ZWO ASI220 guide camera 12-bits vs 8-bits

[sarg314]

ZWO says that the A/D converter in the ASI 220MM guide camera is 12-bits.  I installed the 220MM using phd2 wizard.  Seems to work fine - just as I expected. But in the camera page PHD2 shows it saturating at 255, not 4095.  I assume the wizard knows the camera specs for this common camera correctly.  Is it using the high order 8 bits of the 12-bit  data or do I need to change something?

[Bruce Waddington]

It can depend on what driver you're using - native or ASCOM - and whether it can operate in either 8-bit or 16-bit mode.  The next time you're set up for guiding, start looping, select a saturated star, open the Star Profile tool, and look at what the peak value brightness value is. If the driver you're using allows you to specify 8 or 16 bit operation, 16-bit is likely to be a better choice.  I think the ZWO drivers normally scale the data to either 8 or 16-bits before returning the image to PHD2.  The important thing is to avoid having a saturation-adu value that is too low for the actual data.

Bruce