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Old 12-09-2011, 07:09 AM
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Stacking Movie

As an exercise to see how many frames I needed to collect. I made an animated gif of increasing numbers of stacked cropped frames. These stacked frames have been upsized by a factor of 6.4.

1, 4, 9, 16, 25, 36, 49, 64 and 81.

In theory the signal to noise is improved by a factor of the square root of the number of frames. This only applies to the Poisson or statistical noise not 'noisy' or 'hot' pixels.

Here is a small version 900kB

http://d1355990.i49.quadrahosting.co...amestestsm.gif

For a better effect here is a large one 23MB

http://d1355990.i49.quadrahosting.co...amestest02.gif

The exposures were for 60s at an ISO of 1600 and dithered. All were corrected with darks and flats.

It is a very clear demonstration of how useful stacking is to reduce noise and thus enhance signal.

The very dim stars appear out of the noise as if by magic. The major factor here is the dithering as inherent residual sensor noise is not enhanced.

Bert
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Last edited by avandonk; 12-09-2011 at 08:19 AM.
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  #2  
Old 12-09-2011, 08:07 AM
adman (Adam)
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thats a nice way to display the effect of stacking. The most noticeable / useful reduction in noise seems to occur between 16 and 25

Adam
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Old 12-09-2011, 12:02 PM
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Osirisra (Ken)
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awesome! great way to show people what stacking does.
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Old 13-09-2011, 04:32 AM
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Thanks all for the comments.

Here is an animated gif made with 240s exposures same conditions as the 60s.

Again 1, 4, 9, 16, 25, 36, 49, 64 and 81 frames stacked. 1.5MB


http://d1355990.i49.quadrahosting.co...rtest240s_.gif

It is obvious that after about 25 frames there is not much improvement.


This is an animated gif of a stack of 64 frames at 60s and stack of 16 frames at 240s. 5MB

http://d1355990.i49.quadrahosting.co...9/timecomp.gif


This shows that in this universe there is no free lunch. Nothing beats more photons.

This tells me for this configuration at least 60 minutes of data should be collected whatever the exposure is, to attain a reasonable signal to noise ratio.

Hope this little experiment shows to all of us that the theory is true.



Bert
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Old 13-09-2011, 04:33 AM
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Here is the 81 frame image.
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