8 September 2011 Range-balancing the Large Binocular Telescope
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Abstract
The Large Binocular Telescope (LBT) consists of two 8.4 m telescopes mounted on a common alt-az gimbal. The telescope has various modes of operation, including prime-focus, bent- and direct-Gregorian modes. The telescopes can feed independent instruments or their light can be combined in one of two interferometric instruments, giving an interferometric baseline of over 22 m. With all large telescopes, including the LBT, collimation models or modeled values for hexapod positions, are required to maintain reasonable optical alignment over the working range of temperatures and telescope elevations. Unlike other telescopes, the LBT has a highly asymmetric mechanical structure, and as a result the collimation models are required to do a lot more "work", than on an equivalent aperture monocular telescope that are usually designed to incorporate a Serurrier truss arrangement. LBT has been phasing in science operations over the last 5 years, with first light on the prime-focus cameras in 2006, and first light in Gregorian mode in 2008. In this time the generation of collimation models for LBT has proven to be problematic, with large departures from a given model, and large changes in pointing, being the norm. A refined approach to generating collimation models, "range balancing", has greatly improved this situation. The range-balancing approach to generating collimation models has delivered reliable collimation and pointing in both prime focus and Gregorian modes which has led to greatly increased operational efficiency. The details of the range-balancing approach, involving the removal of pointing "contamination" from collimation data, are given in this paper.
© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A. Rakich, D. Thompson, O. P Kuhn, "Range-balancing the Large Binocular Telescope", Proc. SPIE 8128, Current Developments in Lens Design and Optical Engineering XII; and Advances in Thin Film Coatings VII, 812808 (8 September 2011); doi: 10.1117/12.893166; https://doi.org/10.1117/12.893166
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KEYWORDS
Telescopes

Mirrors

Collimation

Data modeling

Active optics

Temperature metrology

Interferometry

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