An adapter to make lenses wider and better

Metabones is one of a number of companies that specialize in making adapters so that you can use lenses designed for one type of camera on another.  The growing popularity of mirrorless systems, particularly among videographers, has meant that there are now a great many cameras out there that can be made to physically accept lenses built for other cameras.  In late November, Metabones got a good amount of attention when they announced that they’d built an adapter that would let Canon lenses function more or less fully on Sony’s NEX mirrorless cameras – include features such as image stabilization and autofocus.

This week, Metabones had something even grander to show off – the ‘Speed Booster’ adapter that purports to make lenses faster, wider and even in some respects sharper.

The basics of the new adapter are fairly straightforward.  It behaves essentially like a reversed magnifying glass – concentrating the image projected by the lens into a smaller area.  The result is that it decreases the focal length of the lens by a factor of 0.71x, and increases the brightness, which is to say the max. f-stop, by nearly one stop.

Say for instance that you have a 50mm f1.8 lens capable of covering a full frame digital sensor (24x36mm).  Put it in front of the new Metabones focal reducer, and you suddenly have a 35mm f1.3 lens projecting an image that only covers a 16x24mm area, the size of an APS-C sensor.

Before the arrival of mirrorless cameras, this sort of design would have been extremely difficult, as the lens elements in the adapter would in most cases have blocked the flipping reflex mirror.  Thanks to the loss of the mirror and the new shorter lens mount distances on many current cameras, there’s now plenty of space to fit those elements.

The great benefit of all this is that for APS-C sized sensors, the adapter more or less negates the crop factor.  Thus the 50mm lens when mounted on an APS-C camera with the adapter has an angle-of-view very close to what that 50mm lens would have on a full frame digital.  Considering the large numbers of lenses designed for the larger format and the comparatively much smaller number of fast lenses designed for the new mirrorless cameras, that’s quite an advantage.

For a detailed examination of the implications of this new focal reducer adapter, take a look at the whitepaper hosted by Metabones.

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