Cut the Crop: A Hands-On Review of the Metabones Speed Booster ULTRA

December 11, 2015

By Josh Root

With compact sizes, large lens systems, affordable prices and resolution up to 4K, mirrorless cameras, particularly Micro Four Thirds, have found their place in filmmakers’ bags. One drawback of these small sensor cameras has always been their inability to offer shallow depth of field for a given field of view. 

What if there was a product that would allow you to put your full-frame DSLR lenses on a Micro Four Thirds body with full electronic control and autofocus? Not only that, but this device would reduce the focal length conversion (a.k.a. the “crop factor”) of your body by a factor of 0.71x, retain the shallow depth of field and give you a full extra stop of lens speed. That is exactly what the $649 Metabones Speed Booster ULTRA 0.71x is able to do. 

The EF-MFT mount T Speed Booster Ultra 0.71x. 

The best way to think about the Speed Booster is as an inverse teleconverter. Teleconverters magnify the central portion of an image circle to cover the sensor. You lose a stop or more of lens speed because with only a section of the image circle falling on the sensor, only a portion of the lens’s light gathering ability is being used. The Speed Booster takes an already oversized image circle, one intended for the 35mm sensor size, and concentrates it down to cover the Micro Four Thirds sensor. The lens, however, is gathering the same amount of light. Since it is falling on a smaller area, it is brighter, thus accounting for the extra stop of lens speed. The de-magnification needed to reduce the image circle’s size is what accounts for the focal length difference—again, the opposite of how a teleconverter works. 

As a practical example, let’s take a standard 50mm f/1.4 lens. Ignoring lens mounts and just thinking about the optics, on a Micro Four Thirds camera, a 50mm lens would have the same field of view as a 100mm lens on a full-frame camera. Using a 50mm lens on your MFT camera with the Metabones Speed Booster ULTRA 0.71x would give you a 35.5mm lens to start with (50 x 0.71 = 35.5) and an equivalent field of view of a 70mm lens. This is very similar to the crop factor that APS-C or Super 35mm cameras provide. Additionally, the increased brightness of the image circle would move the maximum aperture from f/1.4 to a Leica Noctilux-esque f/1. 

Image Quality

Metabones claims that the glass element in the Speed Booster is so well designed, and of such high quality, that it can actually improve the MTF (modulation transfer function) performance of lenses it is used with.  

There are two ways to look at this. Standard wisdom says that anything you put between your lens and the sensor will degrade the image quality. Designed correctly, however, extra elements can correct for optical weaknesses in lens design. In real world testing, I can confidentially say that the Speed Booster does not degrade image quality, and may, in fact, increase sharpness. More recently designed lenses seemed to fare better than some older film-era designs. In my testing of a limited assortment of lenses, however, none fared badly. 


The Speed Booster ULTRA 0.71x looks, at first glance, very much like a teleconverter. It is a small unit, about the size and thickness of a pancake lens, that sits between the Micro Four Thirds body and your Canon EF lens. 

Not all Canon EF mount lenses can be used with the Speed Booster. Specifically, EF-S lenses protrude too far into the mount and would touch the Speed Booster’s glass element. Third party APS-C sensor lenses, however, do not have this issue, as they use the standard EF mount. There’s a detachable tripod foot as well.

A recent firmware update adds autofocus to Olympus camera bodies.

What We Liked

For long-time photographers and filmmakers, the Speed Booster ULTRA 0.71x feels a little like magic. Many of us have used so called non-electronic “dumb” lens adapters at different times. Little more than extension tubes, these were frustrating to deal with, had no electronic control and gave no optical advantage. The Speed Booster on the other hand, communicates smoothly between the lens and body. In terms of settings and control, there is no difference between using a Speed Booster with an EF lens and a native Micro Four Thirds lens. 

Most importantly, the Speed Booster does exactly what it was designed for. It gives you the ability to have a shallower depth of field and an extra stop of light when filming with Micro Four Thirds lenses. The Speed Booster does the job it was designed to do and does it well.

What We Didn’t Like

Autofocus should be viewed as a partial bonus when using the Speed Booster rather than a full feature. It works, but Metabones makes no secret of the fact that it has some limitations. It will only work with a specific set of lenses, and is not at all comparable to native lens AF performance. 

When introduced, the Metabones Speed Booster ULTRA 0.71x offered autofocus with Panasonic bodies. A recent firmware update, which was very easy to apply, added autofocus for Olympus as well. But Olympus cannot use AF while filming and neither can use C-AF or Tracking-AF. Single AF works, particularly for still photos, but it stutters and is slow compared to native lenses. It is, however, fairly accurate within these limitations. That shouldn’t be a big deal for most serious professionals though, as few trust autofocus for filmmaking.

How It Compares

There are precious few competitors to the Speed Booster on the market. Most of what is available are either “dumb” adapters with no electronic control or Speed Booster knock-offs of wildly varying quality. If you are a mirrorless filmmaker who has access to full-frame lenses, there is almost no reason why you wouldn’t want to get your hands on a Speed Booster. It is one of those rare products that lives up to virtually all of its hype. 

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