Quote:
Originally Posted by cometcatcher
Be cool to see a comparison Cam. I've been eyeing this filter for some time but it's not a cheap one.
As for gradients, I have them also. Many of mine appear to be on the CMOS sensor itself. It has a green / magenta cast to it right through the middle of the frame. Flats, darks and bias do nothing to remove them. I have to software flat field every image I take.
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I've imaged everything now that I have easy access to at this time of the year so if I get another decent night I'll take one without the IDAS. I got mine 2nd hand so only paid about $100 for it.
The gradient is NOT on your sensor - if it was then the flats would fix it. Flats, darks and bias won't affect anything that's in the sky, just in the optical train.
I get the green/magenta thing too, and where it occurs on my images and how far across them depends on where I'm imaging in the sky and how much movement/rotation there is relative to the light pollution. Dealing with gradients is sadly a core skill for the astrophotograhper these days. My new technique is to duplicate my image twice. Blur one very strongly (150+ pixels), darken it and subtract it from one of the the others. Now use your original as a colour layer on your corrected image - adjusting opacity to suit. The bright colours will stay, the dark background will be too dark for you see the colour difference. You've effectively neutralised the luminance and recoloured, but it's a bit more gradual.
