Quote:
Originally Posted by gregbradley
Couple of things.
You can do a false flat in Photoshop later if you have to.
Also when taking flats unless you have something sticking in the scope that creates an uneven illumination rotating the camera around makes no difference. The unevenness of illumination is vignetting and is usually symmetrical and turns with it. The scope itself is round.
I take flats at dusk with a white cloth over the lens or sometimes in the morning in a roll off roof with the roof closed, a white cloth over the lens and pointing at a dull wall slightly illuminated. Both work, dusk flats seem more reliable. At a star party that would simply leave dusk flats.
I find flats a bit of an art and now I never assume they are ok and test them on actual images to see how well they correct and retake them as needed.
I am finding the can be too bright and overcorrect but if too dark they don't correct enough.
If all you want to correct on this image is a tad of vignetting simply use the vignetting tool in lens correction in Photoshop or the vignetting slider in Lightroom or any other image processing program. They usually have a vignetting correction slider.
Greg.
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Thanks for this Greg.
I did know about the vignetting control in Photoshop and have used it regularly - can't remember if I used it or not on this image though.
I wasn't aware of the false flat in Photoshop however - I will have to check it out. I should get into the habit of taking dusk flats - particularly at star parties which is when I do a lot of my imaging. It wasn't an option on the night I took this however as it didn't clear till 8pm.