How do you do flat frames (with DSLR)?

[Daveskywill]

Hello:

I was wondering if it would be alright to use a small C-battery powered lamp that uses a flouresent light and a diffuser filter in the front as a source for flat frames.

(Particularly for my Canon Rebel T2i DSLR)?

And are you supposed to do this with a lens on?

Or do you leave the lens off and place the source up to the front
of the camera body. And for how long should the exposure be?

PS: I'm considering buying the latest version of Starry Night Astro Photo Suite. So then I could practice my skills.

But does someone here know about Maxim DL? And if that would or could be used for subtracting dark frames and doing what you do with flat's?

Thank you.
David

[Poita]

I don't really know, but I'll soon be attempting the same thing myself, so I'm keen to find out.

I did find this: http://astroromp.com/astronomy/shooting_flat_frames.htm
not sure if it is good advice or not though!

[mswhin63]

Flats need the imaging equipment (lenses and telescope) to be connected when taking each of them. This takes into consideration any distortion produced by the lens including on some occasion dust spots.

[rcheshire]

I take flats using a laptop screen. Possibly not optimal, but they work. Create a new white frame in Photo shop or equivalent. Focus on infinity (should be already as flats are usually taken after an imaging run) keep the f/ratio the same as your images, set the lowest ISO and shutter speed about 1/10 second (that way you wont have to dark calibrate your flats), then adjust screen brightness to give a zero exposure.

Now hold your lens close - I usually have the lens hood just touching the screen - its and old laptop - alternatively, place a sheet of A4 or a tissue between the lens hood and screen keeping it flat. Adjust screen brightness as required and fire away.

Or - these are reputed to be excellent.

http://www.iceinspace.com.au/forum/showthread.php?t=49736&highlight=light+boxes