Stacking photos

MatBin

MatBin

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matt
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Help, idiot question coming up.
I understand that if I take numerous photos of a night sky scene using different exposure times and stack them I will see details that a single exposure would not have captured e.g. a 1, 3, 10, 30, 60 second group of photographs (5 exposures in total) of the same scene stacked (maybe a shot of a planet for example) will show more detail than any of the single photographs would have shown on their own - I get that.

However, I dont see the point of doing the same thing but taking many shots all with the same exposure e.g. as before but 10 shots at 1 second, 10 shots at 3 seconds, 10 shots at 10 seconds etc. Surely all I will have is a group of identical shots with identical detail. For each group of shots, for exampl the 1 second shots will surely all contain the same detail as each other, all the 10 second shots will be identical to each other.
What's the point of taking multiple identical shots and stacking them?

Matt
 
I'm sure someone with more knowledge than I have will be along soon but as I understand it the more photos you stack, the more information (light) is gained.

There fore if you have 10 1 second exposures the stacking software adds them all together to enable you to see much more detail than 1 single exposure.
 
Signal to noise ratio and dynamic range. Take one 10 min exposure and you'll lose detail due to noise as well as saturating any bright areas. Take 10 1 min exposures and stack them and you have effectively a 10 min exposure but with far less noise therefore far more detail, in both bright and faint areas. Another advantage is that assuming you are using a tracking mount, there will be some inaccuracy in the tracking, so keeping individual exposures short gets round any problems that creates. If you are imaging through a telescope for anything more than about a minute you need to guide the scope to avoid trailing (the exact cutoff time depends on the size of the scope and how well it's polar aligned). In the days when dinasaurs still walked the Earth I used to take 45 min exposures on slide film, manually guiding the scope to correct the drive. Occasionally I got a decent image. I physically could not do that now. Now you set up a web cam and software and let the computers do it for you. By the way there's little point in taking multiple shots for stacking at different exposures very close together in length. However if you are imaging, for example, something like the Orion Nebula which has extremely bright areas and extremely faint details you can take stacks of very different length exposures and use something like HDR to combine them, depending what software you use.
 
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You are describing an HDR approach and, yes, more details of
the scene will be recorded if your meter says 4 s. and your se-
quence is 1, 2, 4, 8, and 16s for ex. The process is done through
the HDR tool of your software.

The reason behind shooting some three copies of the same expo-
sure is in case there are moving parts in the subject, like people or
else. Having copies makes cloning out these much easier. Once
all thirty have been reduced to the desired ten, just process them
with the HDR tool.

Have a good time!
 
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