The classic ‘fast fifty’ back only this time with the benefits of modern lens design and manufacturing technologies. Paul Burrows finds that Sigma’s 50mm f1.4 represents a new standard.

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).

There’s no doubt things have come full circle when one of the most interesting developments in current lens design is fast primes. Before zooms dominated the SLR world, the royalty of lenses was anything with a maximum aperture larger than f2.0. F1.8 was good, f1.4 was great and f1.2 was highly desirable.

Twenty or so years ago a 50mm f1.4 was one of the ‘must have’ lenses in any self-respecting 35mm SLR kit. The 50mm focal length – defined as the “standard lens” because it closely approximated the visual characteristics of the human eye – combined with the nicely fast aperture of f1.4 was a much more useful lens than anybody born and bred on zooms probably realises. That it’s back, courtesy of Sigma, is significant for several reasons. Firstly, the demands of imaging onto sensors with totally flat surfaces from corner-to-corner is showing up deficiencies in even the best designed and built zooms. Chromatic aberrations, in particular, are proving a challenge to satisfactorily eliminate at the frame’s edges, particularly in wide-angle 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.

The second reason that prime lenses are making a comeback is the nature of their optical design – chiefly that fewer elements are employed – allows for increased speed without a huge increase in the cost. And, finally, there’s a mystique about the prime lens that’s attracting photographers who want to work within the discipline of a fixed focal length… it’s actually really quite exciting and, of course, now that D-SLRs are delivering much bigger files, there’s always the option of cropping an image later on to refine the framing without losing too much quality.

Prime Time

The ever-alert Sigma has read the signs well. It has offered a selection of f1.8 speed prime wide-angles – 20mm, 24mm and 28mm – for a while and, more recently, introduced a 30mm f1.4 designed for “APS-C” format D-SLRs (which effectively becomes a 45mm f1.4). The new 50mm f1.4 is another DG-series lens; Sigma’s designation for its 35mm format models suitable for either film or digital SLRs.

Appropriately, it’s also an ‘EX’ lens – signified by a thin gold band around the barrel – which is Sigma’s high performance standard so different from our usual diet of zooms – it’s almost square shape being the give-away that it offers great speed via an exceptionally wide diameter front elements. It’s a beautiful looking piece of glass that just begs you to immediately fit a filter of some sort for protection. However, that large diameter front element means the filter fitting is 77 mm.

The optical construction comprises eight elements (in six groups); all glass, of course, and with one moulded aspherical type bringing up the rear to provide correction for various aberrations, notably chromatic and sagittal coma flare. The nine-blade rounded diaphragm produces beautifully smooth out-of- focus effects which, of course, given the inherently shallow depth-of-field at the very large apertures, is important given so much of an image will be blurred to varying extents. Of course, such limited depth-of-field has its advantages in applications such as portraiture or fashion, but it also has great creative potential allied to the use of selective focusing to tell a story.

The contrast between the sharp and the blurred is often overlooked by still photographers as a creative tool, but it’s often used very effectively by cinematographers.