EXOhSPEC collimator mechanical design

Adipthep Kawinkija, Christophe Buisset, Hugh Jones, Bill Martin, Ronny Errmann

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

2 Citations (Scopus)
86 Downloads (Pure)


The Exoplanet High-Resolution Spectrograph (EXOhSPEC) is a high-resolution spectrograph for the characterisation of exoplanets with the Thai National Telescope. The folded version of this instrument comprises one triplet lens to collimate the beam incident on the grating and to focus the beam reflected by the grating onto the camera. This collimator comprises three lenses L1, L2 and L3 of diameter varying between 50 mm and 60 mm. We specified the barrel to guarantee a maximum decenter of the lenses equal to 25 μm. The maximum error in the orientation of each single lens is specified to be lower than 0.03º. The proposed concept is based on a semi-kinematic mounting which is used to restrain these lenses with 6 and 30 N of preloads on the axial and lateral directions to ensure their stability. These preloads are applied to the lenses using the elastic pushing force of silicone elastomers and spring force from ball-plungers. We present the design of the collimator and the assembly method. Our Finite Element Analyses show that the maximum surface error induced by the preloads is lower than 60 nm Peak-To-Valley on each optical surface of L1, L2, and L3. We describe our manufacturing process using NARIT’s CNC machine and its validation using our Coordinate-Measuring Machine.
Original languageEnglish
Title of host publicationProc. SPIE 11116, Astronomical Optics
Subtitle of host publicationDesign, Manufacture, and Test of Space and Ground Systems II
EditorsTony B. Hull, Dae Wook Kim, Pascal Hallibert
ISBN (Electronic)9781510629257
Publication statusPublished - 9 Sept 2019
EventSPIE Optical Engineering + Applications - San Diego Convention Center, San Diego, United States
Duration: 11 Aug 201915 Aug 2019

Publication series

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


ConferenceSPIE Optical Engineering + Applications
Country/TerritoryUnited States
CitySan Diego
Internet address


  • Astronomy
  • Design
  • Opto-mechanics
  • Precision engineering
  • Spectroscopy


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