Metabones Speed Booster lens adapter for mirrorless cameras increases apertures, sharpness


Metabones and Caldwell Photographic introduced today the Speed Booster lens adapter that mounts between a mirrorless camera and a SLR lens. The adapter increases the maximum aperture by 1 stop, it also improves MTF, sharpness and has a focal length multiplier of 0.71x. To learn more details about this new prodcut, read the Speed Booster White Paper on Metabones' web site:

The amount of focal length reduction and speed increase can be calculated by the magnification of the focal reducer. So, if the focal reducer has a magnification of 0.7x, then the focal length of the new system is 0.7 times the original focal length of the objective. Similarly, the f/# of the new system is 0.7 times the original f/# of the objective.



  • Magnification: 0.71x
  • Maximum input aperture: f/1.26
  • Maximum output aperture: f/0.90
  • Lens elements/groups: 4/4
  • Objective lens mounts: Canon-EF, Nikon-F (Leica-R, Contax C/Y, Contarex and Alpa planned)
  • Capabilities, Canon-EF version: Electronic iris control, AF and VR
  • Capabilities, Nikon-F version: Manual iris control of G type lenses
  • Camera mounts: Sony NEX, Micro Four Thirds, (Fuifilm X planned)
  • Length reduction (Sony NEX, version): 4.16mm
  • Length reduction (Micro Four Thirds version): 6.17mm
  • Dimensions Sony NEX version (diameter x length): 69mm x 27mm (with tripod mount removed)
  • Weight Sony NEX version: 194 grams
  • Tripod mount: Removable type with Arca Swiss compatibility

Metabones Speed Booster lens adapter

Press release:

Petersburg, VA, USA, January 14, 2013 - Metabones® and Caldwell Photographic jointly announce a revolutionary accessory called Speed Booster™, which mounts between a mirrorless camera and a SLR lens. It increases maximum aperture by 1 stop (hence its name), increases MTF and has a focal length multiplier of 0.71x. For example, the Canon EF 85mm f/1.2L II lens becomes a 59mm f/0.9 lens on a Sony NEX camera, with increased sharpness. The faster F-stop allows for shallow depth-of-field and a lower ISO setting for decreased noise.

Speed Booster is also particularly pertinent to ultra-wide-angle SLR lenses. The combined focal length multiplier of Speed Booster and an APS-C mirrorless camera is approximately 1.09x, making the combination almost "full-frame". Full-frame ultra-wide-angle SLR lenses largely retain their angle-of-view on an APS-C mirrorless camera when Speed Booster is used.

The optics of Speed Booster is designed by Brian Caldwell, PhD, a veteran of highly-corrected lens designs such as the Coastal Optics 60mm f/4 UV-VIS-IR APO Macro lens with exemplary MTF performance (focusing done with visible light requires no correction whatsoever for the full spectrum from UV to IR).

Speed Booster serves double-duty as a lens mount adapter, from Canon EF lens (but not EF-S) to Sony NEX, with auto-aperture, image stablization, EXIF and (slow) autofocus support for late-model (post-2006) Canon-brand lenses. It will be available in January 2013 from Metabones' web site and its worldwide dealer network for US$599 plus shipping and applicable taxes and duties.

Other mount combinations will follow shortly afterwards. Leica R, ALPA, Contarex, Contax C/Y and Nikon F (with aperture control for G lenses) will be supported, as will Micro 4/3 and Fuji X-mount cameras. Support for other mounts will be added in the future.

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  • why cant they do this for medium format lenses and get them to fit on fx

    • Lio

      Because it’s baloney, and when you go for high product (FX) dedicated to pro or fanboy it’s more difficult to sell it. You can’t add sharpness by adding lens element when you don’t control the overall optical formula. As well you can’t increase f stop by adding optical element. It’s just marketing baloney because f-stop is always the focal length divided by the lens diameter…

      • bjrichus

        It does run counter to all the physics doesn’t it? How can you add light transfer through the system by putting something in the way of the light path (another element)? Unless there is some magic dust being left in there by the pixies, I tend to agree with you Lio.

        By the way, the definition of f-stop on Wikipedia has it as being: “the ratio of the lens’s focal length to the diameter of the aperture (or entrance pupil)” not the lens diameter (a difference of terminology, but you don’t say if you mean the diameter of the lens barrel, inside or outside etc…

        • tanner

          I love how many “experts” there are that think they know everything about a product – good or bad – why not just say “I’m dubious but let’s see what the tested product can do once it in the hands of photographers?”

