Ideal exposure

I've looked at the manuals and the books, but I cannot find a good answer--or it has gotten lost in the tons of stuff I have seen.

What exposure should I shoot for with my CCD camera?

My experience with DSLR says shoot for as long as mount, skyglow, and saturation allow. That is, keep the shutter open until the stars record at the maximum sensor reading, unless that means you get too much skyglow or the mount inaccuracies are showing up.

Just what does that mean with a CCD. With CCDSoft 5, I saw that my exposures were reading 54000 or so max--which is close to saturation, but when I actually pulled them up to start processing, they were very dim.--only about 4000. Am I getting fooled by the viewing software auto-correcting or something in the display? Does the Max value in CCD soft show the saturation of the of the brightest pixels, or something else?

In short--how do I decide how long to keep the shutter open?

Alex

Your basic experience with DSLR is still valid.

You want to expose long enough that the noise in the sky
background is much larger (several times larger) than the
"readnoise" in your CCD. You can measure these parameters
directly by taking some very short (for readnoise) and longer
exposures (for sky noise). Most CCD programs will
let you measure the noise (or RMS or standard deviation)
in some blank area of the image.

The exposure should also be short enough to avoid saturating
any part of the image that you care about. And short
enough to avoid any visible tracking or guiding errors.
Shorter exposures have the obvious advantage that you can
throw-out less "time" if theres a guiding glitch, cloud,
airplane, etc.