Introduction

Sigma 12-24mm f/4.5-5.6 EX DG HSM is one of about half a dozen ultra wide zoom lenses in Sigma's modern lens lineup. This is also one of the widest full-frame zoom lenses available on the market at this time (there are a couple of 'wider' APS-C type lenses offered by Canon, Tokina as well as Sigma itself). The lens sells for ~US$600 (as of September 2007) and it this price remains more or less affordable for mainstream consumers looking for a wide zoom. Since the lens is designed for a full-frame mounts, on APS-C type cameras with 1.6x crop factor (like Digital Rebel XTi) it will have a field of view similar to that of a 19-38mm zoom lens on a full-frame body.

The optical construction of the lens consists of 16 elements in 12 groups, including 3 aspherical glass elements that correct linear distortion and 4 SLD glass elements to correct color aberration. The build construction of the lens is pretty good - the lens parts do not wobble, rubberized focus and zoom rings are very smooth and the overall look and feel is very sturdy. The lens has a bulging front glass element that extends out a few milliliters so users should be careful not to bump it into something during a photo session. The good news is that a built-in petal shaped lens hood will provide some protection here. Sigma also includes an open-faced lens cap holder that aside from holding the actual lens cap allows attaching screw-in type 82mm filters.

The lens features a silent and fast Hyper Sonic Motor for AF focusing as well as full-time manual focusing system that can be controlled by an AF/MF switch on the side of the barrel. Like most modern lenses, Sigma 12-24mm f/4.5-5.6 EX DG HSM does not have a dedicated aperture ring and all aperture settings are camera controlled. The minimum focusing distance is 28cm (0.92ft) and the minimum aperture is f/22. The lens is pretty bulky for an ultra-wide zoom lens - the feel is accentuated by a rather 'fat' barrel - it measured 87 x 102mm  (3.4 x 3.9in), however, at 600g (21.6oz) the lens is not that heavy.

Image

The factory box includes Sigma 12-24mm f/4.5-5.6 EX DG HSM lens, front and rear caps, front lens cap/filter holder, soft vinyl case, manual and registration card. The lens used in this test was a Canon EF mount variant, but Sigma offers this lens also in Sigma, Nikon, Sony/Minolta and Pentax mounts.

 

Summary
Lens Composition 16 elements in 12 groups
Angular Field 122 - 84 degrees
Minimum Focus 28cm/0.92ft
Focusing Action AF/MF, HSM
f-stop Scale f/2.8-f/22, camera-controlled
Filter Size Rear-type gelatin
Lens Hood Built-in
Weight 600g/21.6oz
Dimensions 87x102mm/3.4x3.9"
Lens Case Soft vinyl case

 

Field Tests

The lens showed pretty decent performance at 24mm, with both center as well as borders remaining sharp throughout the aperture range. Unfortunately, results at 12mm were somewhat of a mix bag and the lens showed noticeably softer results around borders at wide apertures. AF was pretty fast and accurate, but hunted occasionally in the dark. Color representation was more or less accurate but the lens lacked contrast, especially at the wider end of the zoom range.

 

Vignetting @ f/4.5 - full frame vs 1.6x crop (12mm)
Vignetting @ f/4.5 - full frame vs 1.6x crop (12mm)

 

Vignetting @ f/5.6 - full frame vs 1.6x crop (24mm)
Vignetting @ f/5.6 - full frame vs 1.6x crop (24mm)

 

The lens shows noticeable vignetting on a full-frame body at the wider end of the zoom range from f/4.5 through f/5.6, which is reduced with stopped down aperture and by f/11 becomes pretty insignificant. Vignetting is also reduced towards longer end of the zoom and at 24mm it's pretty minimal with wide open aperture (f/5.6) and practically nonexistent at f/8 and beyond. As expected, the lens produced significantly less vignetting on an APS-C camera, where vignetting is pretty mild at 12mm with wide open aperture and basically non-existent throughout the aperture range at 24mm. The lens also produced minor levels of color fringing across the frame pretty much throughout the zoom range - frankly speaking this does not come as a big surprise for such a wide zoom lens. Flare seemed more or less under control, partly due to the built-in lens hood. Surprisingly, distortion, which is pretty common in most ultra wide lenses, was very well maintained, and even at 12mm image borders are distorted only slightly.

 

ISO 100, 1/500, f/4.5, 12mm (100% crop)
ISO 100, 1/500, f/4.5, 12mm (100% crop)
Sigma 12-24mm f/4.5-5.6 EX DG ASPH HSM image gallery...

 

Lab Tests

Please note that MTF50 results for APS-C and Full-Frame cameras are not cross-comparable despite the same normalized [0:1] range used to report results for both types of cameras.

