Metabones has just announced 0.71x focal reducer lens adapters which they have named “Speed Booster” for a variety of mirrorless cameras including Sony NEX, Olympus and Panasonic Micro Four Thirds, and Fuji-X.

Although expensive at $US599, these adapters will significantly add to the versatility of these camera systems as they will allow:

• high image quality reduction in effective focal length and thus field of view will be closer to that of the native lens field of view – on a 1.5x crop camera such as Sony NEX, the crop factor becomes 1.09x, while on a 2x crop factor Micro Four Thirds camera, the crop factor becomes 1.42x (almost the same as a 1.3x crop APS-H Canon 1D dSLR camera)
• effective aperture for exposure becomes 1 stop brighter, as in effect, more light is squeezed onto the sensor, in other words, it gives you 1 stop higher ISO in effect which can also mean 1 stop less noise
• the Canon EOS adapter will allow aperture change, optical IS, EXIF data, presumably MF-ring activation of magnified view, and, on the post-2006 EF lenses, slow autofocus – an adapter which can do all this at last given that the long awaited Birger Engineering adapter that was meant to achieve these functions has not eventuated.
• and of course, if you use a Olympus camera such as the E-M5, you will get sensor based image stabilisation to any lens – and perhaps you may not even have to dial in the focal length – we shall have to wait and see on this aspect
• the white paper promises excellent correction of spherical aberration as well as field curvature, coma, astigmatism, distortion, and chromatic aberration. Intentionally, it has a very small amount of undercorrected spherical aberration at f/0.90 to improve the bokeh when the Speed Booster is used with ultra high speed f/1.2 objectives. Aberrations should be considerably less than with front-mounted wide adapters.
• being a focal reducer, it increases resolution and contrast (MTF) compared with using the lens without this adapter as it should compress aberrations
• improves telecentricity by moving the exit pupil further away and potentialy could reduce vignetting
• improves image quality of wide aperture legacy film lenses due to improved interaction with low pass and IR filters on the camera sensor, although it appears that image quality may be worse in the corners with some lens combinations such as when using cheap 50mm prime lenses
• physical length is reduced by 6mm on Micro Four Thirds and by 4mm on Sony NEX compared with using a normal adapter

Thus on a Olympus OM-D E-M5 Micro Four Thirds camera, here are some awesome possibilities:

• Sigma 8-16mm DX lens = image stabilised 5.6-11.2mm ultra wide angle zoom lens which is even wider than the Micro Four Thirds 7-14mm lenses but the fixed lens hood may become visible
  
• Canon TS-E 17mm f/4 tilt-shift lens = image stabilised 12mm f/2.8 lens which will give the same field of view and depth of field as a 24mm f/5.6 tilt shift lens on a 35mm full frame camera, but exposure value of an f/2.8 lens image stabilised
  
• Canon EF 24mm f/1.4L II lens = image stabilised 17mm f/1.0 lens which will give the same field of view and depth of field as a 34mm f/2.0 lens on a 35mm full frame camera, but exposure value of an f/1.0 lens image stabilised
• Canon 50mm f/1.2L lens = image stabilised 36mm f/0.85 lens which will give the same field of view and depth fo field as a 72mm f/1.7 lens on a 35mm full frame camera, but exposure value of an f/0.85 lens image stabilised
• Canon 85mm f/1.2 lens = image stabilised 60mm f/0.85 lens which will give the same field of view and depth of field as a 120mm f/1.7 lens on a 35mm full frame camera, but exposure value of an f/0.85 lens image stabilised
• Nikon 85mm f/1.4G II lens or Rokinon 85mm f/1.4 lens = image stabilised 60mm f/1.0 lens which will give the same field of view and depth of field as a 120mm f/2.0 lens on a 35mm full frame camera, but exposure value of an f/1.0 lens image stabilised
• Canon EF 135mm f/2.0L lens = image stabilised 96mm f/1.4 lens which will give the same field of view and depth of field as a 190mm f/2.8 lens on a 35mm full frame camera, but exposure value of an f/1.4 lens image stabilised

The adapter will open up many exciting possibilities, particularly for those who already have full frame lenses.

Adapters will be available for Canon EF/EF-S, Nikon F/G/DX, Leica R, ALPA, Contarex, Contax C/Y , and Olympus OM lenses.

Note that cropped sensor lenses such as EF-S and DX can be used on Micro Four Thirds with this adapter as long as they do not have fixed lens hoods such as the Nikon DX fisheye, or the Sigma 8-16mm zoom, but the image circle is too small for use on Sony NEX size sensors.

Interestingly, I posted in Feb 2010 about a patent by Olympus for a similar type of adapter which would be a 0.5x reducer (2 f stops) for use with Olympus OM lenses, and it was hoped they would be incorporating SWD or contrast detect AF elements as well which would add fast AF to Olympus OM lenses when used on Micro Four Thirds cameras. Unfortunately, this has not seen the light of day, but perhaps this adapter from Metabones may inspire them to produce such an adapter.

See a review of the Metabones adapter by EOSHD from a video perspective here.