Sigma 50mm f/2.8 EX DG Macro - £270/$370
It's hard to resist a 'buy one get one free' offer and, on the face of it, this Sigma is two lenses in one. It's a 50mm prime suitable for both full-frame and APS-C format bodies, and has full 1.0x magnification for macro work. This means that at its closest focus distance, small objects are reproduced life-size on the image sensor.
Ultimately, however, the lens feels like a bit of a compromise. The maximum aperture of f/2.8 is more than a stop slower than that of an f/1.8 lens, and it's more difficult to blur backgrounds. Also, unlike the macro lenses that we featured in last issue's roundup, the fairly short focal length of 50mm puts the front of the lens uncomfortably close to the macro subject you're shooting.
There's also no built-in motor so, as with the Nikon 50mm f/1.8D, the Sigma won't autofocus on entry-level cameras such as the D3100.
This lens is sharp, and distortion is minimal. However, the bokeh effect isn't very impressive and lacks the smoothness you get with the Nikon f/1.8 lenses. Like them, the Sigma uses a seven-blade diaphragm.
You'd expect excellent sharpness from a macro lens, and the Sigma only drops off at apertures of f/22 and smaller.
Sharpness at f/2.8: 1764
Sharpness at f/8: 1865
Sharpness at f/16: 1732
At medium and small apertures, this lens banishes chromatic aberration better than the pricier Sigma 30mm and 50mm.
Fringing at f/2.8: 0.22
Fringing at f/8: 0.25
Fringing at f/16: 0.21
The best on test for distortion, there's the merest hint of a pin-cushion effect but it's practically negligible.
Image test verdict
The Sigma does well in the lab, but the maximum aperture of f/2.8 is limiting and the bokeh effects aren't the most pleasing either.