Astro-Tech 6" f/9 Ritchey-Chrétien astrograph


Availability: More on the way

The exceptional value 6" Astro-Tech Ritchey-Chrétien astrograph is once again available for the serious deep space astrophotographer on a budget . .
Our Product #: AT6RC
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Product Description

This Astro-Tech AT6RC Ritchey-Chrétien astrograph has:
• 6" f/9 true Ritchey-Chrétien hyperbolic mirror optical design
• diffraction-limited or better BK-7 mirrors
• enhanced aluminum optical coatings, overcoated with quartz
• dual-speed 2" Crayford focuser
• 1" and 2" extension rings for fine-tuning the back focus
• Vixen-style dovetail rail

Developed and introduced by Astro-Tech - and named a Sky & Tel Hot Product for 2009 - the Astro-Tech 6" AT6RC Ritchey-Chrétien astrograph is back by popular demand!

The Ritchey-Chrétien optical design is used in virtually every recent large mega-million dollar professional observatory telescope - including the Hubble Space Telescope. And more "affordable" true coma-free Ritchey-Chrétiens made for schools and individuals, with prices starting in the thousands of dollars, typically come only in large apertures whose weights require a large and expensive mount to use successfully.

In contrast, the Astro-Tech AT6RC is an incredibly affordable Ritchey-Chrétien astrograph (a telescope designed specifically for photographing comparatively wide areas of the sky) that virtually all astronomers can afford! At only 12.9 pounds, it can be used successfully with a wide variety of affordable equatorial mounts or piggybacked on an existing scope - no ultra-expensive astrophotography mount required.

The AT6RC is designed for coma-free imaging using webcams, Deep Sky Imager-type cameras, and DSLRs. The December 2009 issue of Sky & Telescope said the Astro-Tech AT6RC is "a superb match" for the APS-C chips used in many DSLR cameras, "yielding a field almost 1° wide with very good star images in all but the corners of the frame." It is not designed for digiscoping through an eyepiece. Featuring a true Ritchey-Chrétien optical system, this very economical 6" Astro-Tech R-C makes you wonder just what those multi-thousand dollar R-Cs have that makes them cost so much.

The M104, Sombrero Galaxy, photo above is from Bill Bradford. He sent it to us simply with the comment, "Here is another shot with the AT6RC. Sure liking the scope." This image was named an astrophotography "Picture of the Day" on the Astronomy magazine website in July 2009.

The AT6RC lunar photo above is from an AT6RC owner, John O'Neill. It was taken with an Olympus Evolt 300 DSLR camera at 1/200 of a second through a polarizing filter. John commented, "I took this last full moon with the 6" RC. I'm very impressed with this scope. I had to collimate it a bit but after doing that the images I am getting are just superb. You certainly have a winner with this scope, at any price point."

"This may very well be the ideal scope for DSLR users," John continued. "Its fast focal ratio and wide field of view is ideal for many astro targets. I did take some shots of some deep sky objects from my light polluted neighborhood and found that the star field was pin point to the edges of my 35mm camera."

The first light image of M81 and M82 above was made by Matthew Reiche using a modified Canon XSI, an Astro-Tech AT2F field flattener, and an Orion Atlas mount. It consists of 32 five minute exposures, plus darks, flats, and bias frames, for a total exposure of 2.5 hours. It was recorded at the Jenny Jump State Park in New Jersey. Matthew said, "This was first light with my AT6RC and I think it's going to be a great scope."

Designed for exceptional imaging with DSLRs and DSI-type cameras, the Astro-Tech AT6RC provides the wide coma-free photographic field that astrophotographers crave, but can't get from conventional reflectors and Schmidt-Cassegrains. Likewise, as a pure two-mirror system, the AT6RC 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 6" aperture that equals or exceeds the light gathering of most apo refractors.

The compact size and light weight of the AT6RC, and built-in Vixen-style dovetail, makes it easy for you to mount the ascope on any mid-range equatorial mount by itself or piggyback it on your existing larger scope for imaging. An optional second Vixen-style dovetail (#AT6SDP) is available for mounting on top of the AT6RC body. This allows you to piggyback accessories (such as a photoguide scope) on top of the AT6RC if the scope is installed directly on your equatorial mount.

