Sigma’s New 50mm Fast Prime Lens

In an age when many photographers search for one zoom lens to cover all their required focal lengths, Sigma announces an “old fashioned” 50mm prime lens.

Before the advent of zoom lenses, the 50mm primes were the workhorses of SLR photography. They were standard with every camera and were an important part of new camera reviews. Cameras makers put their best foot forward when designing the standard lens, unlike today when the kit lens often suffers from the compromise of achieving a low shelf price for the camera.

Another important aspect of the 50mm design is it gave an approximation of the angle of view of the human eye, so giving a natural look to photographs. With the smaller digital sensors, they now give the view of a 75mm telephoto lens. This is a very good focal length for portraits and general photography.

The Sigma carries their EX designation which they say, “Denotes the superior build and optical quality”, and differentiates it from the price conscious Sigma lenses. Another indication is the large maximum aperture (f1.4), making this a ‘fast” lens. Digital noise from high ISO settings is an issue for DSLRS, and the extra light from the large apertures helps produce low noise images in poor lighting conditions.

The extra light is also an aid to fast autofocus performance and the Sigma incorporates a HSM (Hyper Sonic Motor), ensuring quiet and high-speed AF as well as full-time manual focus override. In a sign of the times, there is no connector to the camera body focus motor. If your camera does not support HSM then only manual focus is available, although most new DSLRs now support HSM. Each manufacturer tends to have a name for it, such as USM and SDM.

The internal construction features a molded aspherical lens, rather than the more traditional manufacturing process of grinding the glass to shape. Aspherical lenses have complex curve shapes to compensate for off axis lens behavior.