Ritchey-Chrétien (RC) Telescope collimation

• Optically align 2 hyperbolic mirrors and a focuser
• Set correct mirror distance

• Adjusting one of the mirrors or the focuser affects the alignment of the others
• Mechanical axis is rarely also the optical axis
• Most tools wrongly assume that the optical axis is the same as the mechanical axis
• Mirror distance is critically important
• Some models have (had?) a focuser attached to the primary mirror assembly without collimation capabilities.
• Central rings in the mirrors are not always at the optical center
• Most models have no adjustment options to recenter the mirrors.

Collimation using stars at night

• Deepsky Instruments method http://www.deepskyinstruments.com/truerc/docs/DSI_Collimation_Procedure_Ver_1.0.pdf
• Mirror spacing by measuring focal length via platesolving.
• SkyWave-Collimator, AI based wavefront sensing https://www.innovationsforesight.com/
• ASTAP image inspection for the primary (after having aligned the focuser and the secondary with a laser during daylight).
• Tri-Bahtinov-Mask. This should be usable for the primary (after having aligned the focuser and the secondary with a laser during daylight)
• Mirror spacing with a star
• scrutinize a star at high mag and adjust the PM/SM despace until the spherical aberration goes away by Tom Dey

Collimation during daylight

• Hall of Mirrors method, symmetrical bisected crescent moons https://www.cloudynights.com/topic/782014-rc-collimation-with-no-laser-or-stars/page-6#entry11276346
  • Not really usable with a 30cm model, the secondary size leaves only a few reflections to work with.
• Kitchen table collimation of a Cassegrain-type reflector by Russ Slater https://britastro.org/2018/kitchen-table-collimation-of-a-cassegrain-type-reflector
• RC collimation with no laser or stars https://www.cloudynights.com/topic/782014-rc-collimation-with-no-laser-or-stars/
• Paper or plastic disk with a central hole for the primary
• https://www.cloudynights.com/topic/782014-rc-collimation-with-no-laser-or-stars/?p=11260952
• Collimating_GSO_Ritchey_Chretien_with_a_plastic_disc_V2-for-old-RC6-RC8-designs.pdf by David Davies
• Cheshire eyepiece for the secondary
• Takahashi TKA00443 collimator
• Takahashi TCEE0100 collimator
• http://www.alluna-optics.com/Alluna-Blog/113-collimation-RC-telescope.html
• HOTECH Advanced CT Laser Collimator http://www.hotechusa.com/category-s/23.htm
(aka Hotech ACT)
• Manual V8, 7 pages https://www.hotechusa.com/v/vspfiles/assets/images/ACT%20Laser%20Collimator%20Manual%20V8.pdf
• Collimation video https://www.youtube.com/watch?v=wgDBktsX3fI&list=PL80AADE80AB76336D
• https://www.cloudynights.com/topic/509460-daytime-collimation-of-a-cassegrain-scoperc/
• https://www.cloudynights.com/topic/714340-collimation-experience-with-hotech-act-and-ritchey-chr%C3%A9tien/#entry10288647 use the ACT on an RC
• http://jropics.com/collimation.html use the ACT (and SCA and HG) on an RC
• Howie Glatter with the Concentric Circle attachment
• https://stargazerslounge.com/topic/349932-help-please-collimating-an-rc-with-a-howie-glatter/
• http://stevesastro.blogspot.com/2013/05/collimating-my-gso-rc8-telescope.html
• Mirror spacing with a Ronchi
• Ronchi-testing-the-focal-length.pdf by David Davies
• TSRCKOLLI, https://www.teleskop-express.de/shop/product_info.php/language/en/info/p11188_TS-Optics-2--LED-Collimator-for-RC-Telescopes-and-all-other-Types-of-Telescopes.html
• Bench Collimating a GSO RC8 https://www.ancientphotonsastro.com/post/bench-collimating-a-gso-rc8

Further reading

• http://interferometer-tests.blogspot.com/2013/06/2542000-10-ritchey-chretien-gso.html by Tommy Nawratil from www.teleskop-austria.at
• https://www.cloudynights.com/topic/703752-gso-16-inch-rc-collimate-with-an-autocollimator/?p=10961496 by Dr. Gaston Baudat from Innovations Foresight.
• laser collimator and test tilt by rotating
• laser collimator for the secondary mirror
• primary mirror tilt with a Takahashi collimation scope
• defocused star near zenith
• plate solving to measure mirror distance is a coarse predictor due to few percents of focal length differences between otherwise identical scopes
• offset of the secondary central obstruction with photo examples
• Shack-Hartmann (SH) wavefront analyzer
• intro to their ai based wave front sensing and collimation software
• https://www.cloudynights.com/topic/646374-not-another-gso-rc-collimation-thread/
• https://www.cloudynights.com/topic/514199-rcs-a-scope-for-masochists/
• http://www.hnsky.org/RC_collimation.htm
• https://www.cloudynights.com/topic/760224-rc-distortions/
• https://www.cloudynights.com/topic/657216-rc8-collimating-frustration/ by Robin Brown. Instruction set pdf: RC8-Collimating-Frustration-revision-1.4.pdf
• https://www.cloudynights.com/topic/693000-what-happened-to-my-collimation-on-a-12-inch-ritchey-chretien/
• https://www.cloudynights.com/topic/711668-adjusting-focal-length-of-16-inch-ritchey-chretien-scope/
• Cedric Raguenaud's Idiot-proof guide to Ritchey Chretien collimation RC-collimation-by-Cedric.pdf from https://raguenaud.space/2021/03/collimation-du-rc-partie-3/
• https://www.astroforum.nl/threads/collimeren-ritchey-chretien-artificial-star-of-collimator.1471289/
• https://deepspaceplace.com/gso8rccollimate.php
• https://www.starry-night.nl/stap-voor-stap-collimatie-van-een-rc/ by InFINNityDeck
• https://stargazerslounge.com/topic/177312-altair-10-rc/
• Third-order astigmatism of a Ritchey-Chrétien telescope.https://spie.org/news/1763-when-excellent-on-axis-performance-is-not-good-enough?SSO=1
• SkyWave-Collimator by Dr. Gaston Baudat - Using AI for Telescope Collimation https://www.youtube.com/watch?v=u--0h5R7jBU
• A solution for focusers attached to the primary mirror assembly without collimation capabilities: https://www.cloudynights.com/topic/827768-finally-made-an-rc-collimation-adapter/
• page 88 and Appendix F in "Star Testing Astronomical Telescopes." by Harold Suiter.
• pages 395 - 419 in the "The Astrophotography Manual, 2nd ed." by Chris Woodhouse.
  Topics discussed :
  • Cheshire
  • Takahashi collimating scope
  • Howie Glatter laser with concentric rings attachment
  • Hotech Advanced CT laser
  • Hall of mirrors
  • Theodolite
  • Artificial star
  • 9-ball tester
  • Classic star testing
  • GoldAstro collimation mask. (A tri-bahtinov mask.)
  • Mirror separation

Last page update : 2023-04-08T15:05Z -- Hans Lambermont