Announced at PMA 2010 in February, the new Sigma AF 8-16mm f/4.5-5.6 DC HSM lens is designed specifically for DSLR cameras with APS-C size image sensors and boasts the widest angle of view of its type. It covers angles of view equivalent to a 12-24mm lens in 35mm format (12.8-25.6mm on Canon cameras) and features a number of exotic glass elements that help to keep its size compact and weight relatively low.
Sigma's AF 8-16mm f/4.5-5.6 DC HSM lens shown without its end caps. (Source: Sigma.)
It's not a particularly fast lens - despite the amount of glass it contains. However, it is relatively unhampered by the rectilinear distortion that plagues most ultra-wide lenses. The new FLD elements probably make some contribution to minimising distortion because this type of glass claims to have a lower refractive index and lower dispersion than regular optical glass.
The retrofocal design of the lens is relatively complex, with 15 elements arranged in 11 groups. In addition to the four FLD elements Sigma has included other exotic glass elements to make the lens relatively compact for the wide angles of view it covers. One hybrid aspherical lens and two glass molded elements are included to correct residual distortion and astigmatism.
Super Multi-Layer Coatings have been applied to minimise flare and ghosting, while the built-in HSM (Hyper Sonic Motor) to support quiet, high speed autofocusing while also enabling full-time manual focusing in AF mode. (Some Pentax DSLRs don't support HSM focusing.) Internal focusing and zooming means the front element doesn't rotate during focusing and the overall length of the lens remains unchanged throughout its zoom range.
The front elements of this lens bow outwards, making it impossible to attach conventional screw-in filters - or even a conventional lens cap. A fixed, petal shaped hood provides some protection against knocks and reduces the entry of stray light in contre-jour situations.
Sigma provides an additional tube that slips over the lens hood and allows a lens cap (supplied) to be fitted. You can shoot with this tube in place at the 16mm focal length position but vignetting (edge darkening) will occur at all other focal lengths, becoming increasingly severe as the focal length is shortened. Similar vignetting will occur if this lens is used with DSLR cameras with image sensors larger than APS-C size or 35mm SLR cameras.
Build and Handling
As you would expect from the price of this lens, the 8-16mm f/4.5-5.6 DC HSM is very well built. The main barrel appears to be made from metal. Although the focusing and zoom rings and lens hood look and feel like plastic, it's a dense, high-quality polycarbonate and all components fit snugly to ensure a neat and elegant appearance.
The stainless steel mounting plate fitted positively and easily to the Canon EOS 40D camera body we used for our tests. From the camera body to the tip of the lens hood, this lens measures 105.7 mm. Its 75 mm diameter is modest for such a wide-angle lens.
The focusing ring lies immediately behind the lens hood. It carries a 12 mm wide ridged rubber-like band and rotates through roughly one quarter of a turn with a silky-smooth movement. Just behind the focusing ring is a distance scale, which is set into the barrel beneath a clear plastic window. It carries distance markings in metres and feet, ranging from 0.24 metres (the closest focus) to infinity.
Aft of the distance scale lies the zoom ring, a 25 mm wide band with a 13 mm wide ridged rubber-like grip. Distance markings for the 8mm, 10mm, 12mm, 14mm and 16mm focal length settings are stamped along the front of the zoom ring in bright, while lettering. Roughly one eighth of a turn is required to move from the 8mm to the 16mm position - or vice versa.
Behind the zoom ring the barrel is fixed in place for approximately 20 mm. This section carries the AF/MF slider switch, which is raised a couple of millimetres above the surface of the barrel. This section of the barrel carries patches of shallow ridges, which are presumably provided to improve its grip.
Performance
One of the most attractive features of this lens is the interesting perspective it provides on the subjects you photograph. As expected for such a wide-angle lens, distortion is inevitable - particularly at the widest angles of view - but, unlike many even modestly wide-angles lenses, this lens is comparatively free from the obvious barrel distortion that makes parallel lines bow out towards the edges of the frame.