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 Astro-Tech AT6RC can bring the world of professional deep space imaging to your backyard observatory at a truly affordable price.

Features of this Astro-Tech AT6RC Astrograph . . .

Optical design: true Ritchey-Chrétien two-mirror Cassegrain optics, with hyperbolic primary and secondary mirrors. 6" aperture, 1370mm focal length, f/9 focal ratio.

Hyperboloid primary mirror: Made of BK-7 optical glass. Polished to diffraction-limited or better surface accuracy. Unlike catadioptric designs (SCTs, Maksutovs, etc.) that move the primary mirror to focus (which can lead to image shift as the mirror moves), the AT6RC mirror is fixed to eliminate potential image shift. The fixed primary mirror also eliminates the frequent primary mirror collimation requirements of a Newtonian reflector.

The December 2009 issue of Sky & Telescope said that the AT6RC 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."

Hyperboloid secondary mirror: Made of BK-7 optical glass. Polished to diffraction-limited or better surface accuracy. Mounted in a four-vane spider and fully collimatable.

Enhanced aluminum optical coatings: Both primary and secondary mirrors have enhanced aluminum mirror coatings, overcoated with a protective layer of quartz for long life. Reflectivity is in the 96% range, the same as the larger multi-thousand dollar R-C scopes.

Optical tube: Painted rolled steel, 7.5" o.d. x 19.25" long, with die-cast and machined aluminum front and rear cells.

Internal light baffles: Computer optimized primary and secondary baffling. Eight contrast-enhancing glare-stop baffles in the optical tube, multiple glare-stop microbaffles in the secondary mirror light shield, and four baffles in the primary mirror baffle tube provide truly dark sky backgrounds during imaging.

Dual-speed Crayford focuser: A 2" Crayford focuser is threaded onto the 90mm x 1mm pitch rear cell of the AT6RC. The 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 CCD imaging. All focus knobs are ribbed, so they are easy to operate, even while wearing gloves or mittens in cold weather.

Focuser travel: Focuser drawtube travel is 34mm, while back focus between the focuser's 2" accessory holder and the focal plane is 150mm. The December 2009 issue of Sky & Telescope said that "the infinity focus of the AT6RC falls 9-3/4" outside the back of the telescope, allowing plenty of room for all types of cameras, filter wheels, and ancillary equipment."

Two extension rings (one 1" and one 2") are provided to thread onto the rear of the scope (singly or in combination) between the scope rear cell and the focuser. These form a very rigid and tilt-free extension that moves the focuser out from the rear cell to accommodate the varying back-focus requirements of webcam/Deep Sky Imager-type cameras versus DSLRs. Typically, both rings (one 1" and one 2") will properly position most DSLRs at the AT6RC focal plane. Sky & Telescope pointed out that the "1- and 2-inch extensions, as well as conventional extension tubes that fit in the 2-inch focuser, mean that you can always assemble the system so it comes to focus with whatever camera and accessories you're using."

While it is possible to use large CCD cameras and filter wheels with the AT6RC, these cameras are generally not recommended. The weight of a standard CCD camera and the color filter wheel typically used with it may cause the focuser drawtube to tilt slightly when fully extended, affecting the focus. Adding an optional Feather Touch focuser (our part #FT-1.5BC), plus an optional 90mm x 1mm pitch adapter (our part #M90X1), will eliminate any such potential problem, although at significant additional cost (more than double the cost of the AT6RC itself).

For even more impressive coma-free DSLR imaging with the AT6RC, consider adding the Astro-Tech AT2FF field flattener. 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 of the APS-C size imaging chip used in most DSLR cameras. Use of the #AT2FF with a DSLR will typically requires one optional #AT2EXT 2" extension ring, instead of the two rings generally needed with a DSLR camera alone.

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" eyepiece holder on the eyepiece holder rotation mechanism, the 1.25" adapter also uses a non-marring soft brass compression ring.

