Ritchey-Chrétien astrographs

More Information  · Recommended Accessories  · Related Documents  · Images of Some Features Price $2,995.00 Focal Length 2000mm Focal Ratio f/8 Resolution 0.46 arc seconds Aperture 10" Weight 33.6 lbs. Warranty 2 years

   Astro-Tech Ritchey-Chrétien optics

This Astro-Tech AT10RCF Ritchey-Chrétien astrograph has: • 10" f/8 true Ritchey-Chrétien hyperbolic mirror optical design • low thermal expansion quartz primary and secondary mirrors • 99% reflectivity non-tarnishing multi-layer dielectric mirror coatings • center spotted secondary mirror • low thermal expansion carbon fiber optical tube • nine contrast-enhancing main tube knife edge light baffles • shipped without focuser to allow you to add the premium focuser of your choice • 1" and 2" focuser extension rings to fine-tune the back focus of your optional focuser • three built-in cooling fans in rear cell • two Losmandy-style “D-plate" dovetail rails • mounting bracket for optional finder • two-year warranty

    The 10" Astro-Tech AT10RCF is the first truly affordable carbon fiber large aperture true Ritchey-Chrétien astrograph available from a U. S. company. Imitators will no doubt copy Astro-Tech’s years of hard development work, but why settle for a copy when you can get the original? Sky & Telescope agrees, as they named the Astro-Tech 8" and 10" Astro-Tech Ritchey-Chrétien astrographs Sky & Telescope Hot Products for 2010. (Incidentally, the original Astro-Tech 6" R-C was named a Sky & Telescope Hot product for 2009 and the new 12" AT12RC has been named a Hot Product for 2011.)

    The surprisingly affordable Astro-Tech AT10RCF (and its even more affordable metal tube brother, the AT10RC) joins two other Astro-Tech Ritchey-Chrétien firsts. One is the AT8RC, a Sky & Telescope Hot Product for 2010 – the first 8" true Ritchey-Chrétien astrograph available from a U. S. company and the first and still the only affordable U. S. 8" R-C with Astro-Tech-designed premium features like quartz mirrors, dielectric mirror coatings, two dovetail mounting rails, and more. The other is the AT6RC – a highly affordable R-C astrograph for webcam, DSI, and DSLR imaging that was conceived and developed by, and first brought to market by, Astro-Tech and named a Hot Product for 2009. Both the AT6RC and the AT8RC were highly praised in a four-page review in the December 2009 issue of Sky & Telescope magazine.

    And we are serious when we say the 10" aperture AT10RCF is “affordable." The premium feature carbon fiber Astro-Tech AT10RCF is priced thousands of dollars less than the formerly least-expensive phenolic tube 10" R-C. As Sky & Telescope pointed out in their Hot Product citation in the January 2010 Sky & Telescope, “Ritchey-Chrétien reflectors are highly regarded among today's elite astrophotographers, and premium instruments often carry price tags starting at about $1,000 per inch of aperture. So it's the best kind of "sticker shock" to see the prices for Astro-Tech's 8- and 10-inch f/8 Ritchey-Chrétiens, which pack features too numerous to list here. Our review of the 8-inch scope appears in last month's issue (December 2009), page 38, and our initial hands-on look at the 10-inch suggests that it will be equally exciting for deep sky astrophotographers." The magazine also pointed out that the 10" Astro-Tech RC cost “about one-fourth what similar instruments did just a couple of years ago."

    The Ritchey-Chrétien optical design is used in virtually every recent large mega-million dollar professional observatory telescope – including the Hubble Space Telescope. The Astro-Tech AT10RCF astrograph (a telescope designed specifically for astronomical imaging, rather than visual observing) makes the coma-free imaging of true Ritchey-Chrétien optics available to the DSLR and large format CCD astrophotographer at a price less than that of many large format CCD cameras and DSLR camera bodies. Featuring first-quality 99% reflectivity dielectric mirror coatings and premium low thermal expansion quartz mirrors, rather than aluminized Pyrex glass mirrors, this economical 10" Astro-Tech carbon fiber R-C makes you wonder just what competitive high-price R-Cs have that makes them cost so much more.

    Designed for exceptional imaging, the Astro-Tech AT10RCF provides the coma-free photographic field that large format CCD astrophotographers crave, but can’t get from conventional reflectors and Schmidt-Cassegrains. Likewise, as a pure two-mirror system, the AT10RCF has a wide spectral response and is totally free from the spurious color that affects the imaging of all but the most costly apochromatic refractors, and it does it with an 10" aperture that dwarfs the light gathering of most apo refractors.

