A 1-degree FOV 30-meter telescope concept revisited

Samuel C. Barden, Andrew McGrath, Peter R. Gillingham, Charles F.W. Harmer

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Citations (Scopus)


The science case for wide fields on ELTs is well developed and justifies the implementation of 20 arc-minute and larger fields-of-view with seeing-limited performance on a 20 to 30-meter telescope. However, the practical implementation of a wide field can prove to be challenging with classical telescope design when low-thermal emissivity performance is also being optimized. Segmented mirrors assemblies need not be full aperture, axially symmetric structures. Space for secondary, tertiary, and quaternary mirror support structures that do not cross the optical path can be achieved with off-axis mirror assemblies. Barden, Harmer, Claver, and Dey1 described a 4-mirror, 1-degree FOV 30-meter telescope. We take that concept further with an off-axis approach. Three conic mirrors are required to produce excellent image quality in the 1-degree FOV (diffraction limited across the central few arc-minutes, better than 0.3" imaging performance at the edge of the field). A flat quaternary mirror is utilized both as a beam steering mirror to different instrument ports on the lower side of the telescope and as an adaptive mirror for wind-buffeting and possible ground layer AO correction. The final f/2.2 focal ratio allows the use of an echidna-style fiber positioner for very dense target field acquisition. Extreme AO and Ground Layer AO ports can both be implemented as well. Diffraction characteristics may possibly be improved given the lack of a spider mount for the secondary mirror but will be elliptical rather than circular.

Original languageEnglish
Title of host publicationGround-based Telescopes
EditorsJacobus M. Oschmann Jr.
Number of pages8
Publication statusPublished - 2004
Externally publishedYes
EventGround-based Telescopes - Glasgow, United Kingdom
Duration: 21 Jun 200425 Jun 2004

Publication series

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


ConferenceGround-based Telescopes
Country/TerritoryUnited Kingdom


  • ELTs
  • Multi-object spectroscopy
  • Optical design
  • Telescopes
  • Wide-field


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