"Sony's NEX cameras have a great deal going for them, especially the NEX-5n which is turning out to be one of the most popular new cameras of Q4 2011. But the widest E mount lenses available are 16mm, which on an APS-C sensor is the equivalent of 24mm. This is wide, but in many situations, not wide enough.
Fortunately NEX cameras have such a short lens-flange-to-sensor distance that virtually any lens ever made can be attached. Regular readers will know that I am something of a Leicaphile, and have a good collection of Leica M lenses. I also have a Sony A900 is my primary DSLR, and a full selection of Sony / Zeiss lenses. Since the new LA-EA2 adaptor allows any Sony Alpha mount lens to be attached while using phase detection autofocus, there is a wealth of really wide lenses available.
For this test I decided to look at two of the widest lenses available – the Cosina Voigtländer Ultra Wide-Heliar 12mm f/5.6 and the Sigma 8-16mm f/4.5-5.6 DC HSM. The Voigtländer is one of the widest rectalinear full frame lenses available, while the Sigma is the widest APS-C format lens focal length available. On a NEX-5n the Voigtländer becomes equivalent to an 18mm, while the Sigma at its widest focal length becomes equivalent to 12mm.
The 12mm Voigtländer sells for about $850, with an M to NEX adaptor costing an additional $50 to $250. The Sigma costs about $700 at retail, while the LA-EA2 adaptor costs another $400, for a total of $1,110. This makes them quite similar in price. The Sigma on the LA-EA2 is quite a bit larger and heavier, but has autofocus. The Voigtlander is more petite, but is manual focus only, and not a zoom.
The availability of autofocus may seem like a significant advantage for the Sigma, but in reality isn't so much. Lenses this wide have considerable depth of field at typical shooting distances, and so zone focusing is usually all it takes. More on this shortly.
Lets see how they each perform on the NEX-5n and how they compare with each other..."