Andy Westlake tests a mount adapter that promises to autofocus any lens on the Sony Alpha 7 II and Alpha 7R II full-frame mirrorless cameras
Techart PRO Leica M – Sony E autofocus adapter review: Performance
Of course the big question with such a device is whether it actually works? To find out, I tested it with lenses ranging from an Olympus OM 24mm f/2.8 wideangle to a Tamron SP 500mm f/8 mirror lens. In short, yes it works – although with some limitations.
Most importantly, its 4.5mm focusing travel is only really sufficient for lenses of around 50mm or wider; with longer telephotos the range of AF adjustment using the adapter alone becomes very limited. For instance, with a 135mm lens the adapter only allows focusing as close as 4.2m, when the lens itself is set to infinity. But that’s not necessarily a complete disaster; you can still focus the lens manually to approximate the correct distance and then use the autofocus to fine-tune. It’s not like using a proper AF lens, but it works.
Autofocus is unexpectedly fast; indeed with small lenses it felt more responsive than some of Sony’s own budget primes such as the FE 50mm f/1.8. Focusing slows down in low light, but that’s only to be expected. The set aperture also has an effect on autofocus, because M-mount lenses stop the diaphragm down directly as the aperture ring is turned, and most mount adapters for mirrorless cameras force the lens to work in the same way.
But while most DSLRs can’t autofocus at effective apertures smaller than f/6.3 or thereabouts, I found that on the Alpha 7 II autofocus continues to work pretty well when the lens is stopped down as far as f/11. Indeed the camera was quite happy autofocusing my 500mm f/8 mirror lens, which is some achievement. But if you wish to use even smaller apertures such as f/16 – still a perfectly sensible working aperture on full frame – it will stop functioning reliably.
Focusing isn’t entirely silent; instead the adapter’s built-in motor buzzes away quietly to itself, especially if the camera is hunting for focus. To be fair, it’s not hugely obtrusive, but we’ve become so used to near-silent focusing on modern CSC lenses that it still stands out quite noticeably. Then again, in situations when you need quiet operation, you can simply revert to manual focus. Disconcertingly this option is greyed out in the camera’s menus, but it can still be engaged by configuring the AF/MF button on the camera’s back to its ‘toggle’ setting.
Continuous autofocus is supported for stills shooting, and while this works, don’t expect miracles. It’s not going to be the tool of choice for fast-moving subjects like sports and wildlife, but for portraits where the subject is moving relatively slowly, it should be able to keep up just fine. In video mode, however, continuous AF has sensibly been disabled.
One notable strong point of the Techart PRO adapter is its autofocus accuracy. Because it’s working with the camera’s on-chip phase detection rather than using a separate light path, it’s inherently accurate and not subject to the kind of systematic front or back focus problems that can plague DSLRs. I found it even worked pretty reliably with my Olympus OM 55mm f/1.2, a lens that’s decidedly hazy wide open due to high levels of spherical aberration, and usually quite difficult to focus. The AF point can also be moved around the central area of the frame to some degree, although not to anywhere near the same extent as with contrast-detection lenses.
One useful property of this adapter involves close focusing. If you set the lens to its usual minimum distance, it’s possible to focus even closer by adding in the adapter’s movements – in effect like adding a short extension tube. With a standard 50mm prime, this can buy a few useful extra inches of close-up ability.
On a related note, it’s also important to appreciate the possible impact of using the adapter on close-up shots. Most old lenses employed unit focus designs, moving the entire optical unit back and forth to focus. In such cases, the adapter is essentially doing the same thing, so there’s no negative impact on image quality. But some lens designs use a floating focus system to give better image quality at close distances, and in this case it’s better to use the lens’s own manual focusing mechanism.