Given that Sigma lenses have such a strong presence in the d-SLR market it seems only fitting that Sigma has become the first independent lens manufacturer to expand into the Compact System Camera sector as well.

Two prime lenses have been launched and to a casual glance it is hard to tell them apart. The 30mm lens reviewed here is actually slightly shorter, physically, than its 19mm stable-mate but the difference is only a matter of a few millimetres.

Picking-up the Sigma 30mm f/2.8 EX DN can be a little disconcerting as it appears to rattle. The instruction sheet acknowledges this, noting: the lens may emit a chattering noise but this is not a malfunction. The same noise can be heard when the lens is attached to a camera body if the camera is not powered-up.

This is not surprising because there are no mechanical contacts between the camera and lens, so almost all controls and functions are subject to electrical power.

The exception is manual focusing, which is conducted by rotating the broad ring that occupies the front half of the lens barrel. Sadly, the focusing ring on the review lens was stiff and jerky almost to the point of being unusable given the insecure grip that has to be adopted when using any non-viewfinder camera body. (The review was carried out using an Olympus PEN Mini.)

Fortunately, automatic focusing is both very quick and very quiet: in fact it is virtually silent. There is no in-lens image stabilisation but the Olympus body offers this feature. Similarly, switching between AF and MF is achieved by changing a software setting rather than by flicking a mechanical switch. And there are no facilities on the lens to indicate either the focussed distance or the limits of depth-of-field.

None of that may matter to some devoted users of Compact System Cameras but everybody will be keen to hear about the 30mm’s lens sharpness figures.

The good news is that Sigma 30mm DN-format prime is a very strong performer indeed. Its MTF curve is comfortably above the critical 0.25 cycles-per-pixel level for all aperture settings except f/22. Some signs of chromatic aberration were seen on high-contrast test targets but not within real-world photographs.