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

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  • Regular price $399.00
  • TPO 6" f/9 Ritchey-Chretien Steel Astrograph with TPO 2" Focuser

    • Sale
    • Regular price $399.00
    • ITEM #

    • Will not ship until



    Free Shipping
    • Aperture: 152mm (6 inch)
    • Focal Length: 1370mm
    • Focal Ratio: f/9
    • 2 Year Warranty
    • Highest Magnification: 300x

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

    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 inch f/9 Ritchey-Chretien Astrograph Highlights


    Optical Highlights: This Third Planet Optics (TPO) Ritchey Chretien telescope has 6 inch (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 inch Dual Speed Crayford Focuser You'll love the 2 inch 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 inch compression ring adapter is also included so you can use both 2 inch & 1.25 inch 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!

    TPO Product Number: 6RC

    Additional Information

    Aperture152 mm (6")
    Focal Length1370mm
    Focal Ratiof/9
    Focuser DesignCrayford
    Focuser Size2"
    Free ShippingYes
    Manual or Electronic FocusingManual
    Optical DesignRitchey Chretien
    Warranty2 Year Warranty

    Customer Reviews

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    Questions & Answers

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    • Do you stock a second rail for mounting a guide scope?

      We 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 &

    • The big central obstruction reduces the contrast in DSO astrophotography?

      Contrast 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 tha

    • This OTA delivery 100% illuminated and fixed field in full frame DSLR or only in APS-C?

      Due 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 correcte

    • What is the capacity of the focuser, in kg?

      The included focuser is fairly lightweight and will carry up to approximately 1.5-2 kg max weight, though we usually do not recommend more than 1.5 kg to prevent flexure of the drawtube.

    • Hello, what is the backfocus of this telescope?

      The official backfocus is 150mm behind the 2" focuser (pulled forward, no 1.25" adapter attached). As the focuser is about 80mm long at minimum, the backfocus from the M90 thread is ~230mm.

    • 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 obser

      Yes! You can use the 6" TPO RC for visual use as well as astrophotography.

    • F/9 is a high number, Is there any focal reducer for this scope?

      Focal 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 dia

    • What is the weight of the OTA?

      The weight of the 6" f/9 RC OTA is approximately 15 lbs.

    • Does this scope include everything an amateur needs to take pictures, or will I need to purchase anything extra?

      That 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 u

    • Would you know the size of the O-ring in this OTA by the primary mirror. Mine is completely deteriorated. Diameter and thickness?

      We measured the one in the demo 6" TPO RC on our showroom, and it appears to have an inner diameter of ~48mm and a thickness of 3mm.

    • Is this corrected for astigmatism and if not is there a corrector for this model

      Thanks for your question. At this time we are unaware of a corrector for astigmatism for this telescope model.

    • Can you recommend a heavy duty focuser to replace the stock focuser?

      For 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 o

    • 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?

      The TPO 6" RC uses a standard vixen finder shoe. Any finder that has a standard vixen finder base will be compatible with this telescope. Give us a call or email us and we will match the finder that best fits your needs.

    • There is another site that offers a 6" F9 RC scope that seems to have more or less identical specs to yours, except that it claims a maximum 300x power, while yours specs a maximum 180x power. Can you explain the discrepancy, please?

      Our website also has 300x magnification for the TPO 6" f/9 RC Astrograph.