weird pattern from bias integration

[cosmochristo]

Hi, I am new to pixinsight and have found integrating bias frames gives a strange pattern (see attached). Frames taken using a canon 5D III, 8-15mm fisheye lens at 11mm. They have been converted to tiff images using Canon's DPP. iso 50, 1/8000s.

[cosmochristo]

I think I know: All images I converted to tiff using the same operations as on the light frames and that included the distortion correction operator. Looks like the one thing I should not have done!

[Greg Schwimer]

Well....

With bias frames, what lens you have on there should not matter. In fact, the shutter should be closed. You could conceivably grab bias (and dark) frames with the camera completely detached from the optics.

What software, exactly, is correcting optical distortion on a bias frame that should never see light from any source?

Maybe don't use whatever is doing that and stick with PI for the very early preprocessing of the data.

My $2e-02.