Astro-Tech 2" Field flattener for imaging with Astro-Tech and TMB refractors


Availability: Out of stock

The Sky & Telescope Hot Product for 2010 Astro-Tech 2" photographic field flattener improves the image sharpness at the corners of the field with Astro-Tech and TMB apo refractors, but will also work well with any other brand of f/6 to f/8 refractor, as well as Astro-Tech Ritchey-Chrétiens . . .
Our Product #: AT2FF
Astro-Tech Product #: AT2FF

Product Description

New for August 2021, thread on adatper tops to choose between 42mm T-threads and 48mm T-threads.

Named a Sky & Telescope Hot Product of the Year for 2010, the Astro-Tech photographic field flattener reduces the normal field curvature inherent in all refractors to provide you with images that are sharply focused out to the very corners of your DSLR or large format CCD imager frame. Stars on your images look sharp and point-like all the way across the field. You don't have to worry about photos that are sharp in the center but out of focus at the edges. The field flattener also works surprisingly well with the 6", 8", and 10" Astro-Tech Ritchey-Chrétien astrographic reflectors.

As Sky & Telescope pointed out in their Hot Product citation, "With only a few noteworthy (and expensive) exceptions, refractors need optional field flatteners in order to deliver acceptable star images across the field of today's DSLR cameras. Custom-designed flatteners usually cost hundreds of dollars, but the Astro-Tech 2" Field Flattener is only $139. Furthermore, it's designed for any refractor with a focal ratio between f/6 and f/8. And there are reports that helps flatten the field of Astro-Tech Ritchey-Chrétien astrographs. The flattener was reviewed in the September 2009 issue of Sky & Telescope, page 38."

Designed to work purely as a field flattener for imaging, and not simultaneously as a focal reducer or telecompressor, the 2" Astro-Tech field flattener does not change the focal length or focal ratio of your telescope. It is not designed for visual use, having photographic T-threads only and no provision for using a star diagonal or eyepieces.

A separate review in Sky & Telescope magazine of the Astro-Tech field flattener and the Astro-Tech AT106 refractor said the field flattener was "extremely easy to use with any SLR camera. You simply screw on the appropriate T-ring, connect your camera, and slip the flattener into the AT106's 2-inch focuser. Daylight shots made two things immediately apparent - the field flattener does not change the telescope's focal length (it's a true zero-power flattener), and it sharpens images at the edge of the field . . . At night, star images in the corners of my Nikon D300's APS-format frame, while vastly better than those recorded without the flattener, still showed a slight elongation . . . By focusing at a point slightly off center, thus balancing the imaging performance between the center and edge of the field, I could fill the frame with nice, round star images. For photographers shooting day or night, the flattener is well worth its current $150 price."

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. Comments like "Works great on my AT8RC. Won't image without it," and "Works well with my AT6RC," show up regularly in on-line imaging forums. 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 design of the Astro-Tech Ritchey-Chrétiens. 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")."

The 2" barrel of the fully multicoated dual-element Astro-Tech field flattener inserts directly into your scope's 2" focuser drawtube. A groove machined into the field flattener barrel engages the thumbscrew or compression ring of your focuser to act as a safety stop. This prevents the field flattener and camera from falling to the ground should the thumbscrew or compression ring accidentally loosen during use.

The AT2FF now comes with threaded adapter tops for 42mm x 0.75mm pitch , or 48mm x 0.75mm pitch, T-2 photographic T-threads on the observer/camera side of the black anodized field flattener accept a standard T-ring for connecting a 35mm or DSLR camera to the field flattener. They also allow direct connection to many CCD camera/color filter wheel combinations.

Spacing from field flattener to film plane: Optimal spacing from the shoulder of the field flattener (where a T-ring threads on) to a camera's imaging sensor or film plane is 57mm +/- 4mm. The following DSLR camera body/T-ring combinations typically all fall within this optimum spacing range and generally should require no additional spacers.

A Canon EOS DSLR/T-ring combination typically has a T-ring front flange to camera sensor spacing of approximately 55.5mm, although this number is dependent on the thickness of the T-ring you use and cannot be guaranteed. (Without T-ring, the distance from the front flange of the camera body to the sensor is approximately 44mm by itself.)

