The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.

Abstract
1. Introduction
2. Optical Design
    2.1. Optical Layout of FCC
    2.2. Tolerance
    2.3. ND Filters
    2.4. Focus Analyzer
3. Mechanical Design of FCC
    3.1. Optical Bench Assembly
    3.2. Collimator
    3.3. Filter-Wheels Assembly
    3.4. Reimager
    3.5. Detector Module
4. Structural and Thermoelastic Analyses
    4.1. Analysis on the Lens Mount Bezel
    4.2. Thermoelastic Analysis on FCC
    4.3. Global Structural Analysis on FCC
5. Conclusions
Acknowledgments
References

• Jae Sok Oh(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Chan Park(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea) Corresponding Author
• Kang-Min Kim(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Heeyoung Oh(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• UeeJeong Jeong(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Moo-Young Chun(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Young Sam Yu(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Sungho Lee(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Jeong-Gyun Jang(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Bi-Ho Jang(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Sung-Joon Park(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Jihun Kim(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Yunjong Kim(Korea Astronomy and Space Science Institute, Daejeon, 34055, Republic of Korea)
• Andrew Szentgyorgyi(Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02140, USA)
• Stuart McMuldroch(Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02140, USA)
• William Podgorski(Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02140, USA)
• Ian Evan(Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02140, USA)
• Mark Mueller(Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02140, USA)
• Alan Uomoto(The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA)
• Tyson Hare(The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA)
• Jeffrey Crane(The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA)