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Big Filters and Shutter for the Schmidt (1Jun93)
(from KPNO, NOAO Newsletter No. 34, 1 June 1993)

At present, the Schmidt CCD system uses a sliding filter bolt containing
2-inch x 2-inch slots and a small shutter, all recycled from the original 4-m
prime focus CCD system. With the 2048 x 2048 CCD (S2KA) that has become the
workhorse detector at the Schmidt, the corners of the chip are vignetted by
the filter and shutter assemblies. In addition, because there are no mechanical
stops (i.e. detents), filter positioning is not as repeatable as would be
desired, which occasionally leads to low-level flat fielding problems. In order
to overcome these difficulties, a new 4-inch x 4-inch filter wheel and shutter
are being constructed for the Schmidt CCD system. They will be copies of the
filter wheel and shutter in use at the 4-m and 0.9-m telescopes.  A dedicated
set of 4-inch UBVRI filters is being fabricated for the Schmidt, as well as
2-inch inserts for filters not available in the 4-inch size. The set of 4-inch
interference filters procured for use at the 4-m and 0.9-m will, of course, be
available for use at the Schmidt.

An added benefit of this system upgrade is that the filter position will, for
the first time, be readable and controllable from the CCD software (ICE). Thus,
Schmidt observers will find that their headers actually contain the correct
filter information, which will make processing the images much easier.
(Currently observers must manually edit in the filter position for each image
header.)

It is somewhat difficult to predict the completion time of this project due to
the sharing of resources between this project and other larger projects. At
present, December appears to be the most likely completion date. Watch the
Newsletter for additional information.

Taft Armandroff, Phil Massey

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