The development of Binospec and its optics

摘要

Binospec is a binocular optical spectrograph under development for the converted MMT. Binospec addresses two adjacent 8′ by 15′ fields of view, yielding an effective slit length of 30′. Despite its very wide field of view, Binospec's optics are compact due to the favorable image scale at the converted MMT's f/5 Cassegrain focus. However, Binospec's all-refractive collimator and camera have presented several challenges, including the need for careful athermalization and high performance optics mounts. In the course of Binospec's development H.W.E. and D.G.F. developed a new athermalization technique to maintain image scale, image quality, and focus over a wide temperature range using thin lenses formed in the coupling fluid between lens multiplets. Tight, specifications for image quality and gravity-induced image motion and defocus lead to tight specifications for displacements of Binospec's optical elements. We describe how Binospec's elastomeric lens mounts have been tuned to attain this level of performance.