[Aavso-photometry] Dark-subtracting flat frames

[Michael Koppelman]

I think you want to dark subtract each flat and then combine the flats.

Yes, for science, we don't cut corners and you absolutely should dark 
subtract your flat fields. Pretty picture people don't care about 
anything except pretty. Scientists seek to remove or reduce every 
possible systematic source of uncertainty.

Cheers,
Michael Koppelman
http://www.lolife.com/astronomy/



On Jan 11, 2005, at 8:48 AM, Greg Crawford wrote:

> In the world of pretty picture imaging there is some discussion about 
> not
> needing to dark-subtract flat frames. I wonder how well this applies to
> photometric imaging?
>
> I normally operate an ST9E at -20C and take flats frames of 2 seconds 
> duration
> for V,R & I; and 15 seconds for B. My normal routine is to do 32 flat 
> frames per
> filter and median combine each filter's flat frames, then dark 
> subtract a master
> flat-dark made from either 32 x 2 second dark frames (for V,R, & I), 
> or 32 x 15
> second dark frames (for B).
>
> Am I adding noise to the master flats, wasting my time, or improving 
> the quality
> of my photometry?