Astro Tech 10" f/8 Ritchey-Chretien Astrograph AT10RC

This Astro-Tech AT10RC Ritchey-Chretien astrograph features

• 10" f/8 true Ritchey-Chretien hyperbolic mirror optical design
• Low thermal expansion quartz primary and secondary mirrors
• 99% reflectivity non-tarnishing multi-layer dielectric mirror coatings
• Nine contrast-enhancing main tube knife edge light baffles
• Dual-speed 3" linear bearing Crayford focuser
• Three built-in cooling fans in rear cell
• 1.25" and 2" compression ring accessory holders
• 1" and 2" focuser extension rings to fine-tune the back focus
• Two Losmandy-style "D-plate" dovetail rails
• Mounting bracket for optional finder
• Two-year warranty

After several years of joint development with the manufacturer, Astro-Tech is proud to announce that the 10" f/8 AT10RC Ritchey-Chretien is now in production. The Astro-Tech AT10RC is the first truly affordable large aperture true Ritchey-Chretien 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 and and Telescope agrees, as they named the Astro-Tech AT10RC a Sky and and Telescope Hot Product for 2010, along with its smaller 8" brother, the Astro-Tech AT8RC. (Incidentally, the original Astro-Tech 6" R-C was named a Sky and and Telescope Hot product for 2009.)

The affordable Astro-Tech AT10RC joins two other Astro-Tech Ritchey-Chretien firsts. One is the AT8RC, also a Sky and and Telescope Hot Product for 2010 - the first 8" true Ritchey-Chretien 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 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 and and Telescope magazine.

And they are serious when they say the 10" aperture AT10RC is "affordable." The Astro-Tech AT10RC is priced nearly $4000 less than the formerly least-expensive 10" R-C. As Sky and and Telescope pointed out in their Hot Product citation in the January 2010 Sky and and Telescope, "Ritchey-Chrtien 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 /8 Ritchey-Chretiens, 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 AT10RC cost "about one-fourth what similar instruments did just a couple of years ago."

The Ritchey-Chretien optical design is used in virtually every recent large mega-million dollar professional observatory telescope - including the Hubble Space Telescope The Astro-Tech AT10RC astrograph (a telescope designed specifically for photographing comparatively wide areas of the sky) makes the coma-free imaging of true Ritchey-Chretien imaging optics available to the DSLR and large format CCD astrophotographer at a price less than that of many large format CCD cameras. Featuring first-quality 99% reflectivity dielectric mirror coatings and premium low thermal expansion quartz mirrors, this economical 10" Astro-Tech 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 AT10RC provides the wide 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 AT10RC 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.

If serious astrophotography is your goal, but the price of most true Ritchey-Chretien optics has been keeping you from the optical design most modern professional observatories and the Hubble Space Telescope use for their imaging, your wait is over. The 10" S and and T Hot Product for 2010 Astro-Tech AT10RC 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 AT10RC Astrograph

• Optical design: true Ritchey-Chretien Cassegrain-type two-mirror optics, with hyperbolic primary and secondary mirrors. The 300mm 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 AT10RC primary mirror is fixed to eliminate both a catadioptric's image shift and the frequent primary mirror collimation requirements of a Newtonian reflector.

• 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. Unlike complicated R-C designs that use motors to move the secondary mirror fore and aft to focus, the AT10RC secondary mirror is fixed and focusing is done externally. The December 2009 issue of Sky and and 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 reflectivity (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; and baffles in the primary mirror baffle tube to provide truly dark sky backgrounds during imaging.

• Dual-speed 3.3" linear bearing Crayford focuser: A newly-designed extra-sturdy "linear bearing" Crayford focuser is threaded onto the rear cell of the AT10RC. A locking collar allows the entire precision-made non-vignetting focuser to be rotated to the most convenient imaging angle and locked in place. There is 140mm (5.5") of back focus available with the focuser installed (235mm from the rear cell of the scope, without focuser, to the focal plane).

