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The 20-40mm f/2.8 EX lens is a new addition to the Sigma range. Providing a continuous maximum aperture of f/2.8 between the minimum and maximum focal lengths. It has a minimum focusing distance of 30cm throughout the range and the maximum magnification ratio is 1:4.6.
The Sigma 20-40 is quite bulky in the hands
The lens incorporates aspherical lenses in both the front and rear groups, which Sigma claim will minimise distortion and spherical aberration, features common when using wide-angle lenses. AF and MF are options provided by pushing the focusing ring forward for AF and towards the camera for manual. An inner focus (IF) system makes it easy to hold the lens, as the focusing ring does not rotate during autofocus. In addition to this, the IF system provides adequate dampening of the focusing ring in the manual focus mode. This gives it a continued smooth action, common to both focusing settings.
The lens' focusing ring pushes and pulls to change focusing mode
Generally the lens is a joy to use. Focusing is quick and precise, even in low light conditions and a smooth and quiet action make it all the better. The lens has good build quality and feels solid in the hand.
Weighing in at 595g, the Sigma compares favourably to camera brand lenses. Nikkor's 17-35mm f/2.8, for example, is the heaviest at 745g, while other big brand names tend to be, on the whole, slightly heavier than the Sigma. The one notable exception is the Canon 17-35mm f/2.8 USM, weighing just 545g, but it costs approx. 1550.
The Sigma lens falls into a category on its own. You have on one extreme the pro lenses from the likes of Canon and Nikon costing two to three times as much and the enthusiast lenses from Cosina and Tokina at over half the price. This puts the Sigma in a difficult but unique position. It offers professionals a budget option that they will be thinking can it stack up and amateurs who are wondering if the price hike can be justified.
The filter thread is a huge 82mm - use a system such as Lee or Cokin X if you want to save on filter costs.
There's no doubt that image quality is slightly better from the camera manufacturers own brand pro spec lenses, but only marginally, and definitely not enough to justify paying twice as much for a lens, so this new offering from Sigma should be given serious consideration by the professional. Enthusiasts have to weigh up the pros and cons. Cost is the con but points to consider in spending 650 on a lens include the fact it has a continuous maximum aperture of f/2.8. On lower pitched lenses, such as the new Tokina 19-35mm, this reduces down to a variable f/3.5 - f/4.5 depending on focal length. To get round this you could shoot on faster film but you'll have grainier results and the viewfinder image won't be as bright. If you're a bright light shooter neither of these problems will bother you.
The lens comes with a heavy duty pouch and a petal lens hood shown here
Distortion and aberration tends to be a fact of photographic life when using zooms, especially wide-angles like this, but these flaws have been reduced with the optical design of the Sigma lens.
The 20-40mm focal length range is ideal for landscape photography as well as architecture and group shots
The closest focusing distance of the Sigma 20-40mm is about 30cm
Detail is good right into the edges as displayed here with this image shot on Jessop Pan 100
If you can justify the expense for the features that the Sigma lens provides it will deliver the goods and is a perfect alternative to the high priced manufacturers' own brand options. If you shoot in bright conditions and the lens is more for fun use than professional, you would be better looking at the Tokina 19-35mm as a low cost alternative.
Test by Heather Powell