Mounting dovetail: a Vixen-style dovetail bar runs the length of the underside of the optical tube. The dovetail can be removed, if desired, so the AT6RC can be installed in optional user-supplied mounting rings for piggyback mounting on a larger scope. An optional #AT6SDP Vixen-style dovetail is available for mounting on top of the AT6RC to allow you to mount an optional photoguide scope on top of the astrograph.

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.

Tech Details

Aperture 6"
Focal Length 1370mm
Focal Ratio f/9
Weight 12.9 lbs
Resolution 0.76 arc seconds
Telescope Type Ritchey-Chrétien
Warranty 1 year
Back Focus 150mm with focuser installed


Review by:
I'd give this 4.5 stars if that was an option as this is a beautiful instrument held back only by the complicated collimation process. Optically, this scope is excellent. It allows you to take beautiful images and is fully capable of illuminating a full frame DSLR sensor. Most of my experience with this scope is using a Nikon D610 camera and hunting summer targets like the Lagoon Nebula. Considering than even a 5" SCT costs more than this new (And I bought mine when it was still $299), it's hard not to recommend.

However, it makes you work for that with a lengthy and convoluted process of collimation, and boy will you know it if your collimation is off. A slight offset of either optic will take your images from razor sharp with beautiful diffraction spikes to a smudgy mess of blurred detail. This isn't a problem with this scope, but rather the nature of Ritchey-Chretien telscopes in general. Unlike a newtonian, you can't align one mirror and then the other. Both have to sit on the exact same axis and any adjustment to one will require a tweak to the other. This iterative process continues as you get closer and closer until both are finally aligned. I *highly* recommend a Howie Glatter laser collimator as collimation is going to be exceptionally difficult without one. And for the love of all that is holy, don't even think about turning that phillips head screw that that holds the secondary in place. (Posted on 2/20/2021)
Review by:
Just started using this scope for astrophotography after a year of visual observation and it exceeds in both arenas. For someone just getting into astrophotography, you will be hard pressed to find better at this price point. Highly recommended. (Posted on 10/31/2019)
Review by:
I purchased this astrograph originally for photography. It quickly became my scope of choice for viewing. In fact I haven't taken a photo yet. Set up with a 2" dielectric diagonal mirror, it is a massive view for the price! I love it! (Posted on 10/17/2019)
Review by:
Got mine for $299 and got back to AP after a long hiatus. I could not believe the price. Used with DSLR 5D/6D/T7i. Zwo 174/ 290/071. From the 2017 Eclipse, Super Blue Moons w/ISS transits, Deep sky, and planetary ( powermate5x/zwo290) , this scope did the job. I've used it with .8 FF with SLRs, without FF with the zwo. Fast, sharp, inexpensive. great value.
I did upgrade to a linear bearing crayford and rigel auto-focuser. (Posted on 10/4/2019)
Review by:
This was the first real telescope I ever bought. I am a photographer from way back, but hadn't done much astro stuff. Seeing this on sale a few years ago gave me the impetus to get something other than a telephoto lens, and I am soooo glad I did. My first pics were of the moon, and I then moved up to M51, M101 and the Horse Head nebula, all with this scope. Love every minute of it, especially for the price... (Posted on 8/28/2019)
Review by:
Love my AT6RC, great for wider field astro imaging. Mounted on an Explore Scientific EXOSII PMC8 makes it a great little goto rig. Five Stars! (Posted on 8/22/2019)
Review by:
What a great telescope! I only used it at f/9 but it was still a delight to use. It did a great job worth star clusters and other deep sky objects. (Posted on 8/14/2019)
Review by:
An affordable RC scope for deep sky imaging or galaxies and planetary nebula. No need for field flatterers or coma corrector. Light weight for the aperture . A good astrophotography scope. (Posted on 7/31/2019)
Review by:
This is a great scope for the money. I purchase it when it was $299. You will need the extension tubes for visual observatory. The Astro Tech field flattener is worth the expense. I have used it for planetary, double stars, and solar observing. Work well with my Nikon D5000-series DSLR. The focal reducer will be my next addition. The optics are superior. It is relatively light weight. (Posted on 7/22/2019)
Review by:
I bought this to try some longer focal length astrophotography. It covers the chip of my APS-C mirrorless camera very well. The focuser holds my small (original EOS-M) camera fine, but others have had trouble with larger camera with filter wheels. I use the AstroTech AT2FF field flattener and it improves the stars at the edge. I bought a $25 tool box at Lowes, made some padding with pipe insulation, and now have a fine case for it. It's a great introduction to AP so you can put more resources into a higher quality mount. Considering one of the larger versions when my skills improve. (Posted on 7/22/2019)
Review by:
I couldn't be happier with my AT6 RC. I use it on my travel setup along with my TMB 92 SS to give me a little higher power for planetary work. The quality of the Optics is unbelievable for an RC scope in this price range. I don't know how Mike and crew do it. (Posted on 1/10/2019)
Review by:
Bought this a while back and have been rather impressed with the quality. I use this with my Celestron AVX mount and am able to pull off some rather impressive captures. Easy scope to justify and much better than my previous Celestron 6in. I would suggest buying this if this is your first imaging scope. (Posted on 1/7/2019)
Review by:
I picked up an AT6RC several years ago and I was so impressed I bought the 8" RC with the carbon fiber tube. The OTA was rugged and held collimation well. (Posted on 1/3/2019)
Review by:
Excellent scope for both visual a photo. and great price also (Posted on 12/30/2018)
Review by:
