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Stacking images vs. Longer exposure time

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18 years 4 months ago #24554 by Eirikg
Im wondering what is prefered, pros and cons for theese methodes? I know longer exposure will give more noise, what are the negative sides of stacking images?

And do you collect equal amount of light with 8 sec eposure and 4sec x 2 exposures?

I have been testing some with piggybacking my cheap digital camera. But seems i have to stack ALOT of images compared to as haveing one long exposure?

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18 years 4 months ago #24555 by dmcdona
Replied by dmcdona on topic Re: Stacking images vs. Longer exposure time
As well as collecting more noise, a single exposure collects more signal!

The preferred method is to take as long a single exposure as you can. Then repeat and stack them.

In general, one 8 sec exposure will be better than 4 x 2 sec exposures. Of course, these exposure lengths are more for deep sky than planetary imaging.

One final note, the longer the exposure the better but at some point, your exposure length will reach a limit as sky-glow starts to interfere. So there is an optimal limit, depending on where the scope is pointing...

HTH

Dave

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18 years 4 months ago #24557 by Eirikg
ok i was thinking for Deep sky

So best is expose as long as equpiment, guiding, ect can handle then stack

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18 years 4 months ago #24560 by dmcdona
Replied by dmcdona on topic Re: Stacking images vs. Longer exposure time
You got it...

Also, beware. Your mount will track at differing rates depending on where its pointed in the sky. You may get 1minutes exposures with no trainling in one part of the sky, but less than 30 seconds in another part of the sky...

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18 years 4 months ago #24562 by dave_lillis
Replied by dave_lillis on topic Re: Stacking images vs. Longer exposure time
Eirik,
Its an interesting question which is worth spending abit of time thinking about.
If you bring the comparison to an extreme, is 60 1minute images stacked the same or better then a 1 hour exposure ??, the answer is an emphatic NO.

The longer the exposure, the fainter the detail in the image, I've found that stacking deep sky images really brings out and sharpens the detail, but doesnt significantly increase the limiting magnitude. I have Orion nebula images on this site that show this.

In order to get very faint detail you need a longer exposure, there is just no getting around it.

Dave L. on facebook , See my images in flickr
Chairman. Shannonside Astronomy Club (Limerick)

Carrying around my 20" obsession is going to kill me,
but what a way to go. :)
+ 12"LX200, MK67, Meade2045, 4"refractor

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18 years 4 months ago #24564 by Eirikg
that is what my tests showed also

Deep sky isnt my aim with what i got now, but im thinking of buying LPI.

So then the question is, i see wind is a big factor at high magnification, would it be better to then take loads of short exposures?

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