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.
Carbon Fiber Optical Tube: Besides being very high tech and impressive-looking, carbon fiber is light-weight, strong, and has a lower coefficient of expansion than aluminum. That means your OTA will be tough and not weigh more than it has to, but also that your focus won't tend to shift as temperatures change throughout the night.
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! A Losmandy-style dovetail is attached to the bottom of the OTA, and a Vixen-style dovetail rail is attached to the top for quick and easy attachment to 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!
Bobs Knobs- Limited Time Offer!
- Additional Information
SKU OS-8RC-CF 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 1625mm Telescope Focal Ratio f/8 Length of Optical Tube 21.8" Optical Tube Weight 16.4 lbs. Optical Coatings 99% Dielectric Tube Color or Finish Carbon Fiber Limiting Stellar Magnitude 14.2 Highest Useful Magnification 300x Diagonal Included? No - Sold Separately Finder Included None OTA Mount Type Losmandy-Style Dovetail
- Included Items
- TPO 8" f/8 RC Carbon Fiber OTA
- (2) M90 X 25mm Spacers
- M90 X 50mm Spacer
- Losmandy-style Dovetail
- Vixen-style Dovetail
- TPO 2" Two Speed Crayford Focuser w/ 1.25" Adapter
- Vixen Finder Shoe
- Dust Caps
- Questions & Answers
Product QuestionsThe specifications for the carbon fiber version of this scope has the same weight as the steel scope. Is this possible? If so, why would you choose the much more expensive carbon fiber version of the scope?Question by: sinsonte on Oct 6, 2014 4:09:46 PMThe two scopes do have nearly identical weights. The reason to choose the carbon tube is the greater thermal stability (much lower coefficient of expansion due to temperature) compared to steel, making image focus more stable during long exposures.Answer by: Chris (Admin) on Oct 7, 2014 11:38:26 AMIs there enough back focus to use an off-axis guider. If so, is one of the ultra thin ones required?1. I assume this is an AstroTech telescope? 2. Is a focal reducer/field flattener available? 3.Can the Orion electric focuser motor be fitted to the focuser? If not do you have an equivalent? 4. I assume the Losmandy dove tail is the 3 inch D dove tail?Question by: Bobbo on Jul 29, 2014 2:51:18 AM1. The TPO scopes are actually manufactured by Guan Sheng Optical. AstroTech purchases their scopes from the same manufacturer so they are effectively the same scope.
2. There is a very good field flattener made by Teleskop-Service with a 45mm image circle, but it is not a reducer. Lunt Engineering is planning on releasing a reducer-flattener soon, but it will be rather pricy as it is for 35mm format coverage. The simple TPO/GSO reducer will work for CCDs up to 15mm diagonal, but it is not a corrector.
3. We would have to check with Orion, but I would assume not. The shaft diameters would need to be identical between the Orion and TPO focusers. I know both Robofocus and Rigel have motors that work on this focuser.
4. Yes, the dovetail on the bottom is a 3" D-series dovetail, while the dovetail on top is a narrower Vixen V-series.Answer by: Chris (Admin) on Jul 30, 2014 7:24:23 AM
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