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
www.lamarlamb.com/Things/Testing-Sigma-17-50mm-f28-OS/26935388_MqHphg#!i=2257949078&k=QzNjTXT reviewed December 7th, 2012 [purchased for $609]
9 out of 10 pointsand recommended by jsonic [1 reviews]
light, well build, near silent OS, superb optics
focusring does turn and no full time manual focus
I was waiting for this lens to become available as I was looking for this type of lens for shooting weddings. I also looked at the Canon 17-40 4.0L and EF-S 17-55 2.8 IS I was very interested to see how well the new FLD glass would perform after reading very good reviews of other lenses with this type of glass. After comparising the lenses I dropped the Canon EF-S 17-55 2.8 IS from my shortlist mainly due to the high price and less than stellar build quality. The 17/40 4.0L is an impressive lens with stellar build quality but does not have IS. I do consider IS and 2.8 as a bonus as light conditions during weddings can be very troublesome so having a 2.8 lens can help focussing [also 2.8 means high precision AF] and IS helps to avoid camerashake so I can use slower flash sync speeds to get a more natural looking picture when flash is needed.
So I went home with the Sigma and boy does it perform... It is stunningly sharp even wide open and it gives me very clear, brilliant beautiful pictures with great microcontrast. It has the same brilliant high quality picture feel as for instance the 70-200 4.0 L IS
The FLD glass sure is doing a great job as abberations are almost completely absent as is purple fringing that can be a pain on these wider lenses [my Canon 20-35 has very high levels of it] I did take a picture of a military chopper against a very bright sky and there is none aberation visible... Compared to my Canon 20-35 and even my Sigma 24-70 2.8 HSM it has clearly beter optics as also the distortions are well controlled. Bokeh quality is also good, it has rounded blades which give a nice even background blur.
Mechanicaly it was suprising to see a rotating focus ring on a EX lens. I guess it is done to keep the lens as small as it is. ALso full time manual focus is not available. Both points are a pity as it would have it made mechanical and ergonomical even better. The AF is on the other hand very precise and fast, I had no problem tracking cars that where doing 70kph. The OS is the best I have seen from Sigma yet, it is completely silent [in fact I had to held my ear on the lens to hear it as I thought that it did not work] It is also effective. There is no play in the zoom and focus ring and the tube when zooming out to 50mm has no play as well. Although being light it does have a quality feel about it as to be expected of an EX lens. The swithces are precise and have a nice click to it, a definite improvement over earlier lenses.
So all in all I am very content with this little marvel and I am looking forward to do my first weddding shoot using it.