Amazon Customer
***NOTE: Original Review was written July 2013 - UPDATE September 2014 written at bottom of page**** **************************************************************************************************** This lens is very sleek in appearance and somewhat tightly made. It operates very smooth and mounts firmly into place. The visual appearance is a subjective thing, but I find this new design by Sigma to be quite appealing. Focus is silent, quick, and overall accurate as well, though not as accurate as other zooms I have used and especially my primes. Alternative to these compliments, I have to say, unless you photograph center based subjects at less than infinity distances where borders do not matter, you will have some challenges. As noted by both photozone.de and lenstip.com, the wide end of this lens (17-24mm) is quite soft outside the center of images, 24-35 has some softness on the borders and stopping down beyond f5.6 stops does not alleviate the issue. If you use this lens for portrait or close focusing you will never see this issue. In fact, for portrait and close focus, images are quite pleasing and this lens has very smooth, uniformed bokeh with no coma (coma being where an image has a doubling effect - edges of objects will have 2 or more edges instead of one). Overall, images are somewhat clean, but there are CAs to deal with at, again, the wide end of this zoom. Here is a run down of the settings and performance of the lens. ================================================= 17-24mm: Very bad field curvature which yielded soft corners. Only center was okay from f5-f7 24-35mm: Some border softness, but good center sharpness f4-f7 35-50mm: sweet spot for this lens at f5-f8 50-70mm: sweet spot from f5-f8 at center, borders softened at f5 but sharpened by stopping down to f6-f8 Vignetting was pretty bad at f4 and still noticed unless stopped down to f6 stops at 17-24mm and again at 70mm. Colors are very natural and clear. CA was very bad for this lens in any significant contrast at 17-24, but more than tolerable at 35-70 though still not good in high contrast. Auto focus was nice and quiet, mostly decisive except in lower light. Construction definitely above average, but it is plastic and does not have any Weather Seals (not to be expected at this price for a zoom given its feature set). It also felt good on my cameras. Looks really nice too. SUMMARY: ========= Up close shooting such as portrait or close focus/macros was nice, but a bit average even for a zoom. Most mid-range priced/quality zooms are good in the center at close focusing stopped down to f5.6 stops anyway. This lens allows you a 2/3 stop advantage being that it is equally sharp at f4 to f4.5 as opposed to f5.6 for any basic, standard zoom, so this is a bit of an advantage for the Sigma 17-70 C over Kit lenses or other standard zooms. On the other hand, the Tamron 28-75 is an extremely popular lens as is the Pentax 17-70 and 18-135 for Pentax users, and this Sigma 17-70 C does not have any advantages over those lenses in center resolution at all (copy variances aside). In fact, the Pentax 17-70 from 17-50mm and the Tamron 28-75 at f4 stops is equally sharp at the center, has very low CAs, and no Vignetting on an APSC sensor along with excellent sharpness corner to corner. Alternatively, the Sigma 17-70 C lacks at the corners quite a bit and has vignetting, CA, and distortions to deal with. Optical performance is always what matters most. And in the case of this Sigma 17-70, the overall image rendition outside the center was mushy at 17-24mm, borders somewhat soft up to 35mm, and landscape images were somewhat mediocre throughout the zoom range. Even when at its sharpest settings, the images lacked a certain quality or clarity needed for any detailed photography where subjects were towards infinity focus. Alternatively, this lens would be good for closer focus distances, such as portrait, but be advised, because of the border performance at 17-24 or even up to 35mm, group shots might also be a challenge if subjects are near the border of the frame and your focused more than 12-15 feet. 4-stars build quality (5 stars reserved for metal lenses and weather resistance) 4-stars auto focus (less one star for some hesitance in lower light and not being one of the faster focusing lenses I have seen) 2-stars sharpness at infinity focusing/landscape photography/architectural photography 3-stars sharpness as a portrait lens/single subject center-focused photography 3-stars for how clean images are (vignetting, CA, fringing, bokeh, coma, overall clarity) 3-3.5 stars overall. ***UPDATE SEPTEMBER 2014 I purchased yet another lens to give Sigma a chance, especially with so many good reviews on this 17-70 Contemporary lens. This time, I got a good copy of the lens so far as sharpness is concerned. I find the lens performance (sharpness) to be nearly identical as shown on DXOMark. The borders at 17-35mm are very much improved with this copy and shooting wide open (f4)at 70mm is fantastically sharp at center. All above comments in my original review do stand correct, however, as CA is rough at times from 17-24mm, and quite notable at 24-35mm in the edges in high contrast. Also, there is very strong vignetting shooting wide open to 1 stop down at all positions. I do shoot a Pentax K5iis now as opposed to a K5 and the K5iis significantly increases border performance of all my lenses and over all sharpness across the frame while reducing fringing thanks to the removal of an AA filter. So some impact is from the remarkable K5iis, but improvements are noticed in this better copy of the Sigma 17-70 C that I received this week, regardless of what camera I use. RATING FOR MY NEW LENS - 4 STARS: my new copy of the Sigma 17-70 C is a keeper. A very solid 4 star lens indeed for this copy, though previous copies I bought were flawed. Skip the Pentax 18-135 or other 17-70 lenses, and skip any lens 500 and under in this league - get the new Sigma. As with any lens manufacturer, just hope you get a good copy of the lens as sample variation is quite random. However, after so much reading, and this new experience I have had with Sigma, it is easily seen that the new Sigma makeover of 2013 has really proven itself in the year 2014. Thank you Sigma!!!