|
Yep, differences in stellar profiles are almost inevitable if you image across different nights (seeing) or you have to refocus often or at a filter change. These days I don't have to refocus but of course seeing across multiple nights is still a pain.
My standard workflow includes zooming in on a non-saturated star that's as close to G2V as possible and decon'ing until the stellar profiles in R, G & B for that star are about the same. It's usually possible to spot G2V (or close to) stars in good images of the same field from other people - they should appear white. You can also wing it and examine your own raw RGB combine for non-saturated white-ish stars but that requires that you do a reasonably accurate combine. I've had luck doing my raw RGB combines by looking only at an isolated star field in the frame (ie zoomed in). Green stars are a no-no, background should be neutral and star colours should appear natural (eg red, white, blue and yellow). After you get that about right, decon to normalise on a white-ish star. The limitation of decon'ing of course is the amount of decon you need to do. If the seeing was particularly bad for one filter but not the others, decon artifacts may be unsightly.
Cheers, Marcus
PS: I've even been known to blur a sharp colour channel to achieve consistent stellar profiles since I usually layer a slightly blurred RGB layer to luminance anyway (in Photoshop).
|