SharpCap Forums

Greetings all. I've watched Robin's excellent youtube video on CMOS imaging several times to really try to get an understanding of how different kinds of noise impact optimum sub exposure calculations. One question remains that I'd appreciate input on. How do I treat binning in the calculation of optimum sub exposure length? Since the pixel dimension is required to calculate the noise due to light pollution, I'm not sure how to treat binning in the sky background noise calculation. If I assume I am binning 2 x 2 do I use the dimension of that larger frame as the pixel size used in the sky background calculation? For example, my camera has a pixel dimension of 4.63 microns. If I'm binning 2x2 do I put 9.26 microns into the formula? I assume so, but after watching the video several times, I know its not always intuitive. Thanks for any input!

Allan Staib

Hi Allan,

A good question – I had to go and check the code before being able to answer.

I think you should use the raw pixel size of the camera - 4.63 micron - for the calculation and into that value into SharpCap. The values displayed to the user in the brain window are all adjusted to remove the effects of any applied binning. The same applies when you are entering the sky brightness using the drop-down.

The key is that the recommended exposure time shouldn't change for CMOS cameras when you apply binning. This is because the binning for CMOS cameras it is always done digitally by adding pixel values after they have been through the ADC. For CCD cameras (if SharpCap knows it's a CCD camera) you should get a shorter recommendation when you apply binning because charges from each binned pixel are added together before being sent to the ADC - this reduces the effect of read noise on the final value.

Cheers, Robin

Thanks Robin! Great software!