[Aavso-photometry] Flat Fields

[Jeff Hopkins]

I have been experimenting with flat fields. Everyone has said to get 
the best data you must flat field your image.  Has anyone actually 
done experiments to show how important this is?

In my experiments I have found that there is less than 0.01 magnitude 
difference between photometric data taken from original images versus 
those calibrated with flat fields.

Taking flat fields is a major effort and extra work in processing. 
While it is nice to get rid of dust donuts, just how much does it 
affect the photometric data to flat field the image?

The theory sounds fine, but in reality I have not found that it makes 
much difference. Taking three 10 second images in a given filter with 
darks subtracted produces 3 original images. Flat fielding them and 
comparing original image 1 to image 1 flat fielded show magnitude 
differences of less than 0.01.

Comparing image 1 to image 2 and image 3, I see greater than 0.01 
magnitude variations in both the original set and the flat fielded 
set. That makes me think that perhaps the flat fielding benefit is in 
the noise.

I am still experimenting and am not please with the flat fielding 
I've done. I have tried light box, dome and twilight flats. Either I 
am doing something wrong or this seems to be a wasted effort.

I'm curious if anyone else has experimented and determined empirical 
data on the value of the flats.

Thanks.

Jeff
-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
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