The Holy Grail of DSLR normal-zoom lenses is to have lots of zoom with lots of wide open aperture. That of course, necessitates "lots of cost." Good, light, cheap: pick two but you can't have all three. To that end, the Sigma 17-70mm in its various incarnations has always been a modest blend of all three of those qualities, being reasonably good, moderate in weight and fairly priced... having all three but not excelling in any one particular area. So then, can the "C" version improve on that formula?
The 17-70mm f/2.8-4 has already had two prior versions:
- 17–70mm f/2.8–4.5 DC MACRO HSM
- 17–70mm f/2.8-4.0 DC OS MACRO HSM
The first version was an interesting alternative to Nikon's AF-S ED 18-70mm f/3.5-4.5G IF DX, offering the same focal length range but with a faster aperture throughout. The addition of the OS designation in the 2nd generation made the lens fast and stabilized, something that casual shooters covet in a walk around lens. The new C version ("Contemporary") is actually a resigned lens and not just a refresh of the OS MACRO version. The prior version of this lens had 17 elements in 13 groups, while the new lens has 16 elements in 14 groups. It maintains three aspherical lens elements, but adds two more low-dispersion elements. The benefits include:
- Slightly greater macro capability (1:2.9 vs 1:2.7
- Lighter weight (470g vs 535g)
It could be argued that the previous lens was already good enough that a redesign was not necessary. From a purely product design standpoint, that is true, but given the popularity of this lens and the success of Sigma's Global Vision revamp, it would have been poor marketing not to have included this lens.
Body and Design
The Sigma 17-70mm OS is by moderns standards quite a small lens, and isn't much longer or fatter than your typical kit 18-55mm lens, though it does have a bit more heft. The build and design is in keeping with the the lenses in the refreshed Global Vision line-up, meaning that it's shed the drab matte appearance of the previous generation and embraced a new upscale aesthetic. The construction isn't quite up to the same standard as the Sigma 35mm f/1.4 ART, but neither is the 17-70mm as heavy (less glass inside). The texture of the plastics are quite upscale, as is the general overall appearance. The colour of the material is not quite black, but it has a deepness to it that makes it appear more than just a simple deep grey.... there's depth to how the light falls off of it that gives the plastic body a bit of an obsidian-like glassy sheen. It's certainly more attractive than the old flat black that Sigma lenses used to come in, and if you compare it to the finish of the Canon 18-55mm STM (used as an ad hoc test target below), there simple isn't any comparison. The Canon looks like a kit lens and the Sigma does not.
In fact, like the Nikon D5300, the Sigma 17-70 OS is constructed with not a conventional plastic, but a type of composite material that Sigma has branded TSC(TM), for "Thermally Stable Composite." This is a polycarbonate-based composite. The key benefit of the material appears to be that it has similar thermal expansion properties as metal, meaning that the lens as a whole can be built to smaller tolerances. This also means that the interfaces between the plastic part of the lens and the metal parts can be made smaller, reducing size and weight.
Included in the box is a petal-type lens hood, something that Canon makes you pay extra for a lens in this price range. However, it does not come with the soft case like its Sigma 17-50 f/2.8 sibling. Sigma has run into trouble with lens compatibility with newer (post 2013) Nikon cameras like the D5300. This is 100% the case of Nikon being uncooperative rather than Sigma being negligent, and as such the 17-70mm can be firmware upgraded via the optional USB dock to work with the D5300 (and other such Nikon's).
Operation-wise, there's is more good news. The lens barrel extends smoothly and has a minimum amount of wobble when fully extended. The zoom ring also rotates smoothly; however, the focus ring is a bit of an afterthought and is quite thin in comparison. This also gives you a hint of how Sigma thinks the typical buyer of this lens will use it. The lens focuses quickly, as most modern lenses do, but it's like Canon's USM (and Nikon's AF-S) lenses in terms of focus operation... great for still photography, but Canon's STM lenses focus more smoothly.
In terms of focus operation, this isn't a true Canon USM (or Nikon AF-S) type of lens, meaning that you cannot override the focus during autofocus operation. Manual focus of any kind must be done by switching the lens to full manual mode. The focus throw is fairly short as well, meaning that the lens was optimized for autofocus speed, not manual focus precision.
Covering 17 to 70mm on APS-C pretty much covers the entirety of the "normal-zoom" range. This is the EF (or FX) equivalent of 27 to 105mm, which is a bit past the typical definition of "normal" as being 24-70mm on full frame. In other words, there is a lot of versatility to this lens, if you are willing to let go of some depth of field control at the long end of the zoom range.
