Camera Accessories

Designed exclusively for digital SLR cameras with APS-C sized sensors, Sigma's new DC 18-125mm 1:3.8-5.6 HSM lens offers a slightly longer zoom range than most kit lenses and promises better optical quality. Constructed from 16 elements in 12 groups, it comes with Sigma's Optical Stabiliser function and multi-layer coatings to minimise flare and ghosting.

The optical construction of this lens includes Special Low Dispersion (SLD) glass, a moulded glass aspherical element and two hybrid aspherical lenses elements to provide high image quality throughout the entire zoom range. The surfaces of all elements carry super multi-layer coatings.

Build quality is very good, with a metal mounting plate that comes in versions to suit Sigma, Canon, Nikon, Pentax and Sony 'APS-C' DSLR cameras. Owners of Pentax and Sony DSLR cameras should note that the built-in optical stabiliser will not operate when the DC 18-125mm lens is used with cameras that have body-integrated stabilisation. Sigma's stabilisation system uses two sensors inside the lens to detect vertical and horizontal movement of the camera, moving a dedicated lens group to compensate for camera shake. The company claims it enables photographers to use shutter speeds approximately four stops slower.

Rubberised focusing and zoom rings provide a secure and positive grip, while a lock on the lens barrel prevents the lens from extending when carried on a downward-facing camera. There's no slackness in the zoom mechanism so we never really needed this facility in our tests - even though we did carry the lens pointing down from time to time.

The focusing ring is towards the front, while the broader zoom ring is closer to the camera body. There's no distance scale but the zoom ring is engraved with settings for 18, 24, 35, 50, 70, 100 and 125 mm focal lengths, while the focusing ring has paired feet and metre markings covering 1.15, 2, 3, 4, 6 and 10 feet plus 0.35, 0.6, 1, 2 and 4 metres, along with a shared infinity setting.

Sigma's HSM (Hyper Sonic Motor) is built into the lens mechanism to ensure quiet and high-speed autofocusing. In our tests it fulfilled both promises. Sliding switches on the barrel allow autofocusing and optical stabilisation to be turned on and off. This lens has a minimum focusing distance of 35cm at all focal lengths, along with a maximum magnification ratio of 1:3.8, making it ideal for close-up photography.

We're not sure what accessories come with this lens as it was supplied with only the front and rear caps. No documentation was provided and there's nothing on Sigma's website (or local distributor, C.R. Kennedy's) to indicate whether a lens hood or carrying pouch were provided. The front of the lens carries a screw thread that accepts 67mm filters.

Handling
The review lens was a rather tight fit when we mounted it on the EOS 40D body we used for most of our tests. It's slightly heavier than the kit lenses most manufacturers supply with entry- and mid-level cameras. However, when mounted, it proved a comfortable match for both the EPS 40D and the much lighter EOS 1000D (which we used for some test shots).

The HSM drive was quiet and autofocusing was fast and accurate, only slowing slightly at low light levels and with subjects where contrast was very low. Both the focusing and zoom rings moved smoothly and positively. Moving from the 18mm to the 125mm focal length requires a quarter of a turn and extends the lens barrel by just under 5 cm. Setting intermediate focal lengths was relatively easy, although the accuracy of the engraved focal lengths was not particularly high for the settings at the middle of the focal length range.

The focusing ring moves through about an eighth of a turn and feels a little slacker than the zoom ring. The degree of precision provided is not as high as we would like but adequate for most purposes. 

Performance
Imatest showed the Sigma DC 18-125mm 1:3.8-5.6 HSM lens to be a competent - although not stellar - performer. Highest resolutions were obtained at wide apertures and wider angles of view, with a gradual decline in resolution as the lens was stopped down and focal length increased. A moderate level of edge softening was detected. The graph below shows the results of our tests across all focal length and aperture settings.

Lateral chromatic aberration was also very well controlled and remained in the 'insignificant' or 'low' zones for all lens aperture/focal length combinations. The graph below shows the results of our Imatest tests, using figures for the edge of the frame (where C.A. is more likely to be visible). The red line at 0.04% delineates the border between the 'insignificant' and 'low' zones.

We found no evidence of vignetting (edge darkening). Barrel distortion was observed in test shots taken with the 18mm setting but it vanished by 25mm to be replaced by slight pincushioning at 35mm. This pincushion distortion increased very gradually to the 125mm focal length setting. At no time was either distortion severe enough to affect everyday photography.

Flare was only visible when the camera was pointed directly towards the sun and even then it was reasonably well controlled. Bokeh was soft and quite attractive.

The image stabilisation system was challenged at shutter speeds slower than 1/20 second when focal lengths longer than 50mm were used. However, it proved advantageous when shooting with the 125mm focal length setting.

SAMPLE IMAGES 

 
125mm focal length, 1/40 second at f/5.6.

 
110mm focal length, 1/500 second at f/5.6.

 
18mm focal length, 1/60 second at f/11

 
125mm focal length, 1/250 second at f/8.

 
55mm focal length, 1/800 second at f/5.6

 
125mm focal length, 1/15 second at f/6.3.

Focal length range: 18-125mm 
Picture angle: 69.3 - 11.4 degrees
Maximum aperture: f/3.8
Minimum aperture: f/22
Lens construction: 16 Elements in 12 Groups
Lens mount: Sigma, Canon, Nikon, Pentax, Sony
Diaphragm Blades: 7
Minimum focus: 35 cm
Filter size:  67mm
Dimensions (Diameter x L): 74 x 88.5 mm
Weight: 505 grams