Sigma EX zoom lens - 10 mm - 20 mm

...Canon and 17-34mm on a Sigma DSLR - not quite the classic 16-35mm range but near enough nonetheless and, a valuable and versatile addition to anyone's APS-C based kit.

This of course is a Sigma DC lens and as such, is suitable only for the APS-C sized cropped sensor DSLR's. It cannot be used on full-frame or 35mm cameras. The EX designation stands for 'Excellence', Sigma's designation for their professional quality lenses and it's ...
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Unlike Canon, Sigma DO include a proper lens hood (petal type), along with a nice soft bag. Bravo Sigma! A hood is essential with such wide angle lenses and it is good to see Sigma leading the way here.

The lens isn't particularly prone to flare which is surprising with it's construction of 14 elements in 10 groups. However, once you see the specification, you will become aware that quite a bit of effort has gone into making ... more

I have owned two of these lenses. One (the first) for my Nikon DSLR (since disposed of) and the second for my Canon APS-C sensor DSLR. Both lenses exhibited near identical characteristics and qualities which does at least imply consistency.

This lens covers the useful range of 15-30mm on a APS-C Nikon, 16-32mm on a APS-C Canon and 17-34mm on a Sigma DSLR - not quite the classic 16-35mm range but near enough nonetheless and, a valuable and versatile addition to anyone's APS-C based kit.

This of course is a Sigma DC lens and as such, is suitable only for the APS-C sized cropped sensor DSLR's. It cannot be used on full-frame or 35mm cameras. The EX designation stands for 'Excellence', Sigma's designation for their professional quality lenses and it's feel and finish are in keeping with this. It is quite weighty (for it's size) although fairly compact and obviously well built, with a nice (I think) smooth black 'crinkle' finish which, while seeming to 'attract' dust, is just as easy to wipe over and keep clean. The lens feels well balanced on most cameras.

With a maximum aperture of f/4 at the widest end and f/5.6 at the longer end, it is a little 'slower' than it's Canon counterpart. However, just like the Canon lens, the technological constraints have not been pushed too hard and consequently, the result is a better performing lens, albeit with slightly less 'exciting' specification. This is no bad thing in my opinion. What's the point of an f/2.8 maximum aperture , when resulting quality is poor, even sometimes at the expense of overall performance throughout the entire zoom range and at all apertures?

Unlike Canon, Sigma DO include a proper lens hood (petal type), along with a nice soft bag. Bravo Sigma! A hood is essential with such wide angle lenses and it is good to see Sigma leading the way here.

The lens isn't particularly prone to flare which is surprising with it's construction of 14 elements in 10 groups. However, once you see the specification, you will become aware that quite a bit of effort has gone into making this lens perform well and with 3 aspherical elements and 3 SLD (Special Low Dispersion) ones, it becomes less of a surprise!

AF focusing is by Sigma's HSM (hypersonic motor) and is very quiet and fast. FTM (Full Time Manual) focusing is available in One Shot AF mode which can be useful. I found the AF to be neither as fast or quite as accurate as Canon's USM system, particularly in dark conditions, but with most subjects this lens will be used for, this shouldn't be a problem. The lens does extend a little towards the long end, although the front element doesn't revolve either when zooming, or focusing, making the use of polariser filters simple. Closest focusing distance is an impressive 0.24m - great for the pebbles into boulders transformations which I'm sure this lens will be put to.

Performance overall is quite impressive, although there 'are' one or two concerns. Distortion being the first. While the lens appears to produce relatively little barrel distortion over most of the field of view at 10mm focal length, quite strong barrel distortion is actually evident right at the 'very' edges of the frame where it can become quite a problem. Certainly, it presents little problem to landscape photographers to whom this lens will no doubt mostly appeal. However, if you like to shoot architecture or interiors, this becomes quite serious. Not only is the barrel distortion pronounced at the extreme edges but there is also an alarming degree of 'stretching' distortion to any objects positioned in the extreme corners of the frame . This is impossible to correct in software. It is here in particular where this lens falls short of the Canon EF-S 10-22mm lens which doesn't exhibit this problem AND has less barrel distortion at the edges. To make matters more complicated, at around 15mm, the lens exhibits quite strong pincushion distortion, although this tends to even out again by 20mm,. These distortion problems are the main reasons why I disposed of my own Sigma 10-20mm lens, replacing it with the Canon 10-22mm.

If you shoot mostly landscapes, this probably won't be too much of an issue - unless you are particularly aware of distortions? ie; Boats, boulders, trees or whatever in the corners of the frame, where it can make things appear just a little 'odd'.

Vignetting is the other problem area. Although expected with such a lens, it is somewhat worse than the Canon equivalent. Vignetting is very obvious at 10mm and f/4 and remains so even at 14mm and f/4.5. It does get a little better at 20mm and f/5.6 but by this time, the best fun is over. Certainly, the problem is helped by stopping down but only to an 'acceptable' level in my opinion.

Resolution or sharpness is really quite good for the price point of this lens, almost equalling the Canon lens in many respects. Even at the widest 10mm end, centre performance is really VERY GOOD although the edges are a little behind at VERY GOOD- while the corners only achieve GOOD levels. Performance is improved by stopping down, when centre performance at 10mm quickly attains an EXCELLENT rating, with edges rising to VERY GOOD and corners to VERY GOOD- which is quite impressive. The lens tends to perform slightly less well from about 14 to 20mm at the edges and in particular, the corners. Although even these retain a satisfactory level.

CA's (Chromatic Aberrations) or colour fringing, are handled quite well by this lens. A little surprising for such a wide angle zoom lens - although not quite as well as the Canon lens, At 10mm focal length CA's are around 1.5 pixels which, although quite noticeable, are still easily corrected in software. The problem decreases considerably when zooming in to longer focal lengths.

This is a really good lens and for most, a good (and less expensive) alternative to manufacturer's own 'marque' lenses. It is particularly good at the widest (10mm) end which is perfect, as this is almost certainly where it will be mostly used. Performance isn't quite so good as you zoom in but this is not what this lens is all about.

Highly recommended - unless you shoot architecture or interiors!

David Chamberlain 

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