At 17mm, there is visible barrel distortion, though it's not excessive considering that Canon's in-camera processing engine does not correct for non-native lenses. Performance in the extreme corners is rather middling, though it does improve upon stopping down. Note: The following were taken from JPEG's out of camera from a Canon EOS 70D.
Aside from the performance at wide angles, the sharpness of this lens appears fairly consistent throughout the focal length range. Given the presence of the three aspherical and three low-dispersion elements, that would be expected, but what is unexpected is this level of consistency at this price point, which would have been unheard of just a few years ago.
This is what the bokeh looks like at short range and wide angle, using the kit lens from the 70D as a test target. Center sharpness is good at f/2.8, but enters a plateau of peak sharpness around f/4. Vignetting is in keeping with a lens of this type, and is mostly unobtrusive. Chromatic aberration control is merely average, but not objectionable. It's worse at 17mm and wide open.
This is what the bokeh looks like at 70mm and short range distance. You won't achieve results like this with subjects at typical shooting distances, but if you can get close, you can have some fun achieving background blur. Note: The following were shot with the same lens, but on the Canon SL1.
Again, peak sharpness begins one stop down at f/5.6, but there really isn't that much of a difference between f/4 and f/5.6 at 70mm. As a portrait lens, the 17-70mm can't create the soft blurred out background that a dedicated 85mm lens can, but other than that, if you position your subject in front of an appropriately non-busy background, this lens will produce nice results regardless of the deficiency in bokeh.
Conclusion and Recommendations
The new "C" version of the Sigma 17-70mm f/2.8-4 offers a lot of value for the photographer looking for something better than the kit lens options from the mainline manufacturers. This is the type of shooter who is looking for more quality but also doesn't need the depth of field control of a constant f/2.8 lens. This Sigma only gives up one stop of loss when zoomed out, but maintains consistent sharpness across the zoom range; the exception being weak corners at 17mm. If you are considering this and are stepping up from a kit lens, do yourself a favour and skip the protective U/V filter that gets slapped so often on everything with a filter thread on it. The petal hood already gives the front element some protection against accidental knocks, but more importantly, if you are are stepping up from the kit lens you ought to be looking for a tangible difference in image quality. Moving to a sharper lens and then dulling some of the image quality with a filter doesn't give you the same "wow" that a so-called "unprotected" lens does. For a lens in this price range, a filter takes away from both the value side of the equation (additional cost) and the performance side.
If you are looking at this lens, then you will probably also be considering:
- Sigma 17-50mm f/2.8 EX DC OS HSM
- Tamron SP AF 17-50mm f/2.8 XR Di-II VC LD
- Nikon 16-85mm f/3.5-5.6G ED VR AF-S DX
- Canon EF-S 15-85mm f/3.5-5.6 IS USM
- Pentax 17-70mm f/4 AL IF SDM SMC DA
- Sony 16-105mm f/3.5-5.6 DT SAL-16105
The Sigma 17-70mm is the least expensive of this group of lenses; however its 17-50mm f/2.8 sibling is quite close in price. This is comparing a newer lower-tier lens against an older upper-tier one; one suspects that the if and when the 17-50mm gets the ART makeover, the difference in price and image quality will widen. The Tamron is a similar lens in concept, but isn't priced as competitively and is does not have the same image quality. The Nikon 16-85mm and the Canon 15-85mm are the two big companies "step-up" normal-zooms, and are more expensive. Both are good lenses, but for the 'safety' of staying with the mainline brands, you pay more for lenses that are less adept in dimmer light conditions. The Pentax 17-70mm is a good all-around standard-zoom for its mount. Aside from the fact that it does not open up to f/2.8 at the wide end, it is a consistently sharp lens. However, it does suffer from higher than normal levels of chromatic aberration. Finally, the Sony 16-105mm goes back to the earlier days of the Alpha Mount; it gives loads of zoom range, but is something of a toss-up in terms of image quality. There is a 16-80mm option for Sony as well, but the as a Carl Zeiss branded optic, it is no longer in the same price bracket as the Sigma.
There is one final lens that hasn't been mentioned, and that is the older Sigma 17–70mm f/2.8-4.0 DC OS MACRO HSM. Optically, there isn't much to separate the 2nd generation lens from the "C" version. However, the "C" version is physically more attractive (if that matters to you) and is compatible with Sigma's USB dock.
With thanks to Broadway Camera.