Developed by Astro-Tech to make large-format CCD imaging affordable for the amateur astronomer, the Astro-Tech AT10RCF, a Sky & Telescope Hot Product for 2010, is priced thousands of dollars less than the formerly least-expensive 10 R-C. The Astro-Tech AT10RCF is the first truly affordable large aperture true Ritchey-Chretien astrograph available from a U. S. company. Even better, despite its low price, the Astro-Tech-developed AT10RCF has many of the same premium features as the much higher-priced competitive RCs (and some they don't have) like quartz mirrors, dielectric mirror coatings, carbon fiber body, Feather Touch rack-and-pinion focuser, and more.
This Astro-Tech AT10RCF Ritchey-Chretien astrograph has:
- 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
- center spotted secondary mirror
- low thermal expansion carbon fiber optical tube
- optional low-cost dedicated 0.75x focal reducer/field flattener
- nine contrast-enhancing main tube knife edge light baffles
- dual-speed 3" Feather Touch #3015 rack-and-pinion 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, the Astro-Tech 10" f/8 AT10RCF Ritchey-Chretien is now in production. The 10" Astro-Tech is the first truly affordable carbon fiber large aperture true Ritchey-Chretien astrograph available from a U. S. company. Imitators will no doubt copy Astro-Teches 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-Chretien astrographs Sky & Telescope Hot Products for 2010. (Incidentally, the original Astro-Tech 6" R-C was named a Sky & Telescope Hot product for 2009.)
The surprisingly affordable Astro-Tech AT10RCF (and its even more affordable metal tube brother, the AT10RC) joins two other Astro-Tech Ritchey-Chretien firsts. One is the AT8RC, a Sky & 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 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-Chretien 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-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 10" Astro-Tech RC 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 AT10RCF astrograph (a telescope designed specifically for photographing comparatively wide areas of the sky) makes the coma-free imaging of true Ritchey-Chetien 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, rather than aluminized Pyrex glass 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 AT10RCF provides the wide coma-free photographic field that large format CCD astrophotographers crave, but canet get from conventional reflectors and Schmidt-Cassegrains. Likewise, as a pure two-mirror system, the AT10RCF 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 & T Hot Product for 2010 Astro-Tech 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-Chretien 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 catadioptrices 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-Ces 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 Cassegraines 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; 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 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 scopees tendency to remain accurately focused after several days of inactivity during which the temperature in my backyard observatory would cycle over a huge range."
- Dual-speed 3" Feather Touch rack and pinion Crayford focuser: The precision-made Feather Touch #3015 focuser has a fine-pitch brass rack and hardened stainless steel pinion gear that are factory-matched and burnished to provide a very smooth engagement between the rack and the pinion. The drawtube glides on three stainless steel straps that mate with Teflon bearing surfaces to provide very tight yet extremely smooth motion. Using this type of design eliminates the need for grease between the drawtube and housing. A greaseless draw tube prevents the attraction of dirt that might eventually cause focusing smoothness problems. The drawtube has 13 machined internal knife-edge baffles, finished in glare-resistant matte black, to reduce reflections and improve contrast.
There are two coarse focusing knobs for focusing with either hand. The right knob also has a smaller concentric knob with a 10:1 ratio reduction gear for microfine focusing. Combined with the ultra-low backlash focuser design, this provides exceptionally precise focus control during visual observing or critical imaging. The all-metal focus knobs have ribbed gripping surfaces so they are easy to operate, even while wearing gloves or mittens in cold weather.
The 37mm (1.5") travel 3" diameter focuser drawtube has two laser-engraved scales (one on either side of the drawtube) marked in 1mm increments so you can note individual focuser positions for easy return to the approximate correct focus when switching between different imaging equipment configurations. A thumbscrew underneath the focuser body lets you adjust the tension on the focuser drawtube, in addition to letting you adjust the focuseres internal brake. A separate large knob on top of the focuser lets you lock in your photographic focus
Because the focuser is so smooth in operation and moves so freely, it can only hold a limited amount of weight (generally about 1 lb.) without drifting out of focus when the focuser drawtube is not horizontal and has a significant vertical component. The focuser therefore contains an adjustable tension internal brake system to allow astrophotography and visual use with heavy eyepieces without the possibility of focus shift.
The brake consists of a lever arrangement within the pinion block. Adjusting the thumbscrew on the pinion block beneath the focuser causes the lever to press a friction pad onto the pinion. This increases the torque needed to turn the focus knobs. If the thumbscrew is turned all the way in (only 1 to 1 turns), the pinion shaft and the drawtube are locked in position for long exposure astrophotography. Partial tightening of the internal brake offers a virtually infinite range of braking force to accommodate various accessory loads.
The focuser includes a built-in camera angle adjuster that lets you rotate the focuser a full 360Degree in a Teflon-lined track to line up a camera in either a landscape or portrait orientation (or any orientation in between) without losing focus. This also allows the positioning of objects for photography and makes the location of guide stars much easier. Three large hand-tighten knobs lock the focuser securely at the desired angle.
To fine-tune the 127mm 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 Feather Touch 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 33.6 pound weight of the AT10RCF (without extension rings), 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-Chretien 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-Chretien 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.
- 1.25" and 2" compression ring accessory holders: The 3" 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 wonet scratch the barrel of your accessories as an ordinary thumbscrew can. Three thumbscrews around the accessory holder assure a solid grip on your 2" imaging 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 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 180Degree 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 AT10RCF is protected by a two-year limited warranty against flaws in materials and workmanship.
