Quote:
Originally Posted by Satchmo
Steve
So as the raw image projected on the CCD chip is 4X as bright on the F4 and an F8 scope, won't the brightest parts of the object fill the CCD pixel to full well capacity much faster . So if you can get more exposures in doesn't more stacked images that are at full saturation mean better signal /noise ?
I'm on a learning curve here , but this is one hurdle I'm not over yet...
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Hello Mark,
Before the pixel reaches saturation, the signal and noise increase by the same factor hence S/N ratio remains the same where the noise is purely confined to photon noise. That's because you're not actually increasing the total signal, instead the signal is distributed over a smaller number of pixels.
When a pixel reaches saturation it's impossible to measure the S/N ratio. The photon noise is the standard deviation of a series of measurements of a given pixel over a number of exposures. When a pixel reaches saturation it has reached its maximum value.
When the signal is increased by exposure time or by increasing aperture, the signal and noise increase at different rates.
By quadrupling the exposure (or doubling the aperture), the signal increases 4X but the noise increases by only 2X.
Hence the S/N ratio doubles.
Regards
Steven