If there's one big problem for Sony's new full-frame mirrorless camera system, it's the lack of native lenses, with just the 35mm, 55m, 28-70 and 24-70mm FE optics currently available.

That has led a lot of early adopters to explore ways of fitting non-Sony lenses to their A7/A7r cameras, which is where companies like Metabones enter the stage with adapters like the Canon EF Lens to Sony NEX Smart Adapter (Mark III) that we're taking a look at today.

This clever product allows Canon EF lenses to be used on the Sony A7 and A7r with full support for electronic aperture and EXIF data, and on some of the more recent EF lenses, auto-focusing and image stabilization too.

We were keen to try out some of our Canon EF lenses on a Sony A7/A7R to find out what the AF performance is actually like and if the combination of the worlds' smallest full-frame camera and a range of Canon optics actually makes sense (or indeed works at all).

The Metabones adapter (MB-EF-E-BM3) fits snugly onto the Sony A7, adding a couple of cms to the depth of the camera. Fitting a lens onto the adapter is an even tighter fit, requiring quite a lot of force to turn the lens into place (this was true of every lens that we tried).

The 5 lenses that successfully autofocused with the Metabones adapter are shown above - the 17-40mm f/4, 24-105mm f/4, 85mm f/1.8, 70-200mm f/4 and the 100mm f/2.8 macro.

We say successfully. Autofocusing the Canon EF lenses on the Sony A7 via the Metabones adapter sounds great in theory, but proved to be a rather frustrating experience. Firstly, it takes at least a couple of seconds for the lens to focus - Metabones themselves say that "Autofocus speed is very slow and inadequate for most moving subjects. The autofocus speed is unfit for professional use for sure, and it would disappoint most enthusiasts." We'd wholeheartedly agree. Furthermore, we often found that the subject was actually out-of-focus, even though the Sony A7 had confirmed the focus point, making autofocusing a slow and unreliable affair.

And here are the 3 lenses that wouldn't autofocus - an older generation Canon EF 50mm f/1.8, Sigma's excellent 35mm f/1.4, and the Tamron 24-75mm f/2.8. Metabones state that "Autofocus is disabled for most third-party lenses."

Don't despair though - manual focusing still works, and best of all, it works really well, so much so that we found it quicker and more accurate to focus manually than to rely on the hit and miss autofocusing. The Sony A7/7R really is a joy to use in this regard, with the combination of excellent focus peaking and a large electronic viewfinder making it a cinch to manually focus.

The 17-40mm f/4 rather dwarves the Sony A7...

...as does the 70-200mm f/4.

In summary, the Metabones adapter successfully allows you to use Canon EF lenses on the excellent Sony A7/A7R mirrorless cameras - just don't expect snappy or reliable autofocusing. Instead, learn to use the Sony A7/A7R's excellent manual focusing system instead, and you can enjoy using Canon's vast range of lenses on our favorite camera of 2013.

Have you used the Metabones adapter with the Sony A7/A7R, or any other adapter? Let us know how you got on in the Comments section below.

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