Maybe free lunch exists after all. The Metabones Speed Booster is a new adapter for Micro 4/3 and Sony NEX that is designed to reduce the focal length of an adapted SLR lens while increasing
the speed of the lens. This type of adapter, called a focal reducer or telecompressor, is essentially the opposite of a teleconverter.
The idea is not new. For example, the very early Nikon E series DSLR
, co-developed with Fuji, used a 4X focal reducer to get the full angle of view and light collecting power of full frame lenses condensed to a 2/3" sensor, and Kodak has a 1994 patent
describing a device similar to the Metabones Speed Booster.
To date, no one has been able to design a general use focal reducer that will work with fast lenses while effectively addressing optical aberrations, especially spherical aberration and field curvature. According to the white paper
, the engineers behind the Metabones Speed Booster were able to create a focal reducer that accomplishes these goals by designing specifically for mirrorless cameras.
The Metabones Speed Booster reduces the focal length of an adapted lens to 0.71X, where X is the original focal lengh of the lens. At the same time, it increases the lens speed (virtual aperture relative to focal length) by one full stop. Thus a 35mm f/1.4 SLR lens fitted to the Speed Booster physically becomes a 25mm* f/1.0 lens.
*50mm equivalent angle of view on MFT, 38mm equivalent AOV on NEX
For more information, read the white paper: http://www.metabones.com/images/meta...te%20Paper.pdf