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Re: tn89

It takes a lot of layers.  Particularly if you are trying to use the same 
exposure length for the flat field.  I have done something similar.  I 
built a light box.   This consists of a light, a white screen in a black 
tube, followed by a white box.  The idea is that the first screen provides 
a large area that is fairly uniform.  This illuminates one side of the 
white box (made from good white paper).  Light from the screen illuminates 
one side of the box.  The light that enters bounces around in the white box 
and then illuminates the far side which is facing the telescope.  The idea 
is to produce something similar to a sphere.

Tom Droege



At 01:43 PM 1/1/03 +0000, you wrote:
>...following the flat-fielding discussion, has anyone tried creating
>flat-fields using the daytime sky by covering the aperture with a screen
>made of the appropriate number of layers of white fabric? I am just about to
>try this, so would be interested to hear if it is an appropriate method to
>use.
>
>Karen Holland
>
>
>----- Original Message -----
>From: "Arne Henden" <aah@nofs.navy.mil>
>To: "TASS List" <TASS@listserv.wwa.com>
>Sent: Tuesday, December 31, 2002 5:42 PM
>Subject: tn89
>
>
> > Michael and Tom,
> >    The main problem with the technical note is the procedure for
> > flatfielding.  Here, the data frames were combined to create
> > a master sky flat, which was then applied to the data.  Master......