Quote:
Originally Posted by alpal
My method to take flats:
I use my 27" LCD monitor with the screen made all white in Photoshop.
I put the Newt. on 2 pillows - a white T shirt taped across the front aperture.
I make sure the camera has not moved in rotation or focus.
I put the monitor about 2 feet away from the front aperture
& line it up to be central.
I turn all the lights out & put a black T-shirt over the camera
but not on the heatsink - to stop stray light getting in.
I also block the bottom end of the Newt. with a cover & black cloth.
I bring the camera to the correct identical temperature.
( probably not necessary)
I then take short exposures to go to about half the 16 bit brightness
for all LRGB & Ha filters - 3 frames of each.
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Sounds good. Taking flats at the same temperature I would regard as quite important. When I had an Apogee U16M the really slow cooldown time used to cause me grief. I would inevitably leave it to dusk to setup for flats and the light would be failing yet the camera took 40 minutes to cooldown. In that time the flats I did take were useless as they were too warm and the noise levels way too high.
You are referring to a DSLR I am sure but regardless it would be best practice to match the temperature. With most CCD if you look at their data sheet they typically double the thermal noise with every 6C rise in temp. That would be true for DSLRs as well. So if you took images at night in 10C and then took flats at 25C at dusk you may not get ideal results.
Per Richard 3 is not enough so I plan to increase the number of flats I take. It may be worthwhile to take more and compare results with yours as well.
Greg.