Help with flat frames.

[allan gould]

I need some help with my flats. I started to take some flats after noticing dust bunnies on my DSI II pro camera. Th exposure was quite low as I used the white T shirt method as I havn't built a light box as yet. However when I use it with my stacked images I loose all detail in my image and wind up with just the brightest stars. I used DSS to manipulate my images but what should I be doing with the flat and what software? Is there an idiots guide for photoshop manipulation?
All help very gratefully received.

[allan gould]

Dont worry - figured out how to do it with photoshop. What a difference taking a flat frame makes in removing setup artifacts as well as those (*!#$%!(* dust bunnies

[Dennis]

Hi Allan

Glad you worked it out.

Darks are subtracted.
Flats are divided.

Cheers

Dennis

[troypiggo]

Allan, if you're using DSS I don't think you need to do it in PS. DSS handles flats natively. You load them with the buttons near where you load lights and darks.

[allan gould]

DSS behaved quite badly as after putting in the darks, bias and flats all I wound up with was the 4 brightest stars. Go figure.
I must have done something wrong as usual, but PS is a real winner.

[CoombellKid]

Hi Dennis

Is there any "How To's" on how to do this in Photoshop 7

Cheers,CS

[Dennis]

Hi Rob

Whoops! Allan may have to answer this one, as I use CCDSoft and MIRA AP for Darks and Flats reduction!

Cheers

Dennis

[allan gould]

Took a while to figure out as first you collect a series of flats and flat darks. Median combine all frames and make a master flat and master flat dark. Subtract the MFD from the MF and then bring up the median combined master light frame. You then do a "calculation" in PS, but since it doesn't have a divide function but only a multiply function you have the lights and flats in the calculation format, invert the flat and then "multiply" the inveryted flat into the light. Voila, dust bunny contraceptive - no more "bunnies" or vignetting. There's a lot in AIP about flats but it goes into the maths which I didn't want - I just wanted a simple procedure that was universally aplicable that I could control.