9 out of 10 points and recommendedBuild quality, focus speed, zoom range and smoothnessEdge sharpness wide open, CA
I compared performance and test images taken with the Sigma 10-20 f/3.5 against my Nikon 16-85 VRII, which I consider my sharpest lens. The photos were taken with a Nikon D5000, tripod mounted, no digital sharpening, of fixed targets on my living room wall at about six feet. The targets consisted of newspaper at the corners and a large US map in the center, with a variety of detail and some color. Illumination was provided by house lamps and a photo flood light. The images were compared side by side at 200% enlargement on my monitor.reviewed October 2nd, 2009 (purchased for $650)
The Sigma 10-20 was not as sharp as the Nikon 16-85 in the very center of the image at comparable focal lengths (16mm and 20mm) and apertures, although was very close by f/5 and nearly the same at f/8. At the edges of the image however, the Sigma 10-20 was as sharp or sharper and had better contrast at f-stops tested, 3.5-8. I have no lenses to compare the Sigma 10-20 to at shorter focal lengths.
Focus speed with the Sigma 10-20 is very fast and quiet, similar to the Nikon 16-85. There is some variation in auto focus reproducibility but seems to be within a reasonable margin and will likely not be noticeable in most photographs. The zoom action of the Sigma lens is smoother than my Nikon lens. Zoom action is important if one likes to zoom in or out while recording video clips. The lens is somewhat larger and heavier than the Nikon, but roughly the same size.
Chromatic aberration/color fringing has been reported as being an issue with many wide angle lenses, including this lens. I will comment on this after shooting some high contrast scenes outdoors if I feel it is significant.
This is my second copy of the lens. The first copy appeared to have a slight back focus problem at 10mm at short focal distances as indicated by variations in auto focus performance vs manual focus to achieve optimal sharpness. Optically, the first copy appeared as sharp as this one and likely would have been acceptable to most users.
Edit 9-30-09: The lens performed well in the field yielding good color and contrast. Flaring is visible as the lens is tilted towards the sun. I used my baseball cap to shade the lens and would also recommend the lens hood in most situations. At 10mm, sharpness is acceptable at f3.5 in the center and quite soft at the edges. Sharpness at the edges seems fairly good by f4.5. Color fringing is quite evident in high contrast areas near the edges of the image however it was not so bright as to appear in my uncorrected 8x10 prints. Also it was quite easy to reduce the fringing to a non-issue with CA correction using Adobe CS4. Auto focus was accurate.
Overall I'm quite pleased with this lens and I'd say it outperforms my expectations for sharpness and vignetting but would have been nice to see the CA better controlled . I will keep this lens, however the older version (f4-5.6) is reported to be as good or perhaps better in some respects so I'd recommend the f3.5 lens only if the constant aperture is of interest to you.
10 out of 10 points and recommendedbuild, size, handling
Excellent lens. I'm very impressed with the build quality and handling of the lens. I've used it for just a few days so don't have any comparison images yet but wide open it is definitely quite sharp and the contrast is very good. The lens will not auto focus on Nikon bodies such as my D5000 and can take some trials to get a sharp image hand held. Using the magnified live view and a tripod I can get the focus spot on. A pleasure to use!reviewed December 29th, 2010 (purchased for $400)
10 out of 10 points and recommendedExcellent all around performer, sharp, good contrast, very pleasing buildweight, not weather sealed
Solid build and a great looking lens. The SLR Gear review is right on. Though this Sigma is large and on the heavy side, for what its giving, I'll gladly haul it around. I first tried the Tamron 24-70, another great performer optically, more expensive, but also rather heavy and more limited zoom range. I like the silent optical stabilizer on the Sigma, and the very quiet, quick focusing. The zoom and focus ring are rather stiff, I like the precision of both though some may not be comfortable with the resistance.reviewed February 15th, 2014 (purchased for $899)
I compared the resolution and contrast of this lens against various zooms and primes at similar focal lengths at f/4, f/5.6 and f/8: Nikon 70-200 f4 at 105 mm, a Nikon 85mm 1.8d, Nikon 50mm 1.8g and Tamron 17-50 dx and Tamron 24-70 f2.8 FX. As far as I can tell, the Sigma 24-105 offers very nearly the same or better resolution as any of these lenses. CA is slightly evident at the long zoom end. I rated IQ at 9 due to somewhat soft corners wide open and slight center softness at the long end, both are improved by stopping the lens down. Only compared to the best the other lenses could offer, did I notice any slight deficiency in IQ. This lens is a top performer, hopefully it proves to be reliable as well.