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Session 54 - Ground and Instrumentation Techniques and Catalogs.
Display session, Wednesday, June 12
Tripp Commons,

[54.06] Outrageous Camera Lenses for Two New Keck II Spectrographs

H. Epps, B. Sutin (UCO/Lick Observatory)

We have produced optical designs for two new spectrographs currently under construction at UCO/Lick Observatory which will be used on the Keck II telescope. The first is DEIMOS, a dual-field areal spectrograph with a single on-axis reflecting collimator and two huge 15.0-inch f/1.29 wide-field broad-passband refracting cameras. The second is ESI, a single-beam prism cross-dispersed echellette spectrograph using an off-axis reflecting collimator with an even faster 12.1-inch f/1.07 broad-passband camera. Since our unique camera lens designs make these spectrographs possible, we present them here in some detail.

The DEIMOS camera has a doublet/singlet/triplet/doublet/singlet configuration with 3 aspheric surfaces. The 22.8-degree field diameter produces a 6.05-inch flat field of view. This design shows rms image diameters of 23.2 +/- 7.1 microns averaged over all field angles and wavelengths within a (0.39 to 1.05)-micron range without refocus, with only 35.6 microns of maximum rms lateral color. Thus, sub-arcsec (B,V,R,I)-band imaging as well as spectroscopy will be possible at the 126-micron/arcsec final imaging scale. A flat 0.50-inch thick fused silica dewar window preceeds the (8K x 8K, 15-micron) CCD detector mosaic.

The ESI camera has an all-spherical doublet/singlet/triplet/triplet configuration whose 13.0-degree field diameter produces a 2.76-inch flat field of view. In this design, the elements of the leading doublet are reversed relative to DEIMOS, and the trailing triplet combines with a plano-concave fused silica dewar window. This camera shows rms image diameters of 18.3 +/- 4.8 microns averaged as above over a (0.39 to 1.09)-micron passband without refocus, with 24.7 microns of maximum rms lateral color. Echellette orders (6 through 15) will present that entire passband to a (2K x 4K, 15-micron) CCD detector in a single exposure, without any spectral gaps.

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