Camera Accessories

Sigma's new 10-20mm 1:3.5 EX DC HSM replaces an earlier, slower ultra-wide zoom lens that was released late in 2004. Designed specifically for DSLR cameras with ‘APS-C format' sensors, it is offered in mounts to suit Sigma, Nikon, Canon, Sony and Pentax models. As well as having a wider maximum aperture, this lens is distinguished from the earlier model by providing a maximum aperture of f/3.5 throughout the entire zoom range.


The Sigma 10-20mm 1:3.5 EX DC HSM lens. (Source: Sigma.)

Compact and robustly constructed, this lens consists of 13 elements in 10 groups with two ELD (Extraordinary Low Dispersion) glass elements and an SLD (Special Low Dispersion) glass element to minimise the effects of chromatic aberration. Four aspherical lenses provide correction for distortion while Super Multi-Layer coatings reduce flare and ghosting. An HSM (Hyper-Sonic Motor) drives autofocusing and provides fast and almost silent operation. Full-time manual focusing is also supported.

With its 102.4-degree angle of view at the 10mm position, this lens can produce striking images with exaggerated perspective.  It is also ideal for indoor photographer, where the fast f/3.5 maximum aperture can be utilised to advantage. A minimum focusing distance of 24 cm applies throughout the entire zoom range. The maximum magnification ratio is 1:6.6.

Internal focusing enables angle-critical attachments to be used without requiring re-adjustment when the focal length is changed. It also suits the supplied petal-type lens hood and is useful with polarising filters.

Measuring 88.2 mm in length, this lens has a diameter of 87.3 mm, largely because of a 10 mm wide ring at the front, which secures the clip-on lens cap and is threaded to take an 82 mm filter. The front element of the lens is only 48 mm in diameter and bulges slightly forward, although not dramatically so.

Build quality is excellent; the lens has a ‘quality' look and feel and a very solid mounting plate. The focusing ring, which is approximately 11mm wide and has a narrow gold band around its leading edge, sits in just behind the front of the lens. It has a ridged, rubber coating and can be turned through a full 360 degrees.

Just behind it lies a distance scale with seven settings in metres and feet, ranging from the closest at 0.24 m to infinity. Behind the distance scale is the zoom ring, which is 22 mm wide and has a 15 mm wide, ridged rubber grip. In front of this grip are engraved markings showing the following focal length settings: 10mm, 12mm, 14mm, 17mm and 20mm. A slider on the non-moving section of the lens barrel behind the zoom ring switched between auto and manual focusing.

Handling
The review lens was a comfortable match to the Canon EOD 40D body we used for our tests. The metal mounting plate fitted snugly, without being either tight or too loose and it was easy to fit and remove the lens when required. The zoom movement was smooth and positive throughout the zoom range.

Moving from the 0.24 metre mark on the distance scale to the infinity position required the focusing ring to be turned through approximately 180 degrees and provided a high level of manual focusing precision. Spanning the zoom range requires less than a 90-degree rotation.

No zoom lock is provided and we found none was required as we observed no tendency for the lens to slide forward when it was carried pointing downward. 

Performance
Photo Review's Imatest tests showed the review lens delivered its best performance between f/4 and f/8 and highest resolution with the 20mm focal length. Beyond f/11, resolution tailed off as the influence of diffraction increased.

Interestingly, even the highest resolution figures we obtained failed to meet the potential of sensor in the Canon EOS 40D camera we used for testing, although the best Imatest results came reasonably close. Edge softening was detected at all focal length settings and was greatest at maximum apertures for the 12mm and 14mm focal lengths, as shown in the graph below.



Subjective assessment of test shots showed they lacked the dynamism and snap that characterise top-quality optics. However, the application of post-capture unsharp masking produced JPEG images that could be printed with adequate contrast and definition. We were able to obtain even better results when the originals were raw files.

Lateral chromatic aberration was lowest with the 20mm focal length setting but measurements fell mostly within the ‘low' range, although the 10mm focal length showed moderate chromatic aberration, as did the 14mm focal length from f/6.7 on. The graph below plots our measurements for different aperture and focal length settings.

Very slight coloured fringing could be detected at the edges of shots taken with the 10mm focal length, although none was visible in shots taken at 20mm. Edge softening was also more apparent with the 10mm images, as was rectilinear distortion.

Not unexpectedly for such a wide-angle lens, barrel distortion was obvious in shots taken at 10mm and pincushion distortion could be seen in shots taken with the 20mm focal length setting.  In the 10mm shots, flat surfaces give the impression of curving out towards the camera, as shown in the sample image below. Interestingly, if you line up a straight edge along one of the borders of the frame, no evidence of curvature is seen, although the image field will be curved because of the distortions inherent in the ultra-wide lens.

Perhaps surprisingly - and unusually for an ultra-wide lens - we could find no evidence of vignetting at any focal length setting, even at f/3.5. Flare was generally well-controlled for such a wide-angle lens.

Bokeh wasn't spectacularly attractive - but that's to be expected for an ultra-wide lens with multiple aspherical elements. This is pretty much a non-issue, since this lens is unlikely to be used for either portraits or close-up shots.

Buy this lens if:
- You need a fast, robustly built, ultra-wide zoom lens for an entry- and mid-level DSLR.
- You're happy to edit your shots and introduce post-capture sharpening.
- You shoot raw files.

Don't buy this lens if:
- Your DSLR has a 36 x 24mm sensor.
- You want close-up versatility and performance. 

IMATEST GRAPHS

SAMPLE IMAGES


10mm focal length, 1/362 second at f/13.5.

Crop from the centre of the above image at 100% enlargement.

Crop from the edge of the same image at 100% enlargement showing distortion and coloured fringing.

20mm focal length, 1/362 second at f/11.

 
Crop from the centre of the above image at 100% enlargement.


Crop from the edge of the same image at 100% enlargement showing slight coloured fringing.

10mm focal length, 1/500 second at f/13.5.

20mm focal length, 1/181 second at f/9.5.

Close-up: 10mm focal length, 1/30 second at f/11.

Close-up: 20mm focal length, 1/22 second at f/11.

Distortion: 10mm focal length, 1/15 second at f/8.

Distortion: 20mm focal length, 1/10 second at f/8.


Flare: 10mm focal length, 1/350 second at f/11.

11mm focal length, 1/181 second at f/8.

20mm focal length, 1/125 second at f/6.7.

10mm focal length, 1/362 second at f/11.

18mm focal length, 1/400 second at f/11.

20mm focal length, 1/250 second at f/11.

Picture angle: 63.8-102.4 degrees
Maximum aperture: f/3.5
Minimum aperture: f/22
Lens construction: 13 elements in 10 groups
Lens mount: Available for Sigma, Canon, Nikon, Pentax & Sony ‘APS-C format' DLSRs
Diaphragm Blades: 7
Focus drive: HSM (Hyper-Sonic Motor)
Minimum focus: 24 cm
Maximum magnification: 1:6.6
Filter size:  82 mm
Dimensions (Diameter x L): 87.3 x 88.2 mm
Weight: 520 grams