Astro-Tech 8-inch and 10-inch Astrographs
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8" f/8 Ritchey-Chrétien Astrograph
This Astro-Tech AT8RC Ritchey-Chrétien astrograph has:
- 8" f/8 true Ritchey-Chrétien hyperbolic mirror optical design
- low thermal expansion quartz primary and secondary mirrors, not ordinary optical glass
- 99% reflectivity non-tarnishing dielectric mirror coatings, not lower reflectivity aluminum coatings
- High strength/low thermal expansion carbon fiber optical tube, not the painted rolled steel used by competitors
- ten contrast-enhancing main tube knife edge light baffles
- dual-speed linear Crayford focuser
- 2" and 1.25" compression ring accessory holders
- two dovetail rails – one Vixen-style and one Losmandy-style “D-plate" – not simply a single Vixen-style dovetail
Features of this Astro-Tech AT8RC 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.
Optical specifications: 8" aperture, 1625mm focal length, f/8 focal ratio.
Hyperboloid primary mirror: Made of low thermal expansion quartz, rather than the ordinary optical glass used by competitors. Ground and polished under precision computer control. Unlike designs 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 AT8RC primary mirror is fixed to eliminate image shift and focus changes.
Hyperboloid secondary mirror: Made of low thermal expansion quartz, rather than ordinary optical glass. 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 AT8RC secondary mirror is fixed and focusing is done externally.
99% reflectivity dielectric coated optics: Both primary and secondary mirrors have non-tarnishing state-of-the-art dielectric mirror coatings. These have a full 99% reflectivity for the brightest possible images. This is substantially higher than the 88% reflectivity of competitors’ conventional aluminum coatings or the 94-96% reflectivity of enhanced aluminum coatings.
Carbon fiber optical tube: Made of light weight/high strength woven carbon fiber-reinforced composite material with extremely low thermal expansion characteristics to reduce the possibility of temperature-related focus changes that can occur with lesser rolled steel tube systems. Die-cast and machined aluminum front and rear cells. The 9" o.d. x 18" long carbon fiber tube is virtually indestructible. The use of a carbon fiber composite reduces the weight of the optical tube with no loss of strength or rigidity compared to a steel tube. 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. Because of the use of a carbon fiber optical tube, the weight of this 8" R-C is only a little more than two pounds heavier than the steel tube 6" Astro-Tech R-C.
Multiple internal light baffles: Computer optimized primary and secondary baffling. Ten contrast-enhancing glare-stop baffles in the optical tube; multiple glare-stop microbaffles in the secondary mirror light shield; and five baffles in the primary mirror baffle tube provide truly dark sky backgrounds during imaging.
Dual-speed linear Crayford focuser: A new design 2" Crayford focuser is threaded onto the 90mm x 1mm pitch rear cell of the AT8RC. The matte black interior of the new longer 50mm travel drawtube has anti-reflection threading for high contrast. The focuser can be rotated to any convenient angle for the sake of photographic composition by simply loosening the collar that secures the focuser to the scope body, rotating the focuser to the desired angle, and tightening the collar to lock the focuser in the new orientation.
The new bearing-less linear focuser has a polished stainless steel drive rail that runs the length of the drawtube, rather than having the stainless steel drive shaft simply press directly on (and wear) the aluminum drawtube as with conventional Crayford focusers. The drive rail rides in a self-lubricating track that extends most of the 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 less potential drawtube flexure and no wear (much less uneven wear) on the drawtube.The precision-made non-vignetting 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. Multiple internal baffles in the focuser drawtube assure high contrast.
Despite the new more rigid focuser design, the weight of very heavy equipment trains (camera, plus filter wheel, plus temperature-compensated electric focuser, etc.) may cause the 50mm long focuser drawtube to tilt slightly when fully extended, affecting the focus. Three threaded extension rings (two 1" in length and one 2") are provided to install singly or in combination between the AT8RC 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, while minimizing the need to extend the focuser drawtube. Additional optional 1" and 2" long threaded extension rings are available to fine-tune the back focus as needed, as well as optional Astro-Tech 2" compression ring extension tubes that fit into the focuser drawtube.
