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
SKU OS-6RC 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 http://www.optcorp.com/te-rfl-4087-0-8x-reducer-tv102.html. 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
- 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 QuestionsQuestion by: Andres on Sep 3, 2015 3:27:00 AMFocal ratios of f/8 to f/9 are common with RC telescopes, and even research grade telescopes in the 20-60" range (0.5-1.5 meters) are usually ~f/8. TPO does make a 0.75x focal reducer (f/6.75), but it only works with sensors less than 15mm across the diagonal (a typical APS-C DSLR is 28-30mm across, so this would cover only the center 50%). A better recommendation is the Astro-Physics CCDT67, which can reduce the scope to f/6 to f/7 depending on spacing with a 28-33mm image circle). http://www.optcorp.com/astro-physics-ccd-telecompressor-for-f9-f18-telescopes.html.Answer by: Chris Hendren (Admin) on Sep 3, 2015 10:38:00 AMQuestion by: paulchess10 on Sep 1, 2014 10:50:14 PMContrast in astrophotography is less important than even illumination and a large, well-corrected field. Unlike in visual astronomy, you can add contrast back in with Photoshop later with astrophotography. It is better to have an obstruction too large than too small, as too small literally loses photons of light at the edge of the field.Answer by: Chris (Admin) on Sep 2, 2014 6:20:13 AMQuestion by: paulchess10 on Sep 2, 2014 7:52:00 AMDue to a customer pointing out a mistake with the previous answer, I am revising it here.
The illuminated image circle is 40mm, however it is not 100% illuminated out to the edge of this field. There is still natural light fall-off that must be corrected via flats. The corrected image circle is ~28mm without a flattener and ~40-45mm with a Telescop-Service RCKorrektor flattener, but this does not have a major effect on the light fall-off even though it does correct for field curvature.Answer by: Chris Hendren (Admin) on Jul 29, 2015 5:09:00 PMWould 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?Question by: Joe S. on Jun 30, 2016 3:29:00 PMThat depends greatly on your definition of "everything", but I would argue that at the least you would need a collimating tool (cheshire or laser with holographic attachment) and potentially a motor for the focuser. For heavier systems, you may need to upgrade the focuser, and flatteners and reducers are available depending on your camera system. Lastly, you will need a sturdy mount that can track and guide accurately at ~1400mm focal length to get the most out of this scope and an OAG/guiding setup.
Any scope can be upgraded depending on the user's tastes, and so very few scopes could be said to come with everything a user could need or desire right out of the box. If you have a specific setup in mind, please contact us and we will assist you in getting you any parts necessary for your needs.Answer by: Chris Hendren on Jun 30, 2016 3:39:00 PMQuestion by: John Massey on Feb 26, 2017 4:36:00 PMFor a manual focuser, the FTF2015 Feathertouch 2" focuser is an excellent option (SI-FTF2015BCR). IF you want a fully computerized focuser, consider the Optec TCFS-i focuser (OP-17668). Both focusers will require adapters to connect to the 90mm thread on the back of the 6" RC. The Starlight focuser can lift 5-8 lbs and the Optec can lift 10 lbs, so either should handle any camera syste you want to use. Please contact me by e-mail at firstname.lastname@example.org if you have questions.Answer by: Chris Hendren (Admin) on Mar 8, 2017 12:16:00 PMQuestion by: Blaine on Jun 1, 2014 6:43:09 PMWe are currently in the process of talking to the manufacture of this telescope about a dovetail plate for the top of the OTA so that accessories can be mounted on the top.
For the time being, the best way to get a system that has dovetails on the top & bottom of this telescope would be to get a set of Parallax rings that are custom sized at the time of order to this tube (Which can be ordered from us) & to get to Vixen or Losmandy (Depending on what kind of mount you have) style universal dovetail plates to mount onto the top & bottom of those rings.Answer by: Roderick (Admin) on Jun 2, 2014 1:05:49 PMGiven 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.
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