Re: [TASS] Flat fielding

["Borcher, David (NG-EX)" <DBorcher@GI.COM>]

                "...There was talk on this list maybe a year or so ago about
making
                some "integrating spheres".  This is a big hollow ball
painted
                flat white inside (special white paint)  There is a hole for
the
                lens to look in and another to let in a point light source.
For
                the Mk III the sphere needs to be about 18 inch diameter.
                There was another type of flat target suggested that used
multiple
                defusing screens."

- - - - -
I once saw someone use a sheet of very thick (about 1") white
"semi translucent" plastic, illuminated by incandescent bulbs
along each side.  I think the bulbs were a quartz halogen type.

He claimed that the light was completely diffuse along the broad
sides of the plastic sheet, and also that the illumination had to be
incandescent because LEDs or flourescent lights have such narrow
spectral characteristics.

The sheet was set atop the objective of the telescope when a flat
frame was to be made.  The illumination level was adjusted by means
of a variable-voltage power source.

I'm not sure how well this method really works, nor am I sure
how well it might adapt to a TASS system, though I can envision a
translucent shutter...

Just something to consider.

Dave Borcher
  Tucson  AZ