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7 March 2003 Optically-athermalized construction optical design for the IMACS short camera
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The optical performance of a large, optically fast, all-refracting spectrograph camera is extremely sensitive to potential temperature changes which might occur during an extended signle observation, over the duration of an observing run, and/or on seasonal time scales. A small temprature change, even at the level of a few degrees C, will lead to changs in the rerfractive indices of the glasses and the coupling medium, changes in the lens-element geometries and in the dimensions of the lens cell. These effects combine in a design-specific manner to cause potential changes of focus and magnification within the camera as well as inherent loss of image quality. We have used an optical design technique originally developed for the Smithsonian Astrophysical Observatory's BINOSPEC instrument in order to produce a construction optical design for the Carnegie IMACS Short camera. This design combines the above-mentioned temperature-dependent parameter variations in such a way that their net effect upon focus and magnification is passively reduced to negligible residuals, without the use of high-expansion plastics, "negative-c.t.e." mechanisms or active control within the lens cell. Simultaneously, the design is optimized for best inherent image quality at any temperature within the designated operating range. The optically-athermalized IMACS Short camera is under construction. We present its quantitative optical design together with our assessment of its expected performance over a (T = -4.0 to +20.0) C temperature range.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Harland W. Epps and Brian M. Sutin "Optically-athermalized construction optical design for the IMACS short camera", Proc. SPIE 4841, Instrument Design and Performance for Optical/Infrared Ground-based Telescopes, (7 March 2003);

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