Advice about taking flats

[shifter]

Is there anyone here that can help me with how to take flat images and how to apply them ?....Or if someone had already posted about this topic, can ya point me to it.......TIA......Brian

[MartinB]

Brian, flats are a chuffing pain. Only bother if you really need to - vignetting, dust bunnies. Probably the quickest and easiest is to get them at dust with a cloudless sky just before the stars start appearing. Point the scope at a clear bit high up and start exposing. Leave the tracking off to avoid having stars show up - you can then eliminate any trails by doing a median combine. The scope must be focussed perfectly on infinity - best left set from a previous session. The exposure time is important and is very dependent on your camera - basically you want to be at about 1/3 to 1/2 the brightness at which the pixels saturate which depends on something called full well capacity. As a rough rule of thumb an 8 bit brightness level of 128 in photoshop or 30 000 in Maxim will be fairly close.

The T - shirt method sounds straight forward as well. The only set up I have that needs flats is the NS8 with fastar and SXV H9 but since the camera is mounted on the corrector plate the T-shirt doesn't work! DSLRs usually need flats because the chip size makes them prone to vignetting.

How you apply them depends on your software.

here's a link with a lot more info http://www.iceinspace.com.au/index.php?id=63,211,0,0,1,0

Just remember though - only bother with them if you have a problem, they do degrade the image slightly.

[shifter]

Martin you're a star.... :thumbup:.... Yep I am gettin noise an stuff, its a pain, I'll get on to putting your advice into practice the first chance I get...thanks again.......Brian