Canon Mount Adapter EF-EOS R 0.71x

The Canon Mount Adapter EF-EOS R 0.71x is an optical speed-booster-style adapter, Canon’s own in-house version of this design, built specifically to let Canon EF-mount lenses be used on Canon’s RF-mount Super 35mm cinema cameras, most notably the EOS C70. Rather than functioning as a simple mechanical pass-through, it contains internal optics that convert light transmission from full-frame to the Super 35mm image format, letting a full-frame EF lens retain an angle of view close to what it would produce on a full-frame body, rather than suffering the usual crop-factor narrowing that comes from mounting a full-frame lens on a smaller Super 35mm sensor.

The adapter’s internal optical element reduces the effective focal length by a factor of 0.71x, compensating for the Super 35mm sensor’s crop and restoring a wider, more full-frame-like field of view. For example, a 24mm EF lens effectively behaves close to its original 24mm angle of view on the C70’s Super 35mm sensor, rather than appearing considerably longer. As a byproduct of this optical design, the adapter also increases light transmission by one full stop, boosting the effective maximum aperture of the attached lens, which is particularly useful in darker shooting conditions.

Full electronic communication is maintained through integrated contacts, supporting Dual Pixel CMOS AF, automatic exposure (AE) and Auto Iris control, lens metadata transmission (including accurate f-stop and focal length display), and in-camera correction for vignetting and lateral chromatic aberration on compatible EF lenses, functioning much like a native EF-mount connection.

Build quality includes a secure four-screw locking collar, in addition to the standard RF-mount flanges, for a robust physical connection specifically designed around the EOS C70’s mount. Canon states the adapter is weather-sealed, though only when properly mounted to the C70, and the company has confirmed the adapter is designed and intended for use with the EOS C70 rather than other RF-mount bodies.

Key Features
– Optical speed-booster-style adapter for Canon EF lenses on RF-mount Super 35mm cameras (designed for the EOS C70)
– 0.71x optical focal length reduction, restoring a full-frame-like angle of view on Super 35mm sensors
– Increases maximum aperture by one full stop
– Full electronic communication: Dual Pixel CMOS AF, AE/Auto Iris, lens metadata
– In-camera vignette and lateral chromatic aberration correction (compatible EF lenses)
– Four-screw locking collar plus RF-mount flanges for secure attachment
– Weather-sealed when mounted to the EOS C70
– Designed and intended specifically for use with the Canon EOS C70