The focuser has dual-speed focusing. There are two coarse focusing knobs. The right knob also has a smaller concentric knob with a 10:1 reduction gear microfine focusing ratio. This provides exceptionally precise image control during critical imaging. All focus knobs are ribbed, so they are easy to operate, even while wearing gloves or mittens in cold weather. A lock knob underneath the focuser lets you adjust the tension on the drawtube to accommodate varying equipment loads. A large lock knob on top of the focuser lets you lock in your photographic focus.

The new linear bearing focuser has a polished stainless steel drive rail that runs the length of the underside of the drawtube. The focuser's stainless steel drive shaft presses on this drive rail to move the focuser, rather than having the hard steel drive shaft press directly on (and wear out) the softer aluminum drawtube as with conventional Crayford focusers. The steel drive rail rides in a self-lubricating track that extends almost the entire length of the focuser body. The drive rail and its attached drawtube are thereby supported over most of their length at all times, rather than by a conventional Crayford focuser's two sets of small contact area roller bearings. This system distributes the drive force evenly over the entire drawtube, without concentrating it on a few small contact points. The result is a very rigid drawtube with essentially zero flexure and no wear (much less flat spots or uneven wear) on the focuser drawtube.

To fine-tune the long 140mm back focus of the AT10RC 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 AT10RC rear cell and the focuser. 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 the 14.4 ounce 2" ring add 1.7 pounds to the weight of the scope when all rings are installed.

Because of the 34.4 pound weight of the AT10RC (36.1 pounds with all extension rings in place) , plus the weight of your ancillary camera equipment and any photoguide scope, installing the AT10RC on a German equatorial mount with a 60 to 100 pound payload capacity is recommended. One mount that includes a 90 pound capacity would be the Celestron CGE Pro. Other suitable mounts are also available.

• Focusing scale: The focuser's 50mm (1.97") travel drawtube has scales marked in both 1/16th inch and 1mm increments so you can note individual focuser positions for easy return to the approximate correct focus when switching between varying photographic equipment combinations.

• Cooling fans: To allow the AT10RC 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.

• 1.25" and 2" compression ring accessory holders: The 3.25" o.d. focuser drawtube ends in a stepdown to a 2" accessory holder that uses a non-marring soft brass compression ring to hold 2" imaging accessories in place. The compression ring won't scratch the barrel of your accessories as an ordinary thumbscrew can. Two thumbscrews are provided to lock the compression ring on your accessories. Also supplied is a 1.25" accessory holder that slips into the 2" compression ring holder to let you use 1.25" imaging accessories. Like the 2" accessory holder on the drawtube, the 1.25" adapter also uses a non-marring soft brass compression ring.

• Two dovetail mounting rails: Two Losmandy-style "D-plate" dovetail rails are provided for installing the AT10RC 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 34.4 pound AT10RC directly on a suitable payload capacity Losmandy-style equatorial mount. The second dovetail rail is mounted 180 degree 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. 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 AT10RC is protected by a two-year limited warranty against flaws in materials and workmanship.

Optical features of this Astrograph . . .

• Ritchey-Chretien optical design: This Astro-Tech astrograph is a true Ritchey-Chretien (RC) reflector optical system. Unlike a Maksutov-Cassegrain or Schmidt-Cassegrain catadioptric scope (that uses simple spherical mirrors and corrector lenses), or Newtonian reflectors (that use a coma-producing parabolic primary mirror), this Astro-Tech RC is a Cassegrain-type two-mirror optical system that uses a concave hyperbolic primary and a convex hyperbolic secondary mirror to form its images. These sophisticated and difficult-to-make mirrors combine to produce images at the Cassegrain focus at the rear of this Astro-Tech scope that are free from coma and spherical aberration, with a smaller spot size, over a much wider field than conventional Newtonians or catadioptrics. The images are likewise free from the chromatic aberration found in refractors and some catadioptrics. Because of this wide coma-free field, small spot size, and relatively fast focal ratio, the Ritchey-Chretien design is particularly well suited to wide field astrophotography, rather than visual observing. For imaging, the RC is the optical system of choice for most of the major professional observatory imaging telescopes built in the last half-century. For example, the Hubble Space Telescope, the twin 10-meter Keck telescopes in Hawaii, and the four 8.2 meter telescopes of the Very Large Telescope array in Chile are all Ritchey-Chretiens. For serious amateur astronomers and astrophotographers without NASA's optical budget, an Astro-Tech RC is likewise the imaging system of choice.

