Master Flat Frames?

[sreilly]

What is considered a good number of flats to use to make the master flat. I've been using 72 with 36 for east and 36 for west side flats. Do I need this many or is there any advantage to more or less? I usually use 40-50 bias frames and 30 or more same temp/time darks for the master dark and bias frames.

Suggestions on best practices?

Thanks,

[RickS]

It depends on the characteristics of your camera.  For my camera, an Apogee U16M with KAF-16803, I target a total of 500K electrons (which is the point of diminishing returns according to a flat field PTC analysis.)  My full well is around 80Ke-, so at an ADU value in the middle of the range that's only 12 flats.  If you have a camera with shallow wells it will almost certainly be a much bigger number.

Without doing the PTC calculation, something around 30-40 flats sounds like a reasonable number for a sensor like the KAF-8300 (25Ke- well depth.)  You could always use the PI tools to do a noise analysis as you add more flats to your master and see where the improvement starts to drop off.

Cheers,
Rick.

[sreilly]

Thanks for the reply Rick. I guess I should have mentioned the camera is a STL-11002M and the other ST10-XME. Full well of the 11002 is 50,000 ADU and 77,00 for the ST10. I must say I haven't analysed the flats. So what is this PTC analysis?

Steve

[RickS]

Steve,

Gory details are described here: http://www.narrowbandimaging.com/incoming/flats_part1_part2_part3_expanded.pdf

Cheers,
Rick.