Reply To: Bias Frames for CMOS

Forums Photometry Bias Frames for CMOS Reply To: Bias Frames for CMOS

Graeme Coates

As Ian says above, taking matching darks, flats and matching flat darks with the same temp, gain and offset is all that’s required (in my experience, taking and trying to apply bias frames makes everything *much* worse – I fell into this trap when first starting with a CMOS camera…).

On a practical point of view, it’s useful to pick two gain/offset combinations – one for broadband imaging with low gain, and one for narrowband with high gain (you need a bit of work to determine offset to ensure you don’t clip the pixel values at the lower end through insufficient offset) – then stick with them, and a few exposure times – these again should be determined to ensure the sky background noise swamps read noise. This makes taking calibration frames much less onerous, and with set point cooling, (the darks at least) can be reused for some time if you have set point cooling.