tcchou71's Full Review: Sigma 18-125mm f/3.5-5.6 DC for Canon EOS
This review describes my experience with this lens on a Canon 300D digital rebel.
This is a lens for which I had high hopes. It has a roughly 7x zoom range, and its wide 18mm end is particularly useful because of the 300D's 1.6x multiplier (gives 28mm equivalent). Fully zoomed, it reaches 125mm (200 mm equivalent). There is a zoom lock button to prevent zoom creep.
However, my copy of the lens front-focuses when shooting distant objects (farther than about 30 feet). Every other lens I've tried on my camera focuses perfectly (a Tamron, another Sigma, and three Canon lenses) so I'm reasonably sure the problem is with the lens, not the camera.
When this lens is in focus, pictures are impressively sharp at all focal lengths, except for some soft corners at the wide end at wide open aperture. But that is typical for consumer-grade wide lenses. In fact, the wide-angle performance is similar to the 18-55mm kit lens, which is also soft in the corners and seems to have more chromatic aberration. All in all, a respectable performance given that the zoom range is more than double that of the kit lens. Autofocus is moderately fast, although in my case not accurate.
In the end, I had to return this lens because 80% of shots I took at full zoom of distant objects were front-focused, i.e. sharpest objects were in front of what I focused on. The problem was somehow less severe with