Making a Sky Flat

The procedure to create a sky flat is similar to that mentioned above in Section 7.3.1:

1. Run an all-sky imaging sequence. A pointing model sequence as described in Section 5.4 works well, if taken when the moon is set.

2. Ensure that a present day 20 s dark is available. (This is the standard exposure length for the tpt pointing data).

3. Check the makeflat3 syntax. Here we will use it in a slightly different way.

   $ makeflat3

          Usage: makeflat -d flatdir [-f framenum -t datestr -r darkdir -n namestr -c]

4. Run makeflat3 on the data.

   $ makeflat3 -d /rotse/data/pipeline/image/ -t today -r /rotse/data/pipeline/cal/ -f 001 -n tpt

   We must specify that we only wish to use the first frame (001) of each pair. We do not want to use pairs of images, as the stars land on the same pixels in image pairs, thus biasing the median.