• Fully multicoated quartz and BK7 mirrors: The primary mirror of the 6" Astro-Tech is first-quality BK7 optical glass, while the 8" and larger Astro-Tech RCs use primary mirrors of low thermal expansion quartz for maximum focus stability during long exposure imaging sessions. Both 6" R-C mirrors are vacuum-coated with enhanced aluminum for high reflectivity and overcoated with a durable layer of silicon monoxide (quartz) for long life. The 8" and larger mirrors are dielectric coated for long life and reflectivity approaching 99%+.

• Computer designed and fabricated optics: To keep the cost of each Astro-Tech RC so reasonable when compared to competitive RC scopes, the computer-optimized Astro-Tech hyperboloid mirrors are automatically ground and finished to very high tolerances using custom-made computerized mirror grinding machines. This precision computer control guarantees an exact repeatability of figure from mirror to mirror that is difficult to achieve using more costly conventional hand figuring. After grinding and polishing, each mirror is individually tested using a Zygo interferometer to assure that it meets or exceeds its designed performance standards.

• Frill-free design: To further keep its cost reasonable, an Astro-Tech RC does away with most of the bells and whistles found on competitive scopes that add little to their performance (but much to their cost). For example, Astro-Tech front and rear cells are first die-cast, then CNC machine-finished, rather than completely CNC machined from raw stock at considerably greater expense but no significant improvement in performance as is the case with other RCs. Glare stops in the optical tube are a molded insert, rather than machined aluminum, resulting in a significant savings in cost at no appreciable difference in performance. The Astro-Tech scopes use an external manual dual-speed Crayford focuser, rather than the considerably more complicated and much more costly motorized movable secondary mirror system that other manufacturers use for focusing. The result of the Astro-Tech no-frills approach is genuine Ritchey-Chretien wide-field performance at a fraction the cost of other commercial RC systems. While the mechanical bells and whistles may be limited in an Astro-Tech RC, an Astro-Tech scope still has the high precision flat field/coma-free true Ritchey-Chretien optics that are the most important reason for buying an RC scope.

Mechanical features of this Telescope's Optical System . . .

• Fixed primary mirror with computer optimized primary and secondary baffling: Unlike traditional Cassegrain designs that move the primary mirror fore and aft along the central baffle tube in order to achieve focus (which can lead to image shift as the mirror position is adjusted) each Astro-Tech RC primary mirror is fixed. The Astro-Tech is focused externally by means of a dual-speed 2" Crayford-style focuser on the rear cell, thereby eliminating a Cassegrain's moving mirror image shift during focusing. Molded field stops are installed along the interior of the optical tube to effectively prevent stray off-axis light from reaching the image plane, resulting in improved contrast. In addition multiple glare-stop microbaffles on the inner surfaces of the primary mirror baffle tube and the secondary mirror light shield further prevent off-axis light from reaching the image plane, resulting in still further improved contrast.

• Collimatable secondary mirror: Since the primary mirror of an Astro-Tech RC is fixed in position, only the secondary mirror can (or needs to) be collimated. This makes it easy to keep the Astro-Tech RC optics aligned for peak performance. Collimation adjustments to the secondary mirror are made by adjusting the three collimating screws in the back of the secondary mirror holder.

• Cooling fan: The open tube RC design allows for fast cool-down of the primary and secondary mirrors. Built-in fans on the rear cell of the 10" and larger scopes increases the air-flow around the optics to achieve still quicker "cool down" times of the larger primary mirrors. The 6" and 8" scopes do not have primary mirror cooling fans, as their mirrors are small enough to cool down quickly without any external aid.