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Archive 2017 · Multiple short exposures stacked = 1 long exposure without noise?

  
 
nandadevieast
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p.1 #1 · p.1 #1 · Multiple short exposures stacked = 1 long exposure without noise?


Hi
As the title says, can we AVOID USING NDs or LONG EXPOSURE NOISE by stacking multiple shorter exposures? Like instead of taking a 2 minute exposure, what about many 1-2 second ones?
Does this make sense in landscape photography? I know people do this in astro photography...



Mar 03, 2017 at 12:48 PM
dhphoto
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p.1 #2 · p.1 #2 · Multiple short exposures stacked = 1 long exposure without noise?


A shorter exposure will be grossly underexposed, unless you opened the aperture or boosted the ISO, or both, not sure how that would work out


Mar 03, 2017 at 01:04 PM
nandadevieast
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p.1 #3 · p.1 #3 · Multiple short exposures stacked = 1 long exposure without noise?


Yes, ok, thanks

dhphoto wrote:
A shorter exposure will be grossly underexposed, unless you opened the aperture or boosted the ISO, or both, not sure how that would work out




Mar 03, 2017 at 01:29 PM
AvianScott
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p.1 #4 · p.1 #4 · Multiple short exposures stacked = 1 long exposure without noise?


Yes, it can be done for landscape photography. There are many more tutorials out there besides these.




Mar 03, 2017 at 01:48 PM
alundeb
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p.1 #5 · p.1 #5 · Multiple short exposures stacked = 1 long exposure without noise?


We have three noise sources in long exposures, photon shot noise, read noise and thermal noise.

Photon shot noise is the easiest here. It will only depend on the total accumulated exposure, and not depend on how you do it, one or multiple exposures. Since we use low ISO it will be very low anyway.

Read noise will add up for every new exposure. Read noise will show up in the deepest shadows. If you don't require very large dynamic range, this may not be significant.

Thermal noise is the noise that get annoying with long exposures. This will add up with the total exposure time, and thus not be any different from taking one exposure.

This is assuming that you use the ND filter when taking multiple exposures.

If you remove the ND filter, and the take multiple exposures that all capture more light, there will be a large benefit in stacking multiple exposures. The noise will be averaged instead of added, thus ending up lower.

The reason we don't always do it ,in addition to the extra work in post processing, is because there will be a delay between the exposure that may be visible in some types of movements, like light trails.



Mar 03, 2017 at 01:55 PM
hokiejokey
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p.1 #6 · p.1 #6 · Multiple short exposures stacked = 1 long exposure without noise?


You will still have to deal with noise, no free lunch here.

What I never understood is what is the difference between stacking short exposures, and taking one short exposure and stacking it on itself (i.e. just moving the exposure dial to the right). If each exposure is 1 second, then each exposure should have the same information, or pretty darn close. So stacking them theoretically would just be the same as ramping up the gain, much like increasing ISO.



Mar 03, 2017 at 01:55 PM
AvianScott
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p.1 #7 · p.1 #7 · Multiple short exposures stacked = 1 long exposure without noise?


hokiejokey wrote:
What I never understood is what is the difference between stacking short exposures, and taking one short exposure and stacking it on itself (i.e. just moving the exposure dial to the right). If each exposure is 1 second, then each exposure should have the same information, or pretty darn close. So stacking them theoretically would just be the same as ramping up the gain, much like increasing ISO.


Because moving the exposure slider to the right doesn't smooth out water or allow for cloud motion for smooth skies, etc.



Mar 03, 2017 at 02:02 PM
jcolwell
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p.1 #8 · p.1 #8 · Multiple short exposures stacked = 1 long exposure without noise?


hokiejokey wrote:
What I never understood is what is the difference between stacking short exposures, and taking one short exposure and stacking it on itself...


AvianScott wrote:
Because moving the exposure slider to the right doesn't smooth out water or allow for cloud motion for smooth skies, etc.


Also, 'random' noise is always at the same locations (pixels) when you use one image for stacking on itself. Independent images, at the same exposure, will have very similar but slightly different noise.



Mar 03, 2017 at 02:06 PM
alundeb
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p.1 #9 · p.1 #9 · Multiple short exposures stacked = 1 long exposure without noise?




hokiejokey wrote:
You will still have to deal with noise, no free lunch here.

What I never understood is what is the difference between stacking short exposures, and taking one short exposure and stacking it on itself (i.e. just moving the exposure dial to the right). If each exposure is 1 second, then each exposure should have the same information, or pretty darn close. So stacking them theoretically would just be the same as ramping up the gain, much like increasing ISO.

Yeah, but the key here is removing the ND filter which makes each exposure contain much more light in addition to the same noise.



Mar 03, 2017 at 02:36 PM
hokiejokey
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p.1 #10 · p.1 #10 · Multiple short exposures stacked = 1 long exposure without noise?


I was thinking more for astrophotography, which won't have ND filter or water to smooth out.

I didn't think about the randomness of the noise, which will eliminate some the additive effect of noise from turning exposure knob up.