Instead, the subject appears to be ‘mapped' on the sensor by progressively stretching it towards the periphery of the frame. And, while the result is not exactly natural-looking, it's nowhere near as disturbing as seeing lines that should be straight rendered like the staves in a barrel. Most of these ‘mapping' distortions are under control from 12mm onwards. Nevertheless, in our standard distortion tests we found some barrel distortion at 8mm and pincushion distortion at 16mm.
Imatest showed the review lens to be more than capable of matching the potential of the sensor in the EOS 40D and delivering good resolution throughout the zoom range. Diffraction began to reduce performance from about f/11 onwards but real reductions in sharpness only became evident from about f/14. The graph below shows the results of our Imatest testing.
Lateral chromatic aberration was very well controlled and remained within the ‘low' and ‘negligible' bands throughout our Imatest testing. The FLD elements appeared to have played an important role here as few wide-angle zooms perform quite as well. No coloured fringing was found in shots taken in bright and contrasty conditions. The graph below shows the result of our tests.
Vignetting at wide apertures is always an issue with ultra-wide lenses and the 8-16mm f/4.5-5.6 DC HSM is no exception, particularly with the 8mm focal length setting. You have to stop down to at least f/8 to reduce it to acceptable levels.
Flare is also difficult to avoid, particularly with the shorter focal lengths. However, this lens produced relatively little flare for its specifications and contrast was largely retained in backlit shots. A couple of shots included small flare spots due to reflected light but, otherwise performance was excellent.
Because of its wide angle-of-view, this lens isn't really suitable for close-ups and bokeh is seldom a consideration. However, the 24 cm minimum focus enables close-ups to be taken with the 16mm focal length - provided the subject was large enough.
Buy this lens if:
- You want an ultra-wide zoom lens with low rectilinear distortion for landscape or architectural photography.
- You require professional performance and build quality at an affordable price.
- You want high resolution at all focal lengths, along with acceptable flatness of field.
Don't buy this lens if:
- You'd like built-in image stabilisation.
- You need close focusing and macro capabilities.
- You need a general-purpose lens that can handle a wide range of subject types.
- You like using filters.
IMATEST GRAPHS
(based on JPEG files from the Canon EOS 40D)
SAMPLE IMAGES
Vignetting at 8mm.
Vignetting at 16mm.
Barrel distortion at 8mm.
Slight pincushion distortion at 16mm.
8mm focal length; 1/395 second at f/16.
16mm focal length; 1/322 second at f/18.
16mm focal length; 1/250 second at f/18.
8mm focal length; 1/332 second at f/14.
Extreme contre-jour lighting at 8mm; 1/500 second at f/18.
Extreme contre-jour lighting at 16mm; 1/500 second at f/22.
Close-up at 8mm; 1/41 second at f/4.6.
Close-up at 16mm; 1/30 second at f/5.6.
8mm focal length; 1/197 second at f/11.
8mm focal length; 1/197 second at f/11.
8mm focal length; 1/197 second at f/12.9.
16mm focal length; 1/99 second at f/9.9.
10mm focal length; 1/99 second at f/9.1.
8mm focal length; 1/99 second at f/8.
8mm focal length; 1/332 second at f/14.
8mm focal length; 1/332 second at f/14.
Picture angle: 114.5 degrees to 75.4 degrees
Maximum aperture: f/4.5-5.6
Minimum aperture: f/22
Lens construction: 15 elements in 11 groups (includes 4 FLD glass elements, one hybrid aspherical lens and 2 glass moulded elements)
Lens mount: Available in mounts for Sigma, Canon, Nikon, Pentax and Sony/Minolta SLR cameras
Diaphragm Blades: 7
Focus drive: Hyper-Sonic Motor (HSM)
Minimum focus: 24 cm
Maximum magnification: 1:7.8
Dimensions (Diameter x L): 75 x 105.7 mm
Weight: 555 grams