I've owned the AT6RC for about 5 months now, and am very satisfied with the image quality on an APS-C sized sensor as long as the scope is well collimated, and a flattener is used. Collimation is quite difficult and I recommend the focuser flange, and Bob's Knobs to all users as accurate alignment of the optics can take several hours, and is best done using CCD tools to check stars for coma and astigmatism. (Posted on 12/22/2018)
Review by:
My intro to Astrophotography started with this scope. I found it very forgiving as I used it on a CG-5 mount starting out. With the mount I was limited to under 2min for exposures and was very impressed with images I was able to capture, I have two printed out in my office that get many comments. (Posted on 11/20/2018)
Review by:
I have had my 6" RC for a couple years now. No problems during this time. It has been well thought out for use with astrophotography and I am very appreciative of the included spacer rings necessary for my camera set up that includes a 0.7 focal length reducer. I agree with other reviewers and their setups, that a longer dovetail is needed. After a couple of years of use and being hauled around on some pretty rough roads, I am surprised it has held up so well, especially the collimation. (Posted on 11/18/2018)
Review by:
Excellent views and the "best" for astro-photography! Crystal clear! You can't beat the price as well!! (Posted on 10/31/2018)
Review by:
I've had one of these since the were on sale a while back for $299.
The RC design , without the front mounted corrector plate, is less likely to dew up and in the Pacific Northwest that's a great feature. I use this tube mostly for astro imaging and have had excellent results on long exposure photos. Even at higher cost than I paid this is a great value as there is little in it's price range that compares. (Posted on 10/29/2018)
Review by:
Once you get this guy collimated and a good reducer to go with it, this ota will become your new best friend in the world of longer focal length (Posted on 10/17/2018)
Review by:
I simply cannot get enough of this telescope. It is my favourite for deep-sky imaging portability with such a graceful amount of aperture. The telescope is quite lightweight, and mounts easily. Using all the extenders that came with the telescope helped my DSLR camera to reach focus. All in all, a great telescope for astrophotography. (Posted on 10/16/2018)
Review by:
This scope has been a part of the imaging line up at Fox Park Observatory since it's introduction. Me and multiple members have used it on a lot of small mounts like the AS-GT and the AVX. It has worked very well on all of them. Only think I would changed is adding a focus lock like the AT8RC. Great scope at a great price to get started in longer focal length AP. Recommended. (Posted on 10/8/2018)
Review by:
This scope performs excellent at the price point. I purchased it as an entry level and it has kept me going because it performs so well. Captures fantastic light with both my DSLR and my CCD. (Posted on 10/7/2018)
Review by:
I've been using this scope for more than a year now. Initially I used it with the field flattener at F9, and the focal length was quite long for my AVX mount to handle. I then seriously stepped up my game with this scope by adding a CCDT67 focal reducer taking the it down to F6 at around 915mm focal length. This is really a nice combination. I get pinpoint stars across the entire field, and imaging with this scope now provides some excellent results. Color and clarity are great, and it's easy to manage with an entry level mount like the AVX. (Posted on 10/7/2018)
Review by:
Bought the AT6RC for the purpose of improving my pictures. Best buy I have ever made. (Posted on 10/7/2018)
Review by:
I've used this scope exclusively for visual observing so far. I was afraid it would be too heavy to use on my Celestron NexStar 6SE single fork mount, but no problems there. That mount does limit the Astro-Tech's range to about 60 degrees altitude, however, due to the length of the optical tube, so I see a new mount in my future. At F/9, the Astro-Tech's rich, flat field compares favorably with my NexStar 6SE, but its main attraction for me was its incredibly low price for a telescope of this size and quality. (Posted on 10/6/2018)
Review by:
The telescope is easy to handle, it has good image quality and the optics are fine. However, the focuser does not perform very well. When the tension screw is tightened, takes the focuser out of collimation. (Posted on 8/4/2017)
Review by:
I bought this about 4 months ago, and only recently have i had a chance to really try it out. Put it on my atlas mount, and with no guiding, took a bunch of 30 second unguided pics, and stacked them in DeepSkyStacker. Wow, if i can do this well without really trying, without accurate polar alignment, I cannot wait to see how well this little baby will do when I learn how to use it. I'm using it with a canon xsi, and i'm using it with a russian extension tube that has a t-thread on the end of it, so that may help with the focuser rigidity, or just the fact that i don't have a bunch of heavy gear hanging off it, but it has done fine so far. All in all, I'm very pleased with my purchase, and am looking forward to years of astrophotography with this scope. (Posted on 8/4/2017)
Review by:
I have had this scope for a couple years now and really enjoy using it. I have used it primarily with my Canon 20D for Astrophotography. I have used it with my QHY5 Planetary/guider camera on Jupiter and Saturn. The large secondary does rob some of the light and contrast on solar system objects though. The size of the OTA is great for medium sized mounts, but I would still recommend a CGEM size mount for Astrophotography, for that added stability. (Posted on 8/4/2017)
Review by:
These are really nice. I've used one of these just about every clear night since buying one on sale. Living near Saint Louis, these telescopes are amazing since they *never* dew or frost up due to the design. I've used mine at 0 and 100F with 90 percent humidity. I've liked this one so much that I picked up an AT8RC when I saw one come up for sale.

