Most photographers are pretty familiar with the concept of a teleconverter. Basically, it works by magnifying the image circle projected by a lens, then refocusing the light so you can still get an in-focus picture despite the lens now being farther away from the camera. This is often an affordable way to turn your 200mm lens into a 400mm lens, but it does come with some downsides: namely, a potential loss of sharpness and a definite loss of light. The sharpness issue may or may not be noticeable to you depending on what you’re shooting and how you plan to display it, but the stop to 2 stops of light lost due to a teleconverter can definitely be problematic. Still, it is a compromise often worth it.
But what if you wanted to go the other way around? What if you wanted to take a lens and make it wider and, by doing so, brighter? In truth, this is not a new concept, and such a thing has been on photographers’ wish lists since the film days. Unfortunately, there just wasn’t a good way to do it. If you take a lens and shrink its image circle down, it will no longer fill the frame. Secondly, whereas a teleconverter moves the lens farther away from the body, a wide-converter would have to do the opposite, potentially pushing up against the mirror in an SLR. While theoretically it may have been possible to do this with a medium format lens on a 35mm camera, the market for such a thing probably wasn’t big enough to warrant its manufacture. However, thanks to the proliferation of mirrorless digital cameras with smaller sensors and the abundance of used, inexpensive full-frame lenses, the market is now there to support such a device.
Enter the Metabones Speed Booster. Essentially the opposite of a teleconverter, it promises to make your lenses wider (by a factor of 0.7) and a full stop brighter. And whereas a teleconverter loses sharpness because it magnifies any aberrations of a lens, Metabones claims the Speed Booster reduces aberrations just as it reduces the size of the image circle, thus improving sharpness. Now, I’ve seen some tests, and in all honestly I can’t back up the claim about improved sharpness—maybe in ideal conditions with ideal lenses this is true. I can, however, say that the other claims are absolutely spot on: the gains in field of view and transmission are very noticeable. One caveat: there are limited combinations of lenses/bodies that will work with the Speed Booster, and it must be a larger-format lens going to a smaller-format, mirrorless body. Right now, adapters are available or are coming soon for Leica R, Canon EOS, and Nikon F to Sony E, Fuji XF, and Micro Four Thirds. Due to mirrors getting in the way, Metabones can’t make a Speed Booster for APS-C DSLRs.
I own a Panasonic Lumix GH3, which I use primarily for video. The Speed Booster is fantastic here. If there is any loss of sharpness, it won’t show up in a 2MP video image, but the increased angle of view and brightness definitely helps make up for the inherent shortcomings of shooting on the Micro Four Thirds format. In fact, when using the Speed Booster, the GH3’s frame size becomes equivalent to the Super35 cinema format—this is absolutely perfect for video shooters. If you own a Sony NEX or Fuji X series camera, using the Speed Booster with a full frame Nikon, Canon, or Leica R lens means you no longer lose field of view; you can ignore your “crop factor” completely. You also gain the low light capabilities of a full frame sensor. For example: a 50mm f/1.4 lens mounted on a Sony NEX camera via the Speed Booster will essentially become a 35mm f/1.0 lens, yielding the same field of view and light gathering characteristics as if the lens were mounted on a full frame camera.*
So, is the Metabones Speed Booster for you? Keep in mind, like with most lens adapters, you will not be able to use autofocus or autoexposure with the Speed Booster. For me, that isn’t a problem. I’d say for anyone shooting video on the MFT system, including the Blackmagic Cinema Camera and Pocket Camera, the Speed Booster is more than worth it. Similarly, if you shoot an NEX or Fuji X series camera and long for the low light and shallow depth of field capabilities of a full frame sensor, the Speed Booster will get you there. It is also one of the best built adapters around, with very solid mounts on both the lens and body side. If you are a stills shooter concerned about maximum sharpness or autofocus, however, you are probably best sticking with the lenses made for your system.
The Metabones Speed Booster is currently available to order in Canon EF to Sony E, Nikon F to Sony E, Nikon F to MFT, Nikon F to Fuji XF, Leica R to Sony E, Leica R to MFT, and Leica R to Fuji XF. Prices start at $429.99.
*If this doesn’t make sense, here’s the math: [focal length] x [Speed Booster multiplication factor] x [crop factor of camera format] = [full frame equivalent]. So, 50mm x 0.7 = 35mm. 35mm x 1.5 [NEX crop factor] = 52.5mm. The same is true for aperture: f/1.4 x 0.7 = f/0.98. F/0.98 x 1.5 = f/1.47. Notice the final numbers aren’t exactly the same as the starting numbers, but they are close enough that it shouldn’t make a difference to most photographers. Coincidentally, Speed Boosting a lens to MFT will yield roughly the same field of view and transmission as a non-Speed Boosted APS-C sensor. And I just verbed a noun.