How many Images can i stack

[johnb]

Hi

Ive been readin the stiky which talks about basic camera an tripod, im curious - is there an ideal numbe rof immages to capture which you then process, the article suggests 10 exposures (ISO 800, 30 seconds) and 5 dark frames - is there any advantage to say 20 exposures ?, is there a cut off were its just not worth doing any more ?

Regards

John B

[ollypenrice]

Hooooo yes, do more and more and more and more!!! I think there is a point at which your signal to noise gain vanishes to nothing but I have never reached that point. If I can get five hours in five minute subs of Luminosity then I do. The best images have one thing in common; very long exposure totals. The advantage is less noise and even when your stack reaches a point when, at first sight, adding the same again does not make much difference, wait till you start to process. Then you WILL see a difference. You can stretch and sharpen a really deep stack where a shallow one will just turn to grainy noise.

One thing, though; it can be as well to make sub stacks if you have a very long run. Say you have 4 hours. Make the first two into Stack A and the next two into Stack B and average combine them after careful alignment/co-registering. If you don't, any defects in your polar alignment will produce trailing effects.

Get yerself a tinny or two and settle down for the long wait!

Olly

[jgs001]

John, the more the better. The problem with using a tatic tripod, after a number of subs, I must admit to not having worked out the number, but it's more than 10 and quite a bit less than 30, field rotation becomes a problem and 2 corners start to smear. The more subs the worse the smearing gets and more of the image is lost. I suggested 10 as a starting point as I've not had smearing with that number of subs. I'll see if I can find an example when I get the chance.

[brianb]

The problem with using a tatic tripod, after a number of subs, I must admit to not having worked out the number, but it's more than 10 and quite a bit less than 30, field rotation becomes a problem

Not with DSS, which will rotate the field to get a proper match.

If your lens has marked distortion, field rotation correction will not work properly. That's a different issue.

[minimalist]

I would also suggest using more than 5 darks. Darks don't reduce random noise, which is the main noise in dslr's. Darks reduce hot and cold pixels and amp glow. If you own a camera like the 400D or newer, you don't have any amp glow to worry about.

Actually, I'll be the maverick and suggest not using darks at all. In DSS, you can use Kappa-Sigma as the stacking method, and using at least 10 light frames or more will remove hot and cold pixels without using darks. Tbh, the only place I've found darks useful in the newer dslr's is pattern noise (like banding noise). But that only happened to me occasionally, and my 1000D and 40D have never experienced it as far as I can tell.

I know, most folks use darks, so take my advice as a personal opinion.

Daniel

[Beyond_Vision]

As BrianB says DSS will cope with field rotation but the size of the useable area will decrease. As each frame is overlapped the amount that overlaps and is 'added' together will get smaller.

Regards

Kevin

[jgs001]

As promised, here's the example...

Note the upper right and lower left corners. That effect does not appear on the source subs, only post stacking. This was some 30 or 40 subs, I can't remember now as it was about this time last year. This isn't going against what BrianB said, but agrees with Kevin... There's a limit to what DSS can do with large numbers of static images. I guess my description of it wasn't accurate enough.

I have found with my 450d, that I can get away without using darks (in fact, my images actually seem better without them, with more details and faint fuzzies).