Stopping down the I-band camera

[Michael Richmond <richmond@stupendous.cis.rit.edu>]

> 6) Stop down the I telescopes.
> 
> I have not settled this for sure yet.  The I cameras see about twice the
> sky background as the V cameras.  Stopping down to a 3 inch aperture makes
> the sky background about equal.  I have tried this and the I focus is
> clearly better.  Possibly I will cut masks at 3.5" and compromise.  Get a
> little better focus and a reduced sky background.  Still testing.

  It would be interesting to take and compare two datasets on 
two different nights:

      a) aperture wide open -- look at several tiles repeatedly.
              Reduce the data with the standard synthetic aperture
              size in the pipeline.

      b) aperture stopped down -- look at the SAME tiles repeatedly.
              Reduce the data with a smaller synthetic aperture
              size in the pipeline.

  If the focus is improved by stopping down the aperture, it may
be possibly to dig down almost as far into the noise in both
sets of exposures.  Using a smaller synthetic aperture in the
measuring procedure will include a smaller amount of sky background,
and the sky background will be smaller, too.   

  So, Tom, if you were to look at the same regions of the sky
on two nights, then compare the "sigma-versus-mag" plot
for each night, you might have a quantitative basis for
making the decision to go with or without an aperture mask.

                                Michael