyce said:
....I took flats for all my filters but ended up not using them as they seemed to do more harm than good.While they did get rid of some dust and dew spots they made the background very uneven in illumination from one side of the frame to the other.
Maybe this is from the light pollution gradient in the subs?.....

Hi Jason,
The 'bad' effects of light pollution, and not using flats can indeed be hidden by raising the black point. This comes at a high price, though. Good data gets tossed out, too.
I think you were right in thinking that light pollution gradients were responsible for what you were seeing after calibration. Why not go back to that point and remove your gradients to see what you get then?
Flats are an essential part of processing; I don't know of any accomplished imager that doesn't use them. Taking flats is sometimes called an art form since it takes some skill to get good flats. The test of a good flat is "does it work?". In your case, since it did remove the dust spots, I would say that your flat was probably good.
Russ Croman has a fine gradient removal tool:
http://www.rc-astro.com/resources/GradientXTerminator/index.html
as does Ron Wodaski:
http://www.newastro.com/newastro/downloads/rem_grad/default.htm
Removing gradients manually in Photoshop is a handy skill to learn, too.

dan

I'm glad to see that you'll be up and running soon, Ivan.
You have a nice, clean design.
I hope this one is well anchored to the ground.
My regards,

dan

The color is just as it should be, David.
Good job.

dan

Thanks for giving me my first view of that nebula, Louie.
Even the large image looks good.

dan

Very nice, Dietmar.
If one goes for really long exposure on this galaxy, a red shock wave produced by one of the bipolar jets in this galaxy becomes visible. It's just coming visible in your image. Congratulations, that is not often seen.
My regards,

dan

Hi Sam,
You've saturated Alnitak and some other bright areas (maybe white clipped?), but your color and detail are excellent.
You're undersampled at almost 4 arcsec/pixel but you've really made it work here. It sure makes for a fine field of view.
My regards,

dan