Metabones Introduces EF to EOS M (EF-EFM Mount) Speed Booster ULTRA 0.71x


Posted on 05/19/2019 by guidetocamera

Metabones Introduces EF to EOS M (EF-EFM Mount) Speed Booster ULTRA 0.71x

Vancouver, Canada, May 2, 2019 - Metabones introduces the latest member of its award-winning Speed Booster family of DSLR (digital single-lens reflex) to mirrorless lens mount adapters, EF-EOS M Speed Booster ULTRA 0.71x. Full-frame Canon EF-mount lenses are now one stop faster, 0.71x wider and with increased MFT (note 1) on Canon EOS M cameras. The 4k/UHD video crop on EOS M50 can also be mitigated with third-party APS-C lenses using this Metabones Speed Booster. Some Canon EF-S lenses may be modified to fit on the Speed Booster but Metabones cannot be held liable for any issues arising from modifications. Using APS-C lenses with Speed Booster for still photography or full HD videography may result in vignetting.

Ever since the first Speed Booster was introduced, there have been DIY attempts to modify it to fit EOS M cameras. The turnkey solution Metabones now offers adds a number of refinements:

The optical housing is redesigned for perfect fit on EOS M.

The EXIF metadata is changed to reflect the faster aperture (note 2) and shorter focal length.

 The autofocus speed of the lens is adjusted and optimized for the change in focal length and aperture to ensure the best performance. This is especially important for dual-pixel autofocus (DPAF) in video mode.

A 'chip' mode is added so that the user may store the metadata of a fully mechanical manual lens in the adapter.

A LED indicates operational status of the Speed Booster.

Since both the lens and the camera speak the same protocol most features are supported with the exception of lens aberration correction, which is automatically turned off.

Speed Booster ULTRA

Speed Booster ULTRA uses an advanced 5-element/4-group optical design by Caldwell Photographic Inc., incorporating ultra-high index tantalum-based optical glass to achieve extraordinary optical performance with improved corner sharpness, distortion and reduced vignetting. Speed Booster ULTRA has a magnification of 0.71x, effectively reducing the crop factor of APS-C cameras from 1.5x to 1.07x. The Speed Booster ULTRA design makes very effective use of exotic materials at the furthest limit of glassmaking technology, and as a result is well corrected for use with virtually all full-frame SLR lenses regardless of exit pupil distance. Thus, the Speed Booster ULTRA performs extremely well with professional-grade f/2.8 zoom lenses such as the 24-70mm f/2.8 and 70-200mm f/2.8 zooms by Canon to produce 17-50mm f/2.0 and 50-142mm f/2.0 high-speed zooms, respectively. Similarly, high-speed fixed focal length lenses such as a 50mm f/1.2 will be transformed into a 35.5mm f/0.9 lens with excellent contrast and resolution from the center all the way to the edges of the image.


Metabones EF-EOS M Speed Booster ULTRA 0.71x is available right now for USD 479.00 plus applicable taxes, duties and shipping, from Metabones' web store and its worldwide network of resellers.

Note 1: compared to the same lens on the same camera with an ordinary lens mount adapter without optics.

Note 2: to ensure compatibility with hardware and software, which do not always handle sub-1.0 apertures properly, f/1.2 lenses will display their pre-boost aperture. Please rest assured that the display has no impact on the actual maximum aperture and a maximum output of f/0.9 is supported.  


  • Product name (Model Code):
  • Canon EF Lens to EOS M (EF-EFM Mount) T Speed Booster ULTRA 0.71x (MB_SPEF-EFM-BT1)
  • Dimension: 27.1 x 72.3 x 76.0mm
  • Product Page :
  • Weight: 192g
  • Retail Price: USD 479.00
  • Color: Black Satin exterior; Black Matte interior