TPO 8" f/8 Ritchey-Chretien Steel Astrograph with TPO 2" Focuser

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TPO 8" f/8 Ritchey-Chretien Steel Astrograph with TPO 2" Focuser
Item # OS-8RC-M
  • At just 15 lbs., the TPO 8" f/8 Ritchey-Chretien Steel Tube Astrograph is portable enough to take on the road or to use in your own backyard.
  • Completely devoid of chromatic aberration, coma, and image shift.
  • Computer-optimized multiple knife-edge baffle system built into the TPO 8" f/8 RC Steel Astrograph does a magnificent job of suppressing stray light.
  • Concave primary and convex secondary hyperbolic mirrors are made of quartz and have 99% dielectric coatings for protected, highly reflective surfaces.
  • The TPO 8" f/8 RC Steel Astrograph comes with a 2" dual speed 360 degree rotatable Crayford focuser.
  • The OTA on this 8" f/8 model is made of rolled steel and painted white. It is also available in a carbon fiber version, which is shown in the image to the left.



Third Planet Optics (TPO) 8" f/8 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.



8" f/8 Ritchey-Chretien Astrograph Highlights…


Optical Highlights: This TPO Ritchey Chretien telescope has 8" (200mm) of aperture and a focal length of 1600mm. The concave hyperbolic primary and convex hyperbolic secondary are made from low expansion quartz, and finished with a scratch-resistant highly reflective 99% 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 ten 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.

Two Dovetails & Finderscope Base Included Talk about versatility! One Vixen-style dovetail is attached to the bottom of the OTA, while another Vixen-style dovetail rail is attached to the top for quick and easy attachment a variety of mounts. The rails 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 250mm allows you to mount lots of imaging gear!

Please Note: The image shows the carbon fiber version of this telescope. The rolled steel version is white with black metal trim. All other accessories are the same.

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 8"
Telescope Focal Length 1600mm
Telescope Focal Ratio f/8
Length of Optical Tube 21.8"
Optical Tube Weight 15.8 lb.
Optical Coatings 99% Dielectric
Tube Color or Finish Gloss White
Limiting Stellar Magnitude 14
Highest Useful Magnification 300x
Diagonal Included? No - Sold Separately
Finder Included None
OTA Mount Type Vixen-Style Dovetail

Customer Reviews 2 item(s)

Good scope hard to collimate
I have purchased one of the first units of this scope imported by OPT, but it is a proven design that has been sold under various brand names for a while now. This telescope works very well, but collimating it is difficult. Sooner or later your primary will need adjustment and the fun begins from there (if you call spending hours collimating a scope fun). Once you understand how it is done, it gets easier and easier, but it's not as simple as an SCT to collimate.

On the other hand, the scope is faster than a typical SCT, it cools down faster due to the open tube design and works pretty much as advertised. People complain about the focuser being attached to the primary mirror causing the primary to tilt and loose collimation. I have not experienced this with the 8" version, maybe it is an issue with the larger versions. However, you still need to buy a tilt plate so you can adjust focuser tilt. I have had to significantly tilt my focuser to reach good collimation.

The scope has 2 miles of back focus, so you can install a good focuser, a rotator, a filter wheel and a coffee machine.

There is also no reducer specifically designed for this scope and most of the reducers people use have one form of compromise or another when used with this scope.

Is it perfect? No. Would I recommend it? Yes... very few scopes at this price point offer what this scope does. So unless you have 3 to 4 times the budget, it is hard to get a better scope.
1= Houston, We Have a Problem & 5= It's Out of This World
Review by Hilmi / (Posted on 5/13/2015)
The TPO 8" RC telescope is a great buy.
The TPO 8" RC telescope is a great buy. There are a few differences on the included items for the better. It states two vixen rails but bottom rail is a losmandy. Since I have a G-11 this is great. Also it came with three screw on back focus adapters to deal with the larger back focus this scope has. You just unscrew the focuser from scope and insert how ever many adapters you need to get focuser in right range. No slope in optical path that way. I did an initial out of focus star test and it was not very far off from perfect. I cant wait for the next new moon to come to due some imaging with it. If you are looking forward to buying a RC telescope this is a good scope to start with and while they have there 15% discount you cant go wrong.
1= Houston, We Have a Problem & 5= It's Out of This World
Review by jeff / (Posted on 9/24/2013)
Included Items

Included Items

  • TPO 8" f/8 RC Steel Tube OTA
  • 2" Dual-Speed Crayford Focuser
  • (2) "V" Dovetails
  • 2" and 1.25" Compression Rings
  • Finderscope Mounting Shoe
Questions & Answers

Product Questions

What is the maximum resolution in arc second of the TPO 6" and 8" ritchey chretian astrographs.
Does this Vixen dove tail work with the CGEM DX saddle?
Is this a good telescope for normal viewing as well as doing astrophotography?
Is an OAG required/needed for guiding with this scope? If so which one would be suggested when using a DSLR for imaging? Thanks
Does the 8" steel tube RC come with the focuser extension rings?
Hi; just need to know what 'scheduled delivery' means, and is there a price difference between carbon fiber tube and rolled steel tube, if so, what is it? Thanks, Jeff
I have concerns with the amount of weight the stock focuser can handle. Would an Atik 383 w/ EFW filter wheel, offaxis guider and Starshoot guide camera be to much for the unit to handle?
Does this scope come with two vixen style divetails, or one vixen and one losmandy? I am considering this scope for our observatory, and we already have a G-11. Thanks!
Is this image circle of this OTA able to fill a full frame sensor (36mmx24mm)
How would you clean the primary mirror? I've seem reports that it would never need cleaning bit suspect thats optimistic
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