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Multi-slit Improvements and Other Cryogenic Camera News (1Mar96)
(from KPNO, NOAO Newsletter No. 45, March 1996)

An option for multi-object spectroscopy at the 4-m telescope has been
the Cryogenic Camera or R-C Spectrograph with multi-slit entrance
masks. For many years we have been using masks made from photographic
film.

			Cryogenic Camera Grisms

Grism No.	  650    770     810     730   780-1  780-1  780-2

Order		    1      1       1       1       1      2      1

l/mm		  400    300     150     300     300    300    300

UDCW*(Angstrom)	 4950   5970    6360    8010    9700   4850   7100

Spectral Range	 4000   4000    4000    5600    7200   4000   4900
		-6900  -8400  -10500  -10400  -10300  -6300  -9700

Resolution	   12     15      30      15      15      8     15
(in Angstroms)

Angstroms/pixel	  3.2    4.3     9.1     4.3     4.3    2.2    4.3

* Undeviated central wavelength

We have now developed a new technique using thin etched stainless steel
for the mask material. This offers several improvements over the old
film method. The chief detraction of the photographic masks was a 10%
throughput loss in the film base material. Other problems, now
alleviated, were occasional scale errors due to drifts in the film
recorder electronics and internal fringing in the film base. All of
these deficiencies are now removed with the new blackened metal masks.
The only downside factor is cost and lead time. The new masks will cost
several hundred dollars for a typical observing run. For most runs,
with a reasonable number of masks, KPNO will absorb this cost. If more
masks for a run than the norm are requested, the observer may be asked
to share the cost. Since an outside vendor is doing the etching, the
lead time for receipt of the final mask patterns from the observer will
be increased to three weeks. There have been two successful runs using
the new material. Photographic masks will no longer be available.
Potential users are referred to the manual "Multi-Slits at Kitt Peak"
available via anonymous ftp from ftp.noao.edu or from the KPNO Home
Page http://www.noao.edu.

During recent runs the CryoCam has performed well and the reliability
has been excellent. The current chip, a Ford/Loral 800 x 1200 pixel
device with 15 um pixel size, offers good cosmetics with a readout noise
of ~15e-rms. Past instabilities in the readout noise characteristics
have been fixed. Above is a table giving the instrumental
specifications for the various grisms. Some grisms can cover more than
one harmonic in wavelength and users must choose their order blocking
filters with care.

Jim De Veny, Buell Jannuzi

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