      • tanner

        Lio must have woke up on the wrong side of the bed. I am looking forward to high res samples but the images in their white paper are impressive. Seems pretty plausible to me – reductions always improve perceived sharpness so why wouldn’t this concept translate here? Just because you are adding elements to the rear does not mean they have to reduce overall IQ. If you get a natural improvement from reduction and the optical aberrations introduced by the elements are not as great as the reduction benefit, than you have an improvement. That 35mm Nikor sample on m/43 in the white paper looks outstanding.

      • M

        Only they know about the difference in sharpness, but you can too increse the f-stop in exactly the way you describe! The converter decreases the focal length of the lens, just in the opposite way of a tele-converter, without changing the diameter, hence increasing the f-stop of the lens+adapter kit. This has been done before by lens makers, the Olympus 35-100 f/2 4/3 lens is practically a 70-200 f/2.8 FX lens with a focal length reducer built in.

        • Setani

          Nice historical observation. Do you know hoe these Olympus lenses performed against each other? In theory, the “reduced” version should be much better than the FX one…

      • peevee

        They decrease effective focal length while concentrating the same light on smaller circle. No wonder the light intensity grows (f-number decreases).

  • Looks like fun to me! Too bad I don’t have a mirrorless camera…

  • theRBK

    the greatest utility of this is probably to use an FX lens on a DX camera (especially a mirrorless one) at close to the FX lens’ original angle of coverage on an FX camera… it’s basically a reverse of what you get on a teleconverter (you could call it a wide converter, similar, but not identical effect, to those that you screw in front of a lens… not exactly a new idea)… don’t know about the claimed “increase MTF and sharpness”; increase compared to what?… about the “increase” in maximum aperture, it’s basically returning you the light that was not used when you mount an FX lens on a DX or smaller sensor, ie. the light that was transmitted through the lens and might have been picked up by an FX-sized sensor that covers most of the image circle of the lens but not picked up in a smaller sensor that only covers a smaller part of the image circle of the lens…

    • Discontinued

      You didn’t get it. Unless you are kidding.

      • fiatlux

        He more or less got it. A rear focal reducer basically converges the light rays exiting from a lens on a smaller target, Exact oposite effect as the diverging group of a TC. Of course, the lense has to have a larger coverage than required to start with, or it won’t work.

        This is nothing new in fact, and I remember one of the first Nikon DSLR, the Nikon E2/3 having such a converter (with many restrictions, due to the reflex design).

        The claim of improved MTF may seem odd, but the white paper explains why this is so (hint: in the center, not in the corners).

        Clever product. Not cheap, but probably worth the price when compared to a Voigtländer 35mm 0.95 for instance.

  • Soma

    Any idea if it alows us to use an FX lens on a DX reflex camera or it’s just for mirrorless ones? ’cause in the first case it can be really interesting

    • soma

      my bad, just got my answer :s

  • Sahaja

    Looks interesting. I cant wait for the F mount version.

  • mythbuster

    Nothing is for free. I am a little skeptical about this. Let´s wait pro reviews, but probably final imaging quality is not very good with high geometric distortions and chromatic aberrations.

    • fjfjjj

      You’re right that nothing is for free. In this case, you give up coverage (image circle diameter) and focal length, and gain an f/stop.

      • mythbuster

        Ok, but also put a converging lens (a magnifying glass), between the FF lens and the sensor. This for sure is not good for improving imaging quality (distortions and aberrations).

      • It’s wrong to say you’re giving up coverage with this adapter… you’re actually utilising the whole image circle… so it’s definitely a plus.

        The reduction in focal length is countered by the crop factor… so you get the same sort of field of view you get on FF.

  • camerageek

    OK, so something that has been available to astrophotographers for nearly 40 years (they call them telecompressors) is now available to regular photographers….yawn

    • fjfjjj

      Yeah, it’s like with low noise sensors, high capacity rechargeable batteries, and color LCD screens. All of these things were available to specialists before they were put in consumer digital cameras, so I don’t care about them. *snark*

      • camerageek

        Amateur astrophotographers peasant! You could buy these frome Meade or Celestron for ages. Not exactly NASA. Now kneel and keep your jhead down when speaking to me knave!

    • 400yrs

      the speed booster is available as adapter to use with mirrorless camera only.
      and mirrorless camera became popular just within these few years.
      that is why only now the focal reducer became available to regular mirrorless camera photographer, and not 40 years ago.
      there is no consumer mirrorless interchangeable camera 40 years ago.

  • Ben

    Nikon did this when they first entered the digital realm, in collaboration with Fujifilm.

    These cameras had a tiny 2/3″ sensor, used Nikon F-mount 35mm lenses, but had a 1x crop factor because of their reducing optics. In this case, the optics increased the effective f-stop by 4 stops.

  • Too bad it’s priced in the same ballpark as a Canon EOS M body…

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