Stacking Images Is there sucha thing as overkill

I have saw a lot of images taken of objects in space ranging from 1 exposure to 100 or more exposures stacked on top of each other.

Is there a point where it becomes wasted time and unnecessary wear and tear on the shutter.

Let's assume you are shooting at 1600 ISO in dark skies. I like to stack between 20 and 30 exposures at this ISO. Any more than that does not seem to affect the image any more.

So what does everyone else think of this.

The law of diminishing returns applies. Most people find that pending on their camera, conditions, and etc the balance is around 40-50 images. I have done as much as 170 when testing this. Here's the kicker, MORE SHOTS can REDUCE the quality of your final product if you introduce not so good shots in the stack. The best bet is to shoot MORE then you need, and pick the best subset you can. In that stack of 170, I actaully got better results when I threw out 50 or so images.

WebCam users shoot in to the 1000's of shots to stack, but that is a different game, and the rule still applies, just at a different scale.

I have to agree that poor images are counter productive. When I get the 50D, which was supposed to be here today, I will check to see where the results start to be ineffective with more exposures. The Sony is really hard to figure out because of its long exposure, high noise, purple death, detail destroying effect. Sorry, but it's aweful at long exposure, high ISO imaging, even with the in camera noise reduction cranked.

It depends on what the parameters of the shot are. It's about 40 images at a single exposure length and ISO that you'd want to stack, and make it good ones if you can help it. If you shoot 40 images at 30 seconds and ISO 1600, then do 40 at 60 seconds and ISO 800 you'll want to stack all 80 because you'll get an even better result since the 30 sec and 60 sec will have different amounts of signal and noise.

Don't forget, the more you stack the more you reduce noise. If you're in super dark skies you might only have time to do 10 5 minute shots, but they'll be incredibly detailed if you have good tracking because so much is gathered in a sub that long. Do the longest shot your skies and tracking allow, but try to take as many as possible because if you had a long night and did 40 5 minute subs you'd have a ridiculously good shot most likely.

Sounds very logical. I am going to start trying my luck at long exposures when the 50D gets here. It will be much easier when I can control the camera from the computer via usb cable. I have set up ascom on my computer and will start using it along with phd guiding to track. That is the main reason I purchased the Stellarvue 80ED; so I could guide with one scope and image with the other.

Thanks for the input.

Have to go see if my 50D is here.