The rise of full-frame mirrorless cameras, such as the Sony A series, has seen a commensurate explosion in the use of third party manual focus lenses via an adaptor on the camera.

So it was with some excitement that I learned about a new, world-first product called the Tech Art Pro that coupled the excellent selection of Leica M-mount lenses to a Sony E-mount and enabled auto-focus. That's right, auto-focus on a manual lens.

The excitement grew when I discovered that the adaptor would only set you back $515 , which, if you think about it, isn't that much. The cost of a new digital Leica is near the $10,000 mark. A feature-filled Sony A7II is perhaps a quarter of that, plus, with the purchase of this adaptor, you would get auto-focus!

Unfortunately the idea, though brilliant, has glaring issues that make it a hard decision to justify.

The Tech Art Pro uses a motor and variable extension tube to move the lens backwards and forwards, enabling focus through Sony's phased detection system. The auto-focus works quite quickly and responsively in everyday situations and is not loud, but throw the unit in complex light and it struggles.

First up, the design issues. The Tech Art Pro's small motor, which sits underneath the adaptor, gets in the way of the camera's tripod mount because it extends past the bottom housing of the camera. For some small tripods that won't be a problem, but for many it will. The company offers an additional L-bracket that fixes the issue, but it costs extra. It should probably come as standard.

The M-mount part of the adaptor does not feel particularly well made, although every other aspect of the unit does. I had issues mounting M-lenses, and it felt scratchy and put up a lot of resistance, unlike my experience with manual-only adaptors from brands such as Novoflex or Fotodiox.

The Tech Art Pro in use also raises serious problems. Auto-focus drains the camera's battery, and seemed to do so even when the unit was turned off. I've heard that taking the battery out of your camera when the unit is attached and the camera is off solves this problem, but you shouldn't have to do that.

The image quality, when compared to a native Leica digital camera, is inferior in terms of sharpness. I compared the Tech Art Pro on an A7II directly against the 2009 Leica M9. The M9 produced sharper images using manual focus at wider apertures, than the A7II with this adaptor using auto-focus. The lens tested was a Carl Zeiss 28 F2.8 ZM. The issues was not lens based, I got similar results from a Carl Zeiss 35 F2 ZM and a Leica Summilux 50 F1.4.

The entire point of using some Leica M-mount lenses is to take advantage of their excellent image quality capabilities, so it seems self-defeating to get inferior results on the Sony A7II, which has better technology than the Leica M9.

That said, the adaptor is a lot of fun and still represents a great gimmick if you have to have auto-focus for your Leica lenses. It was fantastic to use when walking around in well-lit situations, but you are making compromises. Even with the issues raised here, there is a real place in the market for an adaptor that does what this unit does – as most of us can't afford a digital Leica . If the company irons out the design flaws with a second version, this will be an excellent product.