Design and performance of a F/#-conversion microlens for Prime Focus   Spectrograph at Subaru Telescope
  The PFS is a multi-object spectrograph fed by 2394 fibers at the prime focus of Subaru telescope. Since the F/# at the prime focus is too fast for the spectrograph, we designed a small concave-plano negative lens to be attached to the tip of each fiber that converts the telescope beam (F/2.2) to F/2.8. We optimized the lens to maximize the number of rays that can be confined inside F/2.8 while maintaining a 1.28 magnification. The microlenses are manufactured by glass molding, and an ultra-broadband AR coating (<1.5% for lambda=0.38-1.26 um) will be applied to the front surface. 
Naruhisa Takato, Yoko Tanaka, James E. Gunn, Naoyuki Tamura, Atsushi   Shimono, Hajime Sugai, Hiroshi Karoji, Akitoshi Ueda,...
astro-ph.IM