Autofocus Converted Contax N Test: 17-35mm f2.8

Contax N 17-35mm f2.8 v Nikon AFS 17-35mm f2.8

Introduction | Skip the blurb: show me the pictures >

For many years Canon users have sought out Zeiss and Leica lenses for optimal full frame performance. They've bought, sanded down, measured and modified adaptors; they've hacked bits out of their cameras and dremelled bits off their lenses and even poked incompatible (and unfeasible) lens barrels into their digital bodies, and all the while tolerated manual focus, manual aperture control, and unreliable metering – all in the name of a little extra magic and sparkle.

Casting about for pastures new, they looked enviously over the fence into the Contax N paddock, where nine exotic creatures of the finest pedigree have been retired before outgrowing their youth: a new breed of full frame Zeiss lenses, designed for digital, T* coated – autofocus, even – but off limits. No matter how tantalising the similarity between the N's autofocus and Canon's USM, or how close the mounts may be in physical size, adapting the lenses for EF just isn't possible: the similarity in size is half the problem. Some speculated: if only the electronics could be persuaded to talk the same language – surely the mount could be replaced? But mostly it was just talk: the idea of using autofocus Zeiss lenses on a 1Ds II or 5D remained a pipe dream . . . until late 2006.

Deciphering the communication protocols and solving the mechanical issues raised by the prospect of such a conversion took Bo-Ming Tong of Vancouver-based Conurus more than a year, but by the winter, he was turning around Mark II conversions of 24-85mm Contax N lenses to the delight of a small number of Canon users. When used on a 1Ds II, the lenses work just like a Canon L: auto focus, auto aperture, and all the Zeiss mojo you can shake a stick at.

Among Contax users, the 85mm 1.4, 100mm Makro Sonnar and 17-35mm f2.8 have acquired legendary reputations. The 17-35/2.8 in particular is a fearsome beast: almost a kilogram in weight and taking a 95mm filter thread. But it was widely considered by those who used them, such as Irakly Shanidze of Luminous Landscape, to be the finest of its kind. As soon as the conversion became available, I was as close to the front of the queue as possible.

The conversion requires a few modestly priced donor components from Sigma, and the price varies somewhat from lens to lens, but what arrived back from Canada after a few weeks was a beautifully converted lens that slotted onto a Canon body and just worked. The standard of the finishing was superb, and there were no electronics gremlins to report: it just worked. The lens itself has a presence and build quality that is almost unequalled. There appear to be no controls on the lens bar aperture and zoom, but Contax N users (apparently) know that manual focus mode is accessed by setting the lens to f22. I didn't, until I was clued in by a promptly returned email from Conurus.

Assuming it was safe to compare the lens using Zeiss' own data, comparing the zoom to better attested primes in Contax/Yashica mounts, here are some comparisons. First, the Contax N 17-35mm at 17mm compared with the older Distagon 18mm:

On average, then, we might expect the zoom to match or outperform the prime, but there is a curious irregularity about the N's MTF data: from the outset we should be mindful of the fact that this is a lens designed for a 6MP full frame sensor: a pretty easy gig compared with a 1Ds II. Here is Zeiss' data comparing the 25mm Distagon with the zoom at 24mm:

Finally, at the maximum extent of its reach, here's the N zoom compared to the superb little 35mm f2.8 Distagon . . .

So it'll not replace your favourite 35mm prime, then. Part I of this review will demonstrate what these squiggles look like in real life shooting conditions in the 17mm to 21mm range. Part II will look at 24mm and 35mm. Naturally, its logical competitor here is the Nikon 17-35mm f2.8 AFS zoom which has acquitted itself superbly against all comers thus far. We will also be featuring a different sample of the same lens compared with the Zeiss 21mm, Zeiss 15mm and Canon 16-35mm L next week, thanks to the efforts of Andrew Gough, who flew to Vancouver to collect the very first converted N 17-35mm ever sold. Page update pending.