Re: [TASS] Flat fielding

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

On Thu, 9 Sep 1999 22:29:46 -0500, Tom Droege <droege@WWA.COM> wrote:

>The flat fields were definitely not up to snuff.  I don't even have any
>good idea about how to make a good flat field for the Mark IIIs.  You
>cannot make twilight flats with a device that takes a 470 second long
>exposure.  At twilight the conditions are changing much faster than that.
>You can't point it at a "dome flat" spot because it does not point.

If the camera won't turn to point at the dome, the dome must turn
to point at the camera.

>  You
>just have to look at the data and use that.  This is what Mike G's program
>does.  I think that this is all one can do.  I think Mike went to a lot of
>effort to think of the best possible way.
Yes indeed! Simple and elegant.

But if the N-S illumination gradients are really putting in
5% variations in sensitivity ...

How big are the variations in average sensitivity from
column to column, assuming a minimal population of
dust bunnies? Is most of it lens vignetting rather
than CCD?

******** heretical matter follows *********************
Could it be that one would be better off in a drift-scan
instrument not doing flat correction at all?
******** end of heresy. You may open your eyes now ****

Andrew Bennett, Avondale Vineyard, Nova Scotia, Canada.