Mar 03, 2017 at 02:49 PM
alundeb
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p.1 #11 · p.1 #11 · Multiple short exposures stacked = 1 long exposure without noise?


Random noise will add up just as randomly in one long exposure as in multiple exposures, no benefit here.

Thermal noise, or hot pixels will show the noise in the same pixel for multiple exposures. This is the basis for how long exposure noise reduction, or black frame subtraction, works.




Mar 03, 2017 at 02:54 PM
jcolwell
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p.1 #12 · p.1 #12 · Multiple short exposures stacked = 1 long exposure without noise?


alundeb wrote:
Random noise will add up just as randomly in one long exposure as in multiple exposures, no benefit here.


...but noise will be increased by stacking many copies of a single image, compared to stacking multiple images or using one long-exposure image.



Mar 03, 2017 at 03:00 PM
RobDickinson
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p.1 #13 · p.1 #13 · Multiple short exposures stacked = 1 long exposure without noise?


stacking for noise reduction is a pretty well understood and used process


Mar 03, 2017 at 03:44 PM
woos
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p.1 #14 · p.1 #14 · Multiple short exposures stacked = 1 long exposure without noise?


dhphoto wrote:
A shorter exposure will be grossly underexposed, unless you opened the aperture or boosted the ISO, or both, not sure how that would work out


No it won't. :P

The OP said that for the shorter exposures he'd leave off the ND filter. So, that.

And yes OP. It works fine. If you are missing an ND you can just take a bunch of short exposures and average them. This works. It looks fine. No one will know the difference.

So, what's the downside? Well for one, at least on Canon, Nikon, etc (dunno about those fancy m43 olympus cams :P ) you can't preview the effect you'll get with your average later. So....yeah.

And yes, you can use this to get fake long exposures while handholding. But you'll need to zoom out and then crop after they are aligned.

I'm also unsure of what someone saying "just takign one image and stacking it on itself" would accomplish? Uhh....

You'd just end up with the original image if you stacked the same image on itself and averaged it. It wouldn't do anything. Maybe I'm missing what you meant. lol. That's like saying stack the number 2 and average it with itself. Uhhhh... I guess you can do that, but....all you will get is 2.



Mar 03, 2017 at 03:56 PM
RobDickinson
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p.1 #15 · p.1 #15 · Multiple short exposures stacked = 1 long exposure without noise?


downside is if you have a lot of foliage/unwanted movement etc then you are stuck to blending a short shutter shot in with the rest etc. Tho no different to the ND filter option.





Mar 03, 2017 at 03:59 PM
kirbic
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p.1 #16 · p.1 #16 · Multiple short exposures stacked = 1 long exposure without noise?


RobDickinson wrote:
stacking for noise reduction is a pretty well understood and used process


Indeed it is, and one I've used extensively. Random noise is reduced by the square root of the number of averaged shots, so if we use four exposures, we reduce noise by 50% (1 stop). This does not affect fixed-pattern noise at all. It neither makes it worse, nor better.
Also, the end effect of stacking multiple shorter exposures for a landscape will have the same effect from a motion standpoint as taking a long exposure. Again, I've used this on a number of occasions to enhance cloud motion, smooth water, etcetera.



Mar 03, 2017 at 04:02 PM
hokiejokey
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p.1 #17 · p.1 #17 · Multiple short exposures stacked = 1 long exposure without noise?


woos wrote:
I'm also unsure of what someone saying "just takign one image and stacking it on itself" would accomplish? Uhh....

You'd just end up with the original image if you stacked the same image on itself and averaged it. It wouldn't do anything. Maybe I'm missing what you meant. lol. That's like saying stack the number 2 and average it with itself. Uhhhh... I guess you can do that, but....all you will get is 2.


You can stack the same image on itself. You get a brighter version of the same image. And, as was pointed out to me, since the noise is effectively additive, you will magnify the noise.

Essentially the same as increasing the exposure in Lightroom.



Mar 03, 2017 at 04:13 PM
Daniel Smith
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p.1 #18 · p.1 #18 · Multiple short exposures stacked = 1 long exposure without noise?


Used to have ISO3 film available which made long exposure photography a lot easier.

WHEN will the makers give us the option of very low ISO settings on the digital cameras?



Mar 03, 2017 at 06:46 PM
RazorTM
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p.1 #19 · p.1 #19 · Multiple short exposures stacked = 1 long exposure without noise?


Daniel Smith wrote:
Used to have ISO3 film available which made long exposure photography a lot easier.

WHEN will the makers give us the option of very low ISO settings on the digital cameras?


D810 is as close as you can get without going to medium format, but it is apparently very good at low ISO.



Mar 03, 2017 at 07:33 PM
nandadevieast
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p.1 #20 · p.1 #20 · Multiple short exposures stacked = 1 long exposure without noise?


Guys what he says seems right. NDs: i got the point that one can stack multiple shots. But noise??
2 min exposure = 100+ short exposures but each of them will be dark, so not possible right?

dhphoto wrote:
A shorter exposure will be grossly underexposed, unless you opened the aperture or boosted the ISO, or both, not sure how that would work out




Mar 04, 2017 at 09:26 AM
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