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Old 04-12-2015, 10:53 AM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
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John
Calibration with CMOS cameras may be a bit different. Instead of a single A/D, you have one for each column, which means that you can get fixed pattern noise due to slightly different bias on each A/D. My limited understanding is that at least one manufacturer (Aptina) fixes this by doing a chip calibration at power up and this equalises the A/Ds to remove fixed pattern bias noise. An unwanted outcome of this process can be that each time the chip powers up, you end up with a slightly different bias set, since the process never converges to exactly the same solution. Thus, you will need a new bias calibration for each time you switch the camera on. I don't know if Sony does the same, but they must do something to fix the problem - bear it in mind when trying out calibration processes, since variable bias will need careful handling. Maybe ZWO can provide some advice on calibration - might head off an ulcer.

Because the chips are quite low noise and so small that vignetting will not be an issue, it might be a reasonable approach to dispense with calibration altogether (probably need bias subtraction though) and rely on dither to randomise any residual fixed pattern noise so that it integrates out. If doing lucky imaging, you will have enough subs for this to work well.

Torsten's on-the-fly calibration sound promising - if you use it, suggest that you employ as many darks and flats as the software will allow (more is always better)

Last edited by Shiraz; 04-12-2015 at 04:23 PM.
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