Sigma 18-50 f/2.8 EX DC Interchangeable Lens Review

This is Sigma’s EX version of what is fast becoming a standard lens for digital SLRs with a cropped sensor. The lens carries the DC classification, signifying that it will only work on cameras with the smaller sensors. Sigma already produces a budget f/3.5-5.6 version of this lens’ focal length, so why have they tooled this lens, and is it worth the extra? We put it through our test program to find out.

Specification

• Focal length: 18-50mm
• Angle of view: 69.3-27.9°
• Aperture: f/2.8
• Filter size: 72mm
• Construction: 15 elements/13groups
• Focusing: Internal
• Closest focus: 20cm
• Weight: 450g
• Size: 79x85.8mm
• Mounts available: (AF) Sigma, Canon, Nikon, Pentax, Minolta, 4/3rds
• Price: £370

Build and handling
Being an EX designated lens, opening the box reveals the documentation includes a two year extended UK warranty, giving three years in all. The lens is packed in a padded pouch that is well made and, at last, Sigma has added a belt loop on the back. This actually makes the pouch useful!
The finish is the regular matt black of all EX lenses which is smart and easy to wipe clean, as well as being hard wearing.

Sigma’s well proven AF/Manual focus switch is located in the usual place, left side of the barrel just in front of the mount. Above, and in front of this, is a zoom lock that locks the lens at 18mm, but I found this completely redundant as the mechanism was so well torqued that it did not creep, but was still easy to adjust. The zoom ring is marked at 18, 24, 28, 35 and 50mm and occupies 2/3rds of the barrel, ample wide enough for even the biggest of hands. It's mainly covered in a large pattern ribbed rubber surface.

The remaining third of the barrel is taken up by the focus ring, which has a smaller pattern ribbing and a basic distance scale in metres and feet.

The front element, which extends some 21mm on zooming to the 50mm focal length, does not rotate during use, helpful when using filters.

Focusing is fast. In fact it is almost instant, one of the advantages of the large aperture of this lens. Despite using it in some very low light situations the lens never once hunted, picking up the focus first time, every time.

The supplied petal hood is a bayonet fit that is reversible for storage, and does its job well with no signs of vignetting.

Optical quality This is where this lens really proves its worth! It's outstanding and the sharpest lens I have tested to date, which includes some top glass from leading camera manufacturers. Chromatic aberration is very well controlled, although at the wide-open aperture of f/2.8 there is some evidence in the corners of the pictures. This disappears as soon as the lens is stopped down by half a stop. It is, however, evident at all focal lengths. Once down that half stop, this lens goes way past average with even the edge performance being good and the resolution achieved in the centre of the lens being outstanding. The figures for the lens at f/5.6 at 28mm being the highest achieved on any lens I have tested to date. The colour rendition is neutral, as is the norm with Sigma lenses and the contrast excellent. Distortion is also well controlled for a lens of this type, with very slight barrel at the wide end turning to slight pincushion at the long end. However, you need to photograph geometric shapes at the edges of the frame to notice it! I encountered no flare or ghosting while using this lens, which included shooting straight into the setting sun.	Steam Crane, Bristol Docks. 1/80sec at f/22 18mm
Clifton Suspension Bridge, 18mm, f/6.3 at 1/400sec. Henbury’ shunting engine. 1/100sec at f/8 21mm
	The ‘Matthew’ at Bristol . 1/400sec at f/8 50mm

18-50mm at 18mm f/8	18-50mm at 50mm f/8
18-50mm at 18mm f/2.8	18-50mm at 50mm f/2.8

Below is our lens test data. To find out how to use these graphs look at this article: How we test lenses

Verdict
This lens is small for an f/2.8 model and although it suffers slightly at the wide-open aperture the focusing ability throughout the focal range warrants the aperture. From f/4 onwards it is a cracking lens that is light enough to have fitted to the camera permanently as a walk-round lens. It left me feeling that the extra price paid over the standard DC lens was well worth it. A highly recommended lens.

In summary the main positive points of the Sigma 18-50mm f/2.8 EX DC are:
Quick, accurate autofocus
Small and light for an f/2.8 lens
Sharpest lens tested to date
Useful protective pouch

Negative points are:
CA wide open
Slight distortions at either end (Minor point)

Check the latest price of the Sigma 18-50mm here

Test by Ian Andrews www.wildaboutkent.co.uk