TPO 6" f/9 Ritchey-Chretien Steel Astrograph with TPO 2" Focuser

More Views

TPO 6" f/9 Ritchey-Chretien Steel Astrograph with TPO 2" Focuser
Item # OS-6RC

* Required Fields

  • Are you looking for an astrograph that doesn't break the bank? This Ritchey-Chretien, brought to you by TPO, is a true RC, with optics that produce flat, sharp images with virtually no false color or coma.
  • This 6" f/9 Ritchey-Chretien Astrograph OTA is a great choice for imaging with smaller sensors, including DSLR's.
  • Sometimes being baffled is a good thing! This Ritchey-Chretien telescope has 8 computer-optimized light baffles in the tube, the primary mirror tube has four internal baffles, and an internal glare thread baffle is part of the secondary mirror light shield.
  • A 2" 1:10 linear bearing Crayford focuser is included with this package. Focusing is super smooth, and the dual speed knobs allow you to make minute changes to focus as well as larger focus movement.
  • For terms and conditions please examine the TPO Warranty page here.



TPO 6" f/9 Ritchey-Chretien Astrograph OTA…


In 1910, American optician & astronomer George Willis Ritchey & French astronomer Henri Chretien designed a specialized Cassegrain that would later become the telescope of choice for many observatories and professionals around the world. The Ritchey-Chretien astrograph has many benefits that make this design appealing to anyone who is serious about astro-photography or imaging. Here are a few of those benefits:


    • Good-bye Coma: An RC has virtually no coma (stars look like little comets around the edges of the field), which means there will be greater image quality across a wider field of view.


    • No Chromatic Aberration: Because a Ritchey-Chretien does not use lenses or corrector plates, the design does not suffer from chromatic aberrations, or false color. If you've ever looked through an achromatic refractor (non-APO), you will have seen chromatic aberration.


    • No Spherical Aberration: The use of hyperbolic mirrors for both the primary and secondary removes the problem of spherical aberration from this optical system, an optical effect caused when light rays do not all come to focus at the same point, resulting in an image that is not in perfect focus.




6" f/9 Ritchey-Chretien Astrograph Highlights…


Optical Highlights: This Third Planet Optics (TPO) Ritchey Chretien telescope has 6" (152mm) of aperture and a focal length of 1370mm. The concave hyperbolic primary and convex hyperbolic secondary are made from a highly uniform BK7 glass blank, and finished with a scratch-resistant highly reflective dielectric coating for great contrast. The primary mirror is fixed in place in a metal mirror cell, and the secondary resides in a metal housing that can be collimated.

Multiple Knife-Edge Baffle System: The computer designed and optimized baffle system in the TPO Ritchey-Chretien works wonders at keeping stray light at bay. Inside the tube are eight light baffles, and the primary and secondary mirrors are baffled as well.

2" Dual Speed Crayford Focuser You'll love the 2" 1:10 Dual Speed Crayford focuser that comes standard on this RC. The dual knobs allow you choose the speed with which you focus. One turn of the larger knob equals ten turns of the smaller knob, so minute adjustments…when you are "almost there"…are easy to do with this high quality focuser. A 1.25" compression ring adapter is also included so you can use both 2" & 1.25" eyepieces. Two spacers are included as well, which allows you to adjust the focus position for different cameras with various back focus requirements.

A Fixed Primary Eliminates Image Shift Schmidt-Cassegrain & Mak-Cassegrain telescopes achieve focus by moving the primary mirror back and forth inside the optical tube assembly, and this movement can cause image shift. While manufacturers have done a pretty good job of minimizing image shift on their telescopes, a moveable mirror makes it almost impossible to eliminate it completely. The Ritchey-Chretien has a primary that is fixed in place, removing the possibility of image shift and also the job of collimating the primary.

Vixen-Style Dovetail Rail & Finderscope Base Included A full length Vixen-style dovetail rail is attached to the TPO Ritchey-Chretien optical tube assembly for quick and easy attachment to a Vixen-style mount. The rail can be removed if you wish to use mounting rings (sold separately) instead. While a finderscope is not included, the OTA comes standard with a finderscope base that will accept Vixen-style brackets (if you want an optical finder) or most red dot finders.

Long Back Focus of 150mm from the focuser or 230mm from the rear thread allows you to mount lots of imaging gear!

Additional Information

Additional Information

Manufacturer TPO
Telescope Series TPO Ritchey-Chretien
Optical Design Ritchey-Chretien
Mount Type None - Optical Tube Only
Warranty 2 Year Warranty
Telescope Aperture 6"
Telescope Focal Length 1370mm
Telescope Focal Ratio f/9
Length of Optical Tube 19.1"
Optical Tube Weight 12.3 lb.
Optical Coatings Aluminum
Tube Color or Finish Gloss White
Limiting Stellar Magnitude 13.6
Highest Useful Magnification 300x
Diagonal Included? No - Sold Separately
Finder Included None
OTA Mount Type Vixen-Style Dovetail

Customer Reviews 1 item(s)

Great Scope with the OPT Brand on it.
I received this sweet scope about a week ago and after the clouds cleared I had a chance to check it out. Right out of the box the collimation was perfect. I did get it to come to focus with an 30mm eyepiece with all 3 (4" total) of the extension rings in place and the diffraction rings were perfect and a few camera shots confirmed this. Next I used the 2" spacer ring to bring my Canon T3i to perfect focus and with the 1" ring I was able to get to focus with my Tele-Vue .8 FF/FR Using the FR/FF brings the scope down to an F/7.2 with a FOV of 45.5 x 68.3 arc min. with my camera. Overall I'm very please and the OPT scope comes with a 2 year warranty and 3 extension rings, this is better than the other 6"RC offered. It's a great value and backed up by OPT. Larry was a huge help and made it all come together and shipped it to North Carolina with out any hassle. This level of service is the main reason I am a repeat customer. Thanks Guys.

1= Houston, We Have a Problem & 5= It's Out of This World
Review by Robert / (Posted on 5/11/2013)
Included Items

Included Items

  • 6" Ritchey-Chretien Astrograph OTA
  • (2) M90 x 25mm Spacers
  • M90 X 50mm Spacer
  • Vixen Dovetail
  • 2" Two Speed Crayford Focuser w/1.25" Adapter
  • Vixen Finder Shoe
  • Dust Caps
Questions & Answers

Product Questions

The big central obstruction reduces the contrast in DSO astrophotography?
Is this corrected for astigmatism and if not is there a corrector for this model
F/9 is a high number, Is there any focal reducer for this scope?
Would you know the size of the O-ring in this OTA by the primary mirror. Mine is completely deteriorated. Diameter and thickness?
Does this scope include everything an amateur needs to take pictures, or will I need to purchase anything extra?
This OTA delivery 100% illuminated and fixed field in full frame DSLR or only in APS-C?
Hello, what is the backfocus of this telescope?
Can you recommend a heavy duty focuser to replace the stock focuser?
What is the capacity of the focuser, in kg?
Is there a finder scope with a mounting base that will fit the stock mounted finder scope mount or do I need to find a mount to fit other finder scopes?
Do you stock a second rail for mounting a guide scope?
What is the weight of the OTA?
Given the nature of this specialized scope, of coarse it is intended as an astrograph but how well would the scope function as a visual observation platform? I am new to space photography and visual astronomy with a telescope although I do binocular observation. Thank You for any help you might be able to share, Robert L.
Support / Downloads
Related Blog Posts