[Aavso-photometry] Flat Fields

[Michael Koppelman]

Flat fielding for one time series on the same pixels may or may not  
help that much but for different time series on different parts of  
the chip on different nights, it can make a huge difference, both in  
the high frequency stuff (pixel-to-pixel) and the low frequency stuff  
(vignetting, dust donuts). If your flat has, for example, a 10%  
gradient then you have a 10% error in un-flat fielded frames, whether  
you realize it or not.

So I believe it pays to just get in the habit and stay in the habit  
of calibrating your data.

M.


On Sep 12, 2007, at 8:52 PM, Wolfgang Renz wrote:

> Without good guiding and polar alignment or when just tracking or
> taking images in Alt/Az mode, the stars of interest will move across
> the chip. If the movement of the stars is just short, differences  
> due to
> vignetting might not be a major issue, but dust donuts might and
> severe pixel to pixel sensitivity differences will. It has happend  
> more
> than once that a star was suspected to be variable just because
> it moved across an anormal pixel during a TS.