Sigma 17-50mm f/2.8 EX DC OS HSM

Name: Sigma 17-50mm f/2.8 EX DC OS HSM
Brand: Sigma
Rating: 7.9 (11 reviews)

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Specifications
Description
IS Test

17-50mm	$634 average price

Lab Test Results

Canon 7D

Blur
Chromatic Aberration
Vignetting
Geometric Distortion

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SLRgear Review
September 5, 2012
by Andrew Alexander

Announced in February 2010, the Sigma 17-50mm ƒ/2.8 EX DC OS HSM provides third-party competition in the short zoom lens market. This is the first zoom lens produced by Sigma in this range that provides both a fixed maximum aperture and optical image stabilization.

Designed for the APS-C sized camera bodies, the lens provides an effective field of view of 27 - 80mm (Canon) or 26 - 75mm (Nikon and others). The LH825-03 (583) petal-shaped lens hood ships with the lens. The lens takes 77mm filters and is available now for around $700.

Sharpness
The Sigma 17-50mm ƒ/2.8 OS offers sharp central performance throughout its zoom range, with varying degrees of corner softness. This corner softness is improved as the lens is stopped down, and there are a few points of tack-sharp image quality.

Used wide open at wide angle (17mm, ƒ/2.8) produces the ''worst'' corner softness - but even here it is comparatively light, matched nicely with a generous central area which is very sharp. As the lens is stopped down this corner softness abates gracefully, offering excellent sharpness by ƒ/5.6 (which is actually the best setting: diffraction limiting appears to set in at ƒ/8, noticeable by ƒ/11). Stopping down to ƒ/16 or ƒ/22 produces light softness across the frame.

The preceding is actually a good descriptor for performance in the other focal lengths, with a single noteworthy observation. Zoomed in to 21mm, 28mm or 50mm, corner performance is actually slightly better at these focal lengths, but there is an interesting deviation at 35mm where we see corners similar to those at 17mm. These are small numbers, so it's doubtful that you will see a meaningful impact in real-world photography, but it's interesting to note.

The sharpest point for this lens appears to be 50mm at ƒ/8, where performance is essentially tack-sharp across the frame.

Chromatic Aberration
The Sigma 17-50mm ƒ/2.8 produces CA of the magenta-green variety, noticeable in areas of high contrast, and predominantly in the extreme corners. It's mostly significant when the lens is used wide open, though zooming in does appear to limit its presence.

Shading (''Vignetting'')
Corner shading isn't a huge factor with the Sigma 17-50mm, producing (at its most notable) extreme corners which are just over a half-stop darker than the center of the frame, when the lens is used at 17mm and ƒ/2.8. Other focal lengths used at ƒ/2.8 produce around a third of a stop darker corners; other apertures do not produce any significant corner shading.

Distortion
Distortion is typical for a wide-angle zoom lens; barrel distortion when zoomed to wide, approaches no distortion in the middle, and gets a bit of pincushion distortion at the telephoto end. At its worst, distortion is around 0.75% barrel when used at 17mm. The distortion is fairly linear, and meets at the zero-distortion point at around 24mm. After that it's pincushion distortion in the corners: about -0.3%. You can turn your curves back into straight lines easily with most image processing software.

Autofocus Operation
The Sigma 17-50mm ƒ/2.8 OS is designated as an HSM (hypersonic motor) lens, but it doesn't share the full implementation of what we've come to expect from Sigma's HSM lenses. Specifically, it doesn't feature full-time manual override, so if you want to override autofocus results you must first disengage the autofocus. Due to the lens' short focus throw, focusing is quite quick, at around one second to focus from close-focus to infinity, and the lens makes very little noise in the process. Attached 77mm filters will not rotate while focusing.

Macro
The lens offers fair macro performance: 0.2x magnification, with a minimum close-focusing distance of 28cm (just under one foot).

Build Quality and Handling
The Sigma 17-50mm ƒ/2.8 OS features an all-black, all-plastic construction; parts of the lens are coated with Sigma's rubberized coating, which offers good traction. There are two switches on the lens, one to activate or deactivate image stabilization, and one to enable or disable autofocusing. The lens features a distance scale, but doesn't offer a depth-of-field scale. The lens mount is metal, and the 77mm filter threads are plastic. The aperture is made up of seven curved diaphragm blades, which should offer pleasing out-of-focus background elements.

The focus ring is mounted at the end of the lens, 3/8-inch wide and composed of raised rubber ribs. As mentioned, the focusing range of the ring is fairly small, only 45 degrees, making manual focusing a bit tedious. We found that the focus ring has very little dampening, letting it turn very freely. The focusing throw is bounded on either side by hard stops. The front element doesn't rotate while focusing.

The zoom ring is the larger of the two, 3/4-inch wide, also composed of large raised rubber ribs. There are around 45 degrees of rotation in the zoom ring, and a nice level of resistance to the ring; not too tight, and not too loose. There's no evidence of zoom creep, but Sigma does include a zoom lock to fix the lens at 17mm so the lens will not extend while dangling on your neck strap.

The Sigma 17-50mm f/2.8 OS employs Sigma's optical stabilization. In our testing of it, we noted 2, if not 2 1/2 stops of hand-holding improvement: check our IS Test above for further detail.

The included lens hood (LH825-03 583) is of the petal-shaped design, adding a further 1 1/2 inches to the overall length of the lens. The interior of the hood is deeply ribbed to reduce the impact of any stray light entering the front element, and the hood can be reversed onto the lens for storage.

Alternatives

Tamron 17-50mm ƒ/2.8 XR Di II VC LD Aspherical IF SP AF ~$650
Tamron's design has been around a while: Sigma's offering tests as slightly better, with better results for sharpness and corner shading. Operationally, they are about the same.

Sigma 18-50mm ƒ/2.8-4.5 DC OS HSM ~$400
If you don't need the constant f/2.8 aperture, Sigma offers a slightly less expensive variable aperture lens which also tests very well.

Canon EF-S 17-55mm ƒ/2.8 IS USM ~$1,150
Canon's offering in this category is about twice as expensive, and offers similar if slightly better performance than the Sigma. Operationally the autofocus system is much better and potentially the build quality as well.

Nikon 17-55mm ƒ/2.8G ED-IF AF-S DX ~$1,250
Nikon's offering in this category is about twice as expensive, and offers similar performance. Nikon's autofocus system is better than Sigma's in this case.

Pentax 16-50mm ƒ/2.8 ED AL IF SDM SMC DA* ~$750
We haven't yet tested Pentax's offering in this category.

Sony 16-50mm f/2.8 DT SSM ~$700
Sony's offering is similar to Sigma's but probably represents a better value: it's about as sharp, but uses better SSM focusing than Sigma's implementation of HSM.

Conclusion
There's no shortage of lenses to choose from in the short zoom category, and Sigma's offering presents an economical alternative to the major manufacturer's options. Optically it tested well, and it's not too hard on the pocketbook.

Product Photos

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.