Quote:
Originally Posted by PRejto
OK, what am I missing? How does a mount have anything to do with a flat field? Isn't a FF just a measurement of the optical system? So what if the FOV rotates during exposures. Dust and vignetting would be constant. It's just the illumination on the chip quite separate from what the chip sees as an imaged object that counts, no?
Last week I was at AIC and attended a lecture on flats given by Peter Kalajian. A question was asked about the contribution of dust on the objective to FFs. His response was that the dust was so out of focus as to not register. I would take that to mean that rotating the camera and filters would still give an excellent flat even if the objective/primary mirror were fixed. I think most rotators rotate everything following the focuser and not just the camera.
Maybe the confusion is about gradients. Those would rotate. I'm not sure how that might impact on removal. Perhaps not all all with the PIX tool.
Peter
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what about the tertiary mirror, that is quite a bit closer to the focus, but overall i agree, i dont see this as an issue