About Ritchey-Chretien Telescopes…
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.
12" f/8 Ritchey-Chretien Truss Tube Astrograph Highlights…
Optical Highlights: This Third Planet Optics (TPO) Ritchey Chretien telescope has 12" (300mm) of aperture and a focal length of 2432mm. 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.
Carbon Fiber Truss Tube Design:
Lightweight yet strong carbon fiber truss tubes have low thermal expansion characteristics. Shifts in focus due to temperature changes are minimized because of this design. The trusses are also designed to flex equally, keeping the optics in collimation regardless of the position of the telescope.
Cooling Fans: The 12" Ritchey has three small cooling fans in the rear cell that help cool the inside of the tube down and bring it to ambient temperature so that you can start imaging sooner! The fans are powered by an external battery pack. This battery holder accepts 8-AA batteries (sold separately).
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 D Style Losmandy Dovetails Included Talk about versatility! Two Losmandy-style dovetails are attached to the truss tube support rings so that they ride at the top of the scope as well as at the bottom.
TPO 3" Focuser A 3" dual-speed linear-bearing Crayford-style focuser rounds out this package. The ridged focusing knobs are easy to turn, even with gloves on, and the 10:1 microfocusing dial allows for very small changes, or tweaks, in focus. It takes ten turns of the microfocusing knob to equal just one turn of the larger knob. There is also a little knob on the bottom of the focuser that controls the tension, so that you can make adjustments depending on the weight or distribution of your load. The 3" opening steps down to a 2" compression ring adapter, and you will receive 1.25" compression ring adapter so that you can make use of all your eyepieces. Two 25mm and one 50mm extension tube is also included to help you match the back-focus requirements of your imaging equipment. This is one nice focuser, and due to its steel drive rail and other upgrades, you will find that it suffers from very little flexure, even under heavier imaging payloads.
- Additional Information
SKU OS-12RC-TT Manufacturer TPO Telescope Series TPO Ritchey-Chretien Optical Design Ritchey-Chretien Mount Type None - Optical Tube Only Warranty 2 Year Warranty Telescope Aperture 12" Telescope Focal Length 2432mm Telescope Focal Ratio f/8 Optical Tube Weight 52.9 lb. Optical Coatings 99% Dielectric Tube Color or Finish Carbon Fiber Look Diagonal Included? No - Sold Separately Finder Included None OTA Mount Type Losmandy-Style Dovetail
- Included Items
- TPO 12" f/8 Ritchey-Chretien Truss Tube OTA
- 3" Crayford Focuser
- Two Losmandy D Style Dovetails
- Questions & Answers
Product QuestionsHi: Does your 12" truss tube come with a a cover to protect the primary? Can one use it for visual observing and how is it visually? Can you see any secondary reflections? Also, is a focal reducer to f5 or so available? Thanks so much, LarryQuestion by: Morstar on Aug 19, 2014 3:00:51 AMThe 12" Truss RC does not currently include a primary mirror cover.
You can use the scope visually, but the large secondary mirror that helps imaging illumination will lower visual contrast compared to similar aperture scopes. The optics are very sharp but must be accurately collimated for best performance.
The scope is baffled to prevent most off axis reflections, but a shroud may help with this.
People have had good luck with the Astro-Physics CCDT67 focal reducer, which can lower the focal length to around f/5.4-6.0 depending on spacing, but this only works for an imaging circle around 25-29mm. Lunt Engineering is working on an f/6 reducer for larger sensors, but it has not been released yet as of mid-August 2014.Answer by: Chris (Admin) on Aug 19, 2014 11:09:21 AMWhat is the % obstruction by the secondary mirror (diameter or area should be specified in answer)? Thanks.What provision do the TPO 12" and 14" f/8 Ritchey-Chretien Truss Tube OTA have for finder scope (I.e., I plan to utilize one of the Losmandy dovetails to mount the telescope and the other for guide scope)? I think I see a finder scope bracket in one of the photos, but no detail is provided on finder scope mount compatibility?Do you have the image circle in mm ? Also is there a focal reducer available for it and what is the image circle in mm with that focal reducer.
Thank youQuestion by: Benoit Gagnon on Aug 23, 2015 3:13:00 PMWithout flattener, the image circle is 30-35mm.
You can use the AP-CCDT67 focal reducer which will give you approximately a 26mm. Also, Teleskop Service does make a corrector that will increase the image circle to 45mm (but it's not a reducer).Answer by: Jonathan Cheek (Admin) on Aug 23, 2015 4:50:00 PM
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