You know all is well with the world when you can again buy the traditional ‘fast fifty’ although Sigma’s revival of a classic design is packed with the latest technology. Report by Paul Burrows.

In this era of ever more exotic zooms, it’s something of a surprise to find that the classic prime lens is making a comeback. Ironically, it’s the very particular demands of digital capture that is the driving force… as it is with the return of the hand-held exposure meters and even the colour temperature meter. The particular challenges of imaging onto sensors with micron-flat surfaces from corner-to corner is showing up deficiencies in even the best designed and built zooms. Chromatic aberrations, in particular, are a proving a challenge to satisfactorily eliminate at the frame’s edges, particularly in wideangle zooms. Maintaining uniform centre-to-centre sharpness and brightness is also more difficult in a zoom despite the swag of new optical technologies now being employed. The same is true of distortion which becomes especially problematic as the zooming range increases. So – as was always the case – a good prime lens will beat a good zoom lens in terms of optical performance any day.

Sigma recognised this some time ago with its first DG-series primes, the f1.8-speed 20mm, 24mm and 28mm wide-angles. ‘DG’ is Sigma’s designation for digital lenses that are designed for use with 35mm format D-SLRs, but can obviously also be fitted to the smaller format bodies (with an increase in the effective focal length). Next came a DC-series lens, the 30mm f1.4 designed specifically for the “APS-C” format (which actually becomes a 45mm f1.4 with a focal length magnification of 1.5x). Now comes arguably the most interesting Sigma prime lens yet in the shape of a DG-series 50mm f1.4. It’s interesting not just because it’s a ‘fast fifty’ which was once the most important lens in any 35mm SLR kit, but because it’s a design that can really show off a lens maker’s capabilities. So, in many ways then, Sigma is making a definite statement with its 50mm f1.4… most specifically about its capacity to deliver a very high level of optical performance indeed.

Taking The Challenge

Of course, the 50mm prime was the original standard lens, defined as such because this focal length – on the 35mm format – closely approximates the visual characteristics of the human eye.

Combined with a fast aperture of f1.4, it represents a lens that’s a lot more versatile than anybody born and bred on zooms probably realises. However, the performance challenges remain the same as they did in the 35mm era except that they’re now somewhat greater when it comes to digital capture onto imaging sensors.

Despite all the recent technologies that have helped improve the performance of zoom lenses (aspherical elements, glass moulding, extra-low dispersion glass, etc), the rules of optics and physics still mean that having fewer elements in an optical design equates to having fewer problems that require correction. This, as ever, remains the key advantage that a prime lens has over a zoom. That said, Sigma has still incorporated the latest lens technologies into its ‘fast fifty’ in the quest for the highest possible levels of correction.

Appropriately, the 50mm f1.4 is an ‘EX’ lens – signified by a thin gold band around the barrel – which is Sigma’s high performance standard in terms of both the mechanical and optical constructions. Sigma’s EX lenses also have an attractive matte anodised finish which the 50mm f1.4 wears particularly well. It truly is a great looking lens – perhaps because it’s so different from the usual diet of zooms – but the big surprise is its size. It’s significantly bigger than Canon’s 50mm f1.4 USM EF lens which has been pretty much the benchmark in terms of digital fast fifties.

Sigma’s DG-series 50mm f1.4 is designed for use with 35mm format film and digital SLRs, but it can also be used on “APS-C” format D-SLRs. The effective focal length then becomes either 75mm (at 1.5x) or 80mm (at 1.6x).
The Sigma 50mm f1.4 delivers exceptional optical performance in terms of sharpness, contrast, brightness and high levels of correction for both distortion and chromatic aberrations. In fact, there’s no noticeable distortion at all.