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Originally Posted by tornado33
thanks all
getting a flat field over a wide area is tough, as the bottom of the frame is in brighter light pollution than the top. I think also the filter is sensite to angle of incidence, so light coming in from the sides is altered differently than light in the middle which hits the filter at right angles.
Scott
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Hi Scott,
Although I agree that much of the gradient in your shot is from LP, there also appears to be a degree of vignetting. How I deal with this is to make up a master flat by placing a white tissue over the lens and taking about a dozen shots in "P" mode. Applying these flats does make a difference to widefields. Of course there is still the LP gradient to deal with.
I put your jpeg through a little program called ABE. It did a reasonable job of removing the gradients. After that I readjusted the levels. I had to make a slight adjustment to the colour balance in the top left and this is the result:
Cheers