Long vs. Short Subs

Hello,

I am looking for some feedback; assuming that light pollution and guide error is not a factor, am I going to have better results shooting 20 minutes for each sub, as opposed to 2 or 5 minutes?

Are 5 stacked 20 minute subs better than 20 stacked 5 minute subs?

Now, since I typically work from a light polluted location, should I just try for the longest subs I can get without excessive noise?

Thanks for your help, and your opinions!

Keith

Yes.

I just answered this question in response to another post, but I'm not above repeating myself.
You want your subs to be as long as possible without saturating your object. In practical circumstances, though, sky glow from light pollution is going to be a limiting factor.
The hard work in figuring out exposure times has already been done by others:
http://www.ccdware.com/resources/subexposure.cfm
The instructions will have you take a 3 minute test exposure with a dark applied. Once you've plugged in the numbers for your system, an optimum exposure is calculated.

dan kowall
photonhunter.com

Hi Keith,

The real answer is "depends".......how bright is your target, what type camera are you using, and what are your other conditions (like skyglow). There isn't just one answer to your questions - but there have been some papers written (and arguements over the conclusions) on the subject.

If your stars aren't saturated - longer subs are going to be better......but past a certain point, not much better than just using more but shorter subexposures (are your confused yet?) Here is a write-up on the subject if you love the math......or just use John Smith's (CCDWare) calculator (as other's have suggested). The real object is to get the best data for your conditions and equipment......and to do that you just have to try different things and see what works best.