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


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  • Aperture: 203 mm (8")
  • Focal Ratio: f/8
  • Focal Length: 1625mm
  • Back Focus: 250mm

Product Details

  • 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. 

    Optical:This TPO Ritchey Chretien telescope has 8 inches (200mm) of aperture and a focal length of 1625mm. 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 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 & Maksutov-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!

  • specifications

    Aperture203 mm (8")
    Back Focus250mm
    Camera/Eyepiece Connection2" nosepiece
    Dawes Limit0.57 arcseconds
    Focal Length1624 mm
    Focal Ratiof/8
    Free ShippingYes
    Glass TypeQuartz
    Highest Magnification406x
    Limiting Magnitude15.3
    Optical DesignRitchey Chretien
    Secondary Obstruction85mm
    Tube Diameter230mm
    Tube Length559mm
    Tube Weight18.5 lbs
    Warranty2 Year Warranty
  • 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

Product Reviews

Customer Reviews
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    United States United States
    Fantastic Value!

    I'll be honest here. This was my first RC. I was very nervous about collimation because of all the talk I've heard about how difficult these can be to collimate. Truth be told, if you have the right tools, Collimating eyepeice and nice Laser collimator, it's really not hard to get good collimation on these scopes. My first light with this scope was a very good experience. Got a wonderful image of M81 at a focal length I'd only dreamed about before hand. If you're somewhat experience already with newtonians then go for it. This scope will not disappoint for imaging or viewing.

    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.

    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 ***** 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.