Telescope Reviews: Yet another M13

slenarz,

Thanks alot!

Unfortunately I did use PS to use layer capability.

Basically I took two stacks
30x180 sec, ISO 800
10x120 sec, ISO 800

This is the first time I've tried this, so there may be more optimal ratios etc.

Align ALL frames in IP (120s and 180s frames so they are all registered the same)
Stack just the 30x180s with avg combine
Digital Development - Adjusted the break point until I was happy with star exposure (in this case the number of stars toward the outer edges of the cluster). At this stage some of them are still pretty weak, and for the brighter ones color is disappearing - don't sweat the color for this stack
Adjusted the background weight so there was no background clipping (check with the histogram in IP). At this stage I had a gradient on the right, but I was going to kill it in PS
save off this stack
Now stack the 120s frames in a separate file
Digital development again on this stack, but be much more gentle with the breakpoint, the goal is to get enough exposure to ID the larger stars and save some color, don't worry about the faint stuff
for this stack, I left the background clipped - BLACK. I'm going to use it for a color layer only and I don't want the background to have a color in this case
Up saturation - overdo it a little bit because I'll use a Gaussian blur later
Now import both stacks into PS, put the 120s stack on top of the 180s stack, and choose overlay=color. The point is for the 2nd stack the only purpose is to apply the color. I got this idea from the LRGB approach. I concentrated on exposure with the 180s stack and color on the 120s stack.
Applied a ~1px Gaussian blur to the 120s color layer to remove some noise

That's the gist of it. I also did some more curves adjustments on top of the 180s stack (below the color layer) to bring out some of the fainter stars, and used some masking to avoid blowing out the core.

On top of it all is a levels layer to set the background to as close to 30,30,30 I could get w/o going over that.

The advantage to this method is that you don't lose color in stars by over exposing (which will happen naturally with any long exposures), and you decrease color in the background by slightly clipping the color layer. Any color gradients (which I have alot of) in the background are at least reduced.

Of course this would not work for nebula, I understand that, but it seems to work nicely for the cluster. I'm reworking my M5 with this method too and it is definitely getting better.

I hope this helps, or at least helps with some ideas!

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Cheers,
Jon

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Orion Atlas 8" (203mm f/4.9 on Atlas EQ-G)
Tasco 60mm (~35 years old and still kicking!)
Nikon D300, 80, 70 & many lenses
http://www.pbase.com/jmasin/astro