If you do decide to go for one of these, I highly recommend buying a good focuser since the stock one doesn't handle weights well. I've been using an automated Moonlight 2.5" setup for a couple years with no issues. This setup can easily hold my ST-8300M, OAG with ST-i, and AT2FF. (Posted on 8/4/2017)
Review by:
5 stars from me. I too jumped on the AT6RC when it was on sale for $299.00. It's a steal at $499.00. The price:performance ratio is almost untouchable. My comparable scope is a C6. I know it's not the same type of scope, but they both have 6" apertures. The biggest factor is the contrast. Image quality is great. I have no issues with this OTA. (Posted on 8/4/2017)
Review by:
This is a surprisingly good scope for the money. At $499 it is a bargain. At $299 it was a steal. It seems overkill to add a Feathertouch focuser to a $499 scope but so worth it. It is an RC so it is meant for rich field imaging. I have found that it also makes a good visual scope. I would use it with a DSLR and save for the 8" carbon fiber RC. You will need front side counterweights or have a very long dovetail to balance it. I found I needed to add just a couple of pounds to a lower side of the dovetail with a Losmandy Vixen style bracket. The Celestron version usually mentioned in accessories is also a good option. One issue I did have using the existing focuser is that it started to unthread from the scopes backing plate when I rotated the focuser. A drop of blue Loctite may assist you here so it is still possible to remove it without destroying it when you move from a visual back to an imaging setup where you add some of the extension tubes available. I used 2 of the 1" spacers. (Posted on 8/4/2017)
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Supplied Accessories

• 1" and 2" extension rings for fine-tuning the back focus
• Vixen-style dovetail rail