A Minolta/Sony DSLR and T-ring combo typically has an approximately 54mm T-ring front flange to sensor spacing. The exact number is again dependent on the thickness of your T-ring. (The camera front flange to sensor distance by itself is approximately 43.5mm.)

A Nikon DSLR and T-ring combo typically has a total spacing of approximately 56mm. This number is again dependent on the T-ring thickness. (The camera front flange to sensor spacing is typically 46.5mm by itself.)

With CCD and DSI-type cameras, some experimentation with spacers will be necessary to achieve optimum performance, as these typically have much shorter camera front plate to sensor spacing than DSLR cameras.

Tech Details

Weight 8 oz.
Warranty 1 year


Review by:
The factory applies adhesive to the nosepiece threads. Using a rubber mat-style jar opener, I was able to loosen and unscrew the nosepiece revealing an M48 female thread. I used my fingernail on the remaining residue on the threads and a vacuum to get any loose flakes of residue out. Do this entire operation with the nosepiece facing down to prevent the residue from falling on the lens or into your telescope. (Posted on 1/26/2021)
Review by:
I use this for my Explore Scientific AR152 refactor, F6.5 and it works very well at providing a flat field all the way to the edges. I would recommend it for any refactor especially if you are planning on doing astrophotography. (Posted on 8/27/2019)
Review by:
I finally had the chance to buy this product and I will say that I am indeed happy with my purchase. I pair this field flattener with my Astro-Tech AT72EDII Refractor OTA FPL-53 f/6. Last night I finally got a chance to image the Orion nebula for the first time because it was finally a clear night and I am very happy with using this field flattener because the whole image from the middle to the outsides were flat, to when not using this the corners wouldn't be as flat as the middle. Definitely recommended! (Posted on 1/6/2019)
Review by:
This is a beautifully made and coated optic! I've used this with great results on the sweet little AT60ED and also the AT72ED. I'm using M43 and see excellent stars to the edge. I have a friend using the AT2FF on an AT72ED with a Canon 6D full-frame and he is also very pleased with the results! (Posted on 1/3/2019)
Review by:
I have had one of the AT2FF since I got my first RC. It works well with my 6, 8, and 10"RCs and it works very well with my Explore Scientific 127EDT, Orion ED80 and my Williams Optics 80mm ED. I will be keeping this for a long time. (Posted on 1/3/2019)
Review by:
As a "plug and play" reducer it works reasonably well with APS-C sized sensors on both RCs, doublets, and triplets. You may need to get some very small spacers to fine tune spacing depending on your optics and how particular about edge stars on APS-C sensors but smaller sensor will be ok at the recommended 55mm. Larger full frame sized cameras would be better served by a higher end reducer. (Posted on 12/22/2018)
Review by:
I bought the Astro Tech flattener to use with several telescopes, but it ended up getting first light at the tail end of a 130mm f/6.3 apochromatic triplet with a 28mm chip DSLR. As it turned out, the flattener worked perfectly on the first try- as easy to use as if it were a plain nosepiece. However, the images were a pleasant surprise as stars in the corners of the frame lost their minor bloating and the entire field took on that last bit of crisp focus which had eluded me until then. As a side benefit, installing 2” filters is just a matter of screwing them on to the front end just like an eyepiece. So, if you aren’t using one of the enormous detectors out there and don’t quite have the budget for a $1000+ flattening system with complex camera attachments to support gear you don’t own, this flattener makes a lot of sense. (Posted on 12/7/2018)
Review by:
Purchased this, so I could use my home-built 90mm f/5.5 refractor with my full-frame DSLR. The flattener works well, even when pairing an fast achromat with a big full-frame sensor; giving nice round stars across the field. I also enjoy the fact that it's a true 1x field flattener ... my telescope's focal length is short enough as it is! Highly recommended! (Posted on 11/17/2018)
Review by:
I bought this flattener to pair with my AT72ED and my Orion EON 110 scopes. I was reluctant at first because of the price compared to other more well know names that also make flatteners. I have used this flattener on both of my scopes many times and would highly recommend it.
The unit is well made and performs extremely well. There are dust covers for both ends of the flattener when not in use.
The unit is used with both of my scopes along with a Canon 450D, and a ZWO 1600mc camera, with no more cropping the images to remove the elongated stars. I am extremely happy with the flattener. (Posted on 11/11/2018)
Review by:
Good advice and fast service! Having procured a used TMB 92ss I called astronomic‘s and asked them what they would suggest a good field flattener or filled reducer to purchase for this long out of production scope. The Astrotech 72 mm field flattener was what they suggested.

