The Large Fiber Array Spectroscopic Telescope: optical design of the unit telescope

Joel Berkson, Roger Angel, Chad Bender, Andrew Young, Peter Gray

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Scopus citations


The concept for the Large Fiber Array Spectroscopic Telescope (LFAST) (Angel et al, these proceedings) is to collect the light from a target object using thousands of individual, small, low-cost telescopes, and bring it via optical fibers to a high resolution (R=150,000) spectrograph. Each mirror has a prime focus corrector feeding a 17 micron fiber at f/3.5, subtending a 1.3 arcsec diameter on the sky. Each LFAST unit has 20 separate 30 inch telescopes carried by a single alt-az mount to provide collecting area equivalent to a 3.5 m traditional aperture. Each mirror has a 4-element corrector provides subarcsecond imaging over an 8 arcmin field. The field is reflected by a mirror puck (which contains the receiving fiber) through relay optics to a CMOS camera for rapid guiding and wavefront measurement. The corrector optical design incorporates elements of common crown and flint glass to obtain achromaticity over a broad wavelength range of 380 nm-1700 nm. Large, slow lateral translations of the final 4th element correlated with primary mirror tilt correct for atmospheric dispersion, and small, rapid lateral translations correct for image motion without significantly disrupting atmospheric dispersion correction. We have explored both aspherical and spherical primary mirror designs and have chosen spherical, based on impacts to unit telescope cost.

Original languageEnglish (US)
Title of host publicationGround-Based and Airborne Telescopes IX
EditorsHeather K. Marshall, Jason Spyromilio, Tomonori Usuda
ISBN (Electronic)9781510653450
StatePublished - 2022
EventGround-Based and Airborne Telescopes IX 2022 - Montreal, United States
Duration: Jul 17 2022Jul 22 2022

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceGround-Based and Airborne Telescopes IX 2022
Country/TerritoryUnited States


  • Large telescopes
  • atmospheric dispersion correction
  • optical design
  • spectroscopic telescopes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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