[TASS] Flat fielding

[Andrew Bennett <andrew.bennett@NS.SYMPATICO.CA>]

In TN0019 (960903) Michael Richmond wrote:
> I made a flatfield vector for each segment by
>calculating the median value of pixels in each
>column. I then divided each image by this 1-D
>vector. After looking at some of the reduced
>images, it appears that I'll need to find a
>better way of calculating the flatfield vector;
>this method can be screwed up by bright stars and
>changing sky brightness.

To which Herb Johnson in TN0057 (Aug 19 1999) added
>[The image should be a twilight image of a
>high and relatively uniform illumination]

Ah! It should be. But is it? Are all the
flatfield images up to standard? Or could this
be a major contributor to the 0.05 magnitude
noise floor?

In other contexts, the importance is stressed
of averaging as many flatfield determinations
as possible. As far as I can see, our software
does not allow for averaging. Should it?

Andrew Bennett, Avondale Vineyard, Nova Scotia, Canada.