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 (Troy)]

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]

Originally Posted by 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.

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]

Originally Posted by Dennis

Hi Allan

Glad you worked it out.

Darks are subtracted.
Flats are divided.

Cheers

Dennis

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.