    An example of the kind of imaging possible with the AT10RCF is Brian Kimball’s exceptional image of NGC2244 shown below in the “images of some features" section. This open cluster of young stars is nestled within the Rosette Nebula, and was recently formed from that nebula’s material. Brian’s AT10RCF image easily stands up to a side by side comparison with photos taken by professional observatories using much larger and more expensive telescopes, as well as to those taken with the most expensive amateur astrographs.

    If serious astrophotography is your goal, but the price of most true Ritchey-Chrétien optics has been keeping you from the optical design used by most modern professional observatories and the Hubble Space Telescope for their imaging, your wait is over. The 10" Sky & Telescope Hot Product for 2010 Astro-Tech AT10RCF astrograph can bring the world of professional DSLR/CCD deep space imaging to your backyard observatory at a truly affordable price.

Features of this Astro-Tech AT10RCF Astrograph . . .

• Optical design: True Ritchey-Chrétien Cassegrain-type two-mirror optics, with hyperbolic primary and secondary mirrors. For more details, click on the “optics" icon above. The 235mm available back focus allows for the use of long CCD equipment trains.

• Optical specifications: 10" aperture, 2000mm focal length, f/8 focal ratio.

• Hyperboloid primary mirror: Made of low thermal expansion quartz, rather than the Pyrex used by competitors. Ground and polished under precision computer control. Unlike catadioptric designs (SCTs, Maksutovs, etc.) that move the primary mirror fore and aft in the optical tube to focus (which can lead to image shift as the mirror position changes) the AT10RCF primary mirror is fixed to eliminate both a catadioptric’s image shift and the frequent primary mirror collimation requirements of a Newtonian reflector. Collimation is pre-set at the factory but can be adjusted, if needed, using three traditional push/pull locking adjustment screw sets.

• Hyperboloid secondary mirror: Made of low thermal expansion quartz, rather than the Pyrex used by competitors. Ground and polished under precision computer control. Mounted in a four-vane spider and fully collimatable using simple standard Cassegrain reflector collimating techniques. The secondary mirror is precisely center-spotted to make collimation easier. Unlike complicated R-C designs that use motors to move the secondary mirror fore and aft to focus, the AT10RCF secondary mirror is fixed and focusing is done externally.

      The December 2009 issue of Sky & Telescope said that the Astro-Tech R-C’s fixed primary and secondary mirrors “eliminate image shift, which has been the bane of Cassegrain scopes with moving-mirror focusing systems . . . It also keeps the effective focal length of the system constant, and the infinity focal point remains at a fixed point outside of the telescope, neither of which is the case with moving-mirror systems that change the separation between a Cassegrain’s primary and secondary mirrors."

• 99% reflectivity dielectric coated optics: Both primary and secondary mirrors have non-tarnishing state-of-the-art multi-layer dielectric mirror coatings. These have a full 99% reflectivity for the brightest possible images. This is higher than the unspecified (but typically 94-96%) reflectivity of the enhanced aluminum coatings used by competitors.

• Multiple internal light baffles: Computer optimized primary and secondary baffling. Nine contrast-enhancing glare-stop knife-edge baffles in the optical tube; multiple glare-stop microbaffles in the secondary mirror light shield; baffles in the primary mirror baffle tube, and baffles in the focuser drawtube, provide truly dark sky backgrounds during imaging.

• Carbon fiber optical tube: Made of a high strength woven carbon fiber-reinforced epoxy-coated composite with extremely low thermal expansion characteristics to reduce the possibility of temperature-related focus changes during an exposure that can occur with aluminum or rolled steel tube systems. Die-cast and machined aluminum front and rear cells. The carbon fiber tube is dent-proof and virtually indestructible. Carbon fiber composites are so strong that the new $200,000,000 Boeing 787 Dreamliner passenger jet will use a wing and fuselage made almost entirely out of carbon fiber.

      The December 2009 issue of Sky & Telescope said of the carbon fiber tube used in the 8" Astro-Tech RC, "the carbon-fiber tube did a good job of holding focus over the modest temperature changes occurring during my summer evenings. More telling, perhaps, was the scope’s tendency to remain accurately focused after several days of inactivity during which the temperature in my backyard observatory would cycle over a huge range."

• No focuser is supplied: Many astro-imagers already have a premium focuser being used on another scope that they would like to use for imaging, or they have a preference for one particular focuser manufacturer over another. Rather than pre-installing a focuser of our choosing, and to give you the most flexibility in choosing your own focuser for imaging, no focuser is supplied with the AT10RCF. This allows you to choose your own focuser, depending on your preferences. One possible choice might be the dual-speed 3" Feather Touch #3015 rack and pinion, with #M117 adapter (#3015/M117).

      The rear cell of the AT10RCF has a male 117m x 1mm pitch threaded port for attaching a focuser. The standard Feather Touch 3" diameter 1.5" travel focuser normally comes with a 109mm threaded collar for connecting to a scope. However, in its #3015 configuration (Feather Touch part #FTF3015B-A), it also requires a #M117x1 Feather Touch adapter to be used with the AT10RCF. The #3015 focuser (without 109mm collar) slips into this adapter and is held in place by three large brass Delrin-tipped retaining knobs. Only focusers with a maximum 1.5" drawtube travel, such as the Feather Touch #3015, are recommended for use with the Astro-Tech AT10RCF 10" Ritchey-Chrétien. For brands of focusers other than Feather Touch, such as MoonLite, contact the focuser manufacturer for an adapter to fit the 117mm x 1mm port on the rear of the scope.

      To fine-tune the back focus of the AT10RCF to the requirements of your camera and equipment train, three threaded extension rings (two 1" in length and one 2") are provided to install singly or in combination between the AT10RCF rear cell and the focuser of your choice. These provide a flex-free solid metal extension that changes the distance between the focuser and the rear cell. This lets you accommodate the varying back-focus requirements of DSLR-type camera imaging versus long equipment train CCD imaging. The two 6.4 ounce 1" extension rings and one 14.4 ounce 2" ring add 1.7 pounds to the weight of the scope when all rings are installed.

      Because of the 33.6 pound weight of the AT10RCF (without extension rings, but with a typical focuser), plus the weight of your ancillary camera equipment and any photoguide scope, installing the AT10RCF on a German equatorial mount with a 60 to 100 pound payload capacity is recommended. Such mounts include the 90 pound capacity Celestron CGE Pro and the Losmandy 60 pound capacity G11 or G11 go-to and 100 pound capacity Losmandy HGM Titan. Other suitable mounts are also available.

• Optional field flattener: For even more impressive coma-free imaging with the AT10RC, consider adding the Astro-Tech AT2FF field flattener. While not specifically designed to work with Ritchey-Chrétien astrographs, images taken with the field flattener by Astro-Tech R-C owners have shown that the Astro-Tech 2" field flattener works remarkably well with these advanced coma-free reflectors as well as with refractors. This modestly-priced imaging accessory essentially eliminates the residual field curvature inherent in all reflector telescope designs, so that the coma-free star images remain point-like all across the field. An optical analysis and ray tracing of the field flattener was done in ZEMAX and applied to the R-Cs by Roger Ceragioli, the noted optical designer who did the final optimization of the Astro-Tech Ritchey-Chrétien optics. Here is what he had to say about the #AT2FF, “My conclusion, which seems supported by what users are saying, is that you don't need any other field flattener. This one performs well over a 40mm image circle in all three small RCs (6", 8", and 10")."

• Cooling fans: To allow the AT10RCF to reach ambient temperatures more quickly for optimum imaging performance, there are three small low vibration/high CFM primary mirror cooling fans built into the rear cell. The high speed DC fans are powered by a standard equipment battery pack that plugs into a jack on the rear cell. The battery pack uses eight user-supplied AA batteries. An optional external DC power supply, such as a rechargeable 12VDC battery pack can also be used to power the fans.

• Two dovetail mounting rails: Two Losmandy-style “D-plate" dovetail rails are provided for installing the AT10RCF on an equatorial mount, as well as for mounting optional accessories (such as rings for a photoguide scope) on top. The 21" long dovetail rails run the length of the optical tube. One is mounted underneath the tube for installing the 33.6 pound AT10RCF directly on a suitable payload capacity Losmandy-style equatorial mount. The second dovetail rail is mounted 180° away from the first, on top of the tube. This can be used for installing a photoguide ring set, piggyback camera adapter, or any other accessory that attaches to a scope by means of Losmandy-style “D-plate" dovetail adapters. The undersides of the dovetails have been hollowed out to lighten their weight without compromising their strength, as can be seen in the side-view feature image below.

• Finderscope dovetail: A Vixen-style finderscope bracket dovetail base is installed on the upper left side of the optical tube's rear cell. It can easily be removed if not needed. It will accept Vixen-style finderscope brackets as well as red dot-type finders, such as the Astro-Tech #ATF.

• Other accessories: A snap-in dust cap is standard.

• Two year warranty: As an expression of the confidence Astronomy Technologies has in the quality of their products, the Astro-Tech AT10RCF is protected by a two-year limited warranty against flaws in materials and workmanship.