Does the ISO matter when taking flats?

[Bizibilder]

I normally do DSO imaging with my modded Canon 1000D at ISO 800.  Does it matter if I take my flats at a different ISO setting?  I use a lightbox and set the camera to ISO 800,  Av mode, and just snap away - seems to work.  As far as I know Flats are just a "brightness" that is subtracted form your Lights so it shouldn't matter - or am I confusing things again??  Hope you can help.

[Alien 13]

Like you thought It does not matter, in most cases a DSLR will be in AV mode or similar so it will adjust whatever to get the correct exposure.

What can effect it though is shutter speed, if its very fast because of a bright sky etc you can sometimes get a shadow at the bottom of the image.

Alan

[dph1nm]

I would take some bias at the same ISO as the flats - just in case (you need to subtract the bias from the flats in order for them to work properly). Flats are divided into the lights not subtracted by the way.

NigelM