Sigma's 50mm prime lens is a "third-party" interchangeable lens option for users of Canon, Nikon, Sony, or Pentax DSLR cameras. It also obviously works on Sigma's own limited range of DSLRs. A 50mm lens is a standard lens on full frame cameras, while converting to a useful 80mm portrait lens on crop frame APS-C cameras. But can it rival other 50mm lenses?
Pros
- Very little vignetting, even at wide apertures on full frame cameras
- Exceptional image quality
Cons
- Heavy and large for a 50mm lens
Autofocus
Sigma's 50mm lens uses its "HyperSonic Motor" (HSM), and it has fast, accurate, and almost silent operation. This is included on all model mounts, and it even provides autofocus for older Nikon DSLR models such as the D40 and D60. Unfortunately, users of older Pentax DSLRs will lose out, only being able to focus manually.
While fast, the Sigma isn't as quick as some of the other manufacturers' own lenses. This is particularly noticeable with Canon's sub-$100 50mm f1.8 lens, which is faster. Accuracy is obviously dependent on light levels, but the Sigma lens copes well in most situations.
Build Quality
The Sigma is an exceptionally well-built lens, with a metal lens mount and a very sturdy plastic body. The front element is deeply recessed, which protects it from stray light, even without using the included lens hood.
However, there's no getting away from the fact that this is a huge lens. It even dwarfs full frame cameras! It's also very heavy for a 50mm lens, and some users may find this a bore to carry around with them.
Optics
Thanks to the oversized lens barrel, the Sigma offers a lens with extremely low vignetting. Chromatic aberration and distortion are minimal, and there's improved sharpness at all apertures. Optically, this really is a superb lens. It's also been designed with APS-C users in mind, and it produces excellent portrait shots.
It's not perfect, of course, and it can't achieve corner-to-corner sharpness on full frame cameras at wide apertures. However, it's unlikely that this will bother users, as, for instance, the depth of field at f1.4 is so small that corner sharpness becomes a null and void issue.
In Conclusion
Optically, this is a spectacular lens, particularly if you're using an APS-C camera, but you want a good portrait lens. Results are excellent. However, there's no getting away from the sheer size of the thing ... and the extra weight you'll need to lug around.
The lens also takes 77mm filters, compared to the 49-58mm threads used with most 50mm lenses. This could increase the overall cost of using the lens significantly, particularly if you want to use things like polarizers.
Overall, though, this is a fantastic lens and, as long as the weight and size don't bother you, I'd recommend you buy one immediately!