Metabones and Caldwell Photographic have jointly announced a revolutionary accessory called Speed Booster, which increases the maximum aperture by one f-stop and reduces the focal length of SLR lenses by 0.71x when they are mounted to mirrorless cameras.


The new Metabones Speed Booster. (Source: Metabones.)

The optics of Speed Booster is designed by Brian Caldwell, PhD, a veteran of highly-corrected lens designs. The initial product, which has been designed to enable Canon lenses to be mounted to Sony NEX camera bodies. It will be available from the Metabones’ web site and its worldwide dealer network for US$599 plus shipping and applicable taxes and duties.

The main purpose of the Speed Booster is to act as a focal length reducer, enabling users of mirrorless cameras to overcome the sensor’s crop factor and allow wide-angle lenses to work at close to their marked focal lengths. (A major problems with mirrorless cameras has been a lack of true wide-angle capabilities, imposed by their smaller sensor dimensions.) The relatively short flange-back distances in these cameras, however, have made the development of compact focal length reducers possible. With the first product, a Canon 50mm f/1.4 lens becomes a 35.5mm f/1 lens on a Sony NEX.

But that’s not all; the focal length reducer also reduces the size of many common lens aberrations, providing some gains in resolution via improved MTF (modulation transfer function, a measure of lens performance). It also increases telecentricity, making more of the imaging light perpendicular to the sensor. This is difficult to achieve in very wide angle lenses. The result is a reduction in vignetting, which may or may not be visible, depending on the original focal length.

Speed Boosters contain the full set of electronic contacts, which means they support EXIF data transfer, image stabilisation and auto aperture settings as well as partial AF support with lenses released since 2006. According to the Metabones website, other mount combinations to follow shortly include Leica R, ALPA, Contarex, Contax C/Y and Nikon F (with aperture control for G lenses) along with Micro 4/3 and Fuji X-mount cameras. Support for additional mounts will be added in the future.

You can download a White Paper that explains the Speed Booster in detail from