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Old 11-07-2014, 11:27 AM
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Originally Posted by Shiraz View Post
Software binning is possibly a better option overall - if you expose the 1x1 subs for long enough to bury the read noise you get all the advantages (and disadvantages) of bigger pixels - 4x the sensitivity, 4x the well depth and 1/2 the linear resolution.
Hmmm - the reason to bin in hardware is surely to get a reduction in exposure time or better s/n for the same exposure time (given you have small pixels and can trade away the resolution). Any software binning after the event is not going to give you signal that is not there (ie that is is lost in the background noise).

If we assume our CCD has a readout noise of 10e and out signal is twice that, then in the single pixel example each pixel is readout with a noise of 10e hence we achieve a signal to noise ratio of 2:1 (20e/10e). Even if we subsequently sum the four pixels in a computer after readout the signal to noise ratio becomes 4:1. In adding the four pixels we sum the signal (4 times 20e i.e. 80e) and the noise is added in quadrature i.e. square root of the sum of the noises squared (square root of 4 times 10 squared i.e. 20e). In the binned example there is no noise until the signal is readout by the amplifier so the signal to noise ratio is 8:1(80e/10e) i.e. twice as good as the single pixel readout mode.

Or at least that is my understanding....
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