For exceptionally long and heavy imaging equipment trains, the standard Crayford focuser can be user-replaced by an optional Feather Touch focuser from Starlight Instruments. This requires a 90mm x 1mm pitch rear cell thread to Feather Touch adapter, available directly from Starlight Instruments. Optional MoonLite focusers from MoonLite Telescope Accessories can also be used.
Two compression ring accessory holders: The focuser drawtube ends in 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. 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 dovetail rails are provided for installing the AT8RC on an equatorial mount, as well as for mounting optional accessories (such as a photoguide scope) on top of the AT8RC. One is a Losmandy-style “D-plate" dovetail rail that runs the full length of the underside of the optical tube, for installing the AT8RC on a Losmandy-style equatorial mount. The second is a Vixen-style dovetail rail that runs the full length of the 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 Vixen-style dovetail adapters. If the AT8RC is rotated 180°, it will bring the Vixen-style rail to the bottom of the tube so it can be used to install the AT8RC on a Vixen-style equatorial mount. Competitors provide only one Vixen-style dovetail. Providing two dovetail rails on the Astro-Tech AT8RC does not limit your choice of mounts or accessory mounting options, as can happen with similar scopes provided with only one mounting rail.
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 AT8RC is protected by a two-year limited warranty against flaws in materials and workmanship.
Price $1395.00 8" f/8 Ritchey-Chrétien Astrograph
Astro-Tech 10" f/8 Ritchey-Chrétien Astrograph
Price $2695.00Developed by Astro-Tech to make large-format CCD imaging affordable for the amateur astronomer, the Astro-Tech AT10RC – a Sky & Telescope Hot Product for 2010 – is priced nearly $4000 less than the formerly least-expensive 10” R-C. The AT10RC is the first truly affordable large aperture true Ritchey-Chrétien astrograph available from a U. S. company. Even better, despite its low price, the Astro-Tech-developed AT10RC still has the premium features the larger Astro-Tech RCs are known for – quartz mirrors, dielectric mirror coatings, and more.
After several years of joint development with the manufacturer, Astro-Tech is proud to announce that the 10" f/8 AT10RC Ritchey-Chrétien is now in production. The Astro-Tech AT10RC is the first truly affordable 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 AT10RC a Sky & 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 & Telescope Hot product for 2009.)
And we are serious when we 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 & 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 AT10RC cost “about one-fourth what similar instruments did just a couple of years ago."
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-Chrétien 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 AT10RC astrograph can bring the world of professional DSLR/CCD deep space imaging to your backyard observatory at a truly affordable price.
This Astro-Tech AT10RC 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
• 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 warrantyPrice $2695.00 10" f/8 Ritchey-Chrétien Astrograph
10" f/8 Ritchey-Chrétien Astrograph with carbon fiber tube only, without focuser
Designed for exceptional imaging, the Astro-Tech AT10RCF 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 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-Chrétien 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-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.
For an interesting commentary on the true R-C design of this Astro-Tech astrograph, here’s a link to a Cloudy Nights article concerning the scope’s design from Roger Ceragioli, who was instrumental in optimizing the optical design of the Astro-Tech R-Cs. Roger is the well-known optician and optics designer who was formerly Senior Optician of the Small Optics Group at the world-class University of Arizona Steward Observatory Mirror Lab in Tucson, AZ. The “small" in Small Optics Group may be somewhat of a misnomer, as Roger’s “small" group specialized in mirrors and lenses with diameters up to a meter in size. The majority of backyard astronomers would probably consider a one meter scope to be a step up from “small," but it's small only in relation to the 6 to 9 meter spun mirrors the Mirror Lab is famous for producing for professional observatories.
Optical Specs: 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 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 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 3" Feather Touch FTF3015B-A rack and pinion, and the A30-1903-40 adapter.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.
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 won’t 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 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. 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.
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
• optional low-cost dedicated 0.75x focal reducer/field flattener
• nine contrast-enhancing main tube knife edge light baffles
• Shipped without focuser allows you to add the premium focuser of your choice
• 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
Price $2995.00 10" f/8 Ritchey-Chrétien Astrograph with carbon fiber tube only, without focuser