So I ordered.

I received the 2 inch field flattener within days of purchase and have not been disappointed. This is a great match up for this highly curved field exquisite refractor. Although the product does not match the advertised picture, it is even better when held. The large bright Astrotech lettering is now gone and a new ergonomic Grip has been added.

This field flattener is a must have for Any at 5.5 telescope Astrophotographers! (Posted on 10/26/2018)
Review by:
Used it on my AT111EDT and my Canon 6D. Screwed straight onto the T-ring of the camera with the right spacing. Loved it. (Posted on 10/25/2018)
Review by:
This flattener was highly recommended to me by several people using scopes of different optical design. It works for both refractors and RCs. I use it on my Explore Scientific 102mm FCD-100 APO refractor and get an excellent flat field of view with about 57mm of spacing from the sensor on my ASI1600MM-Pro. It gives me just the right field of view at my scope's native focal length for those smaller objects. (Posted on 10/24/2018)
Review by:
I bought this as a recommendation here on the site to pair with my 8RC, and I must say it works perfectly! I get a nice flat field edge to edge using my DSLRs with a T ring screwed directly on it. What more could I ask for? It's perfect! If you have an RC I would highly recommend getting one of these for it so you can shoot at the native f/8. (Posted on 10/15/2018)
Review by:
I bought the AT2FF for the AT115EDT. It makes a flat field up to the edge. Stars are sharp up to the corners on a APS-C sensor. Works flawlessly, I highly recommend it. (Posted on 10/11/2018)
Review by:
I have used this with great results on both my AT111 and my AT8RC. Check out my images at for more details. Spacing perfect for my Canon DSLR with the T-Ring and stars are very sharp. Well worth the money! (Posted on 10/9/2018)
Review by:
this field flattener makes your stars a perfect roundness up to the edge very good buy and especially for the price (Posted on 10/7/2018)
Review by:
Works super well with my AT72ED II and DSLR, very pleased with the stars I am getting. I would definitely recommend, it's essential for using the full frame of your photo without having to crop (Posted on 10/6/2018)
Review by:
I bought it used from a friend and I love it! I use it with my Orion 80ED f7.5 refractor and a Canon T2i. Stars are pinpoint to the edge of the field. (Posted on 8/4/2017)
Review by:
I bought the AT field flattener when I bought my AT72 ED. What a great pair! With a DLSR, you can get alot in the field of view with these two(i.e, M81 and M82). Stars are very sharp from edge to edge. Well worth adding to your refractor. (Posted on 8/4/2017)
Review by:
This flattener is fantastic. I've used it with both an Astro-Tech AT6RC and an Astro-Tech AT90EDT with round starts to the corners using a SBIG ST-8300M. All you have to do is make sure you have the spacing from your imaging chip to this flattener 57mm +/- 4mm. This works out of the box for most DSLRs. (Posted on 8/4/2017)
Review by:
This is a must have if you have the Astro-Tech 72mm. Wow do these optics perform nicely with that scope. Images are crisp and flat to the edges. Well done, astro-tech, well done indeed! (Posted on 8/4/2017)
Review by:
I replaced another manufacturer's more expensive 0.8x flattener (did funny things to the stars at the field edges) with the Astro-Tech 0x flattener and I'm extremely happy with the results. First, it does not change your focal length and really does flatten the field. Perfect combo for imaging with my Vixen 102mm f6.5 ED refractor. I HIGHLY recommend the flattener with any short focal refractor plus the products & service are top notch at ASTRONOMICS! (Posted on 8/4/2017)
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