 

Canon APS-C: The lens showed pretty decent performance on an APS-C camera, with best overall results clustered at the longer end of the zoom range. Here the lens shows outstanding center and border performance throughout the tested aperture range. Wider end of the zoom range shows pretty good center performance throughout the aperture range and somewhat weaker border performance at the wider apertures (f/4.5-f/5.6). Performance in the center of the zoom range however was the weakest point - at 17mm and wide open aperture (f/5.6), both center as well as border performance is pretty average and only improve to decent levels by f/8. At its peak from f/8 through f/11 the lens will manage to produce outstanding 16in and decent 24in prints - not bad results for an ultra wide zoom. Conclusion? The lens benefits from its relatively small maximum aperture and managed to squeeze out a more or less decent performance at the both ends of the zoom range.

 

MTF50 (Line Width/Inch on the Print) @ 12mm
MTF50 (Line Width/Inch on the Print) @ 12mm

 

Normalized raw MTF50 @ 12mm
Normalized raw MTF50 @ 12mm

 

MTF50 (Line Width/Inch on the Print) @ 17mm
MTF50 (Line Width/Inch on the Print) @ 17mm

 

Normalized raw MTF50 @ 17mm
Normalized raw MTF50 @ 17mm

 

MTF50 (Line Width/Inch on the Print) @ 24mm
MTF50 (Line Width/Inch on the Print) @ 24mm

 

Normalized raw MTF50 @ 24mm
Normalized raw MTF50 @ 24mm

 

The lens showed somewhat high level of chromatic aberration on an APS-C camera, especially at wide aperture levels. At 12mm CA averaged ~1.4px in the center, but is reduced to ~0.8px with stopped down to f/11 aperture. CA around borders is even higher, averaging ~1.6px across the aperture range. Amount of CA is reduced slightly towards 24mm, with CA averaging ~0.7px across the aperture range in the center and ~1px across the aperture around borders.

 

Image borders @ 12mm (100% crop): f/4.5 vs f/8
Image borders @ 12mm (100% crop): f/4.5 vs f/8

 

Image borders @ 17mm (100% crop): f/5.6 vs f/8
Image borders @ 17mm (100% crop): f/5.6 vs f/8

 

Image borders @ 24mm (100% crop): f/5.6 vs f/8
Image borders @ 24mm (100% crop): f/5.6 vs f/8

 

Canon FF: The lens showed pretty much identical performance on a full frame Canon 5D, with excellent overall results at 24mm (both center and borders are outstanding throughout the aperture range). 12mm through 17mm range is somewhat weaker with wide open apertures (not disastrously weaker - just when compared to 24mm performance), and once stopped down to f/8 the lens performas quite well even in this wider range. Conclusion? Overall results are quite decent - not the best performer on the market, but not too shabby either.

 

Normalized raw MTF50 @ 12mm
Normalized raw MTF50 @ 12mm

 

Normalized raw MTF50 @ 17mm
Normalized raw MTF50 @ 17mm

 

Normalized raw MTF50 @ 24mm
Normalized raw MTF50 @ 24mm

 

The lens fared a little better on Canon 5D, with CA averaging ~0.7px in the center throughout the zoom range and the tested apertures. CA was highest at 12mm, where it averaged ~1.4px throughout the apertures, but was reduced to ~0.8px (across the apertures) towards the longer end of the zoom.

 

Image borders @ 12mm (100% crop): f/4.5 vs f/8
Image borders @ 12mm (100% crop): f/4.5 vs f/8

 

Image borders @ 17mm (100% crop): f/5.6 vs f/8
Image borders @ 17mm (100% crop): f/5.6 vs f/8

 

Image borders @ 24mm (100% crop): f/5.6 vs f/8
Image borders @ 24mm (100% crop): f/5.6 vs f/8

 

Alternatives

As mentioned earlier, Sigma 12-24mm f/4.5-5.6 EX DG HSM is one of the widest full-frame zooms available on the market. If you shoot with an APS-C camera, then you're in luck - there are three lenses you might want to consider here. The first one is another Sigma lens - 10-20mm f/4-5.6 EX DC (review) which offers outstanding (for a wide zoom lens) image quality and superb build quality at a very reasonable price. Canon's EF-S 10-22mm f/3.5-4.5 USM (review) and Tokina ATX PRO DX 12-24mm f/4 (review) are two other APS-C type lenses that are worth examining. If you're looking for the best image quality and are willing to consider more expensive alternatives, then Canon's EF 16-35mm f/2.8L II USM (review) is an outstanding and well rounded lens with superior image quality throughout the zoom range. Finally, you might also want to take a look at Canon EF 17-40mm f/4L USM (review), which shows pretty decent characteristics and is priced at a more affordable level.

 

Recommendation

Sigma 12-24mm f/4.5-5.6 EX DG HSM shows pretty decent performance throughout the zoom range from f/8 and on. At wider apertures the lens exhibits some weakness around borders (primarily in the 12-17mm range), so you should be prepared to stop down to achieve the best results. Somewhat higher chromatic aberration is another issue to consider here. However, with unusually low for an UWA zoom lens linear distortion, the overall package remains quite attractive for those of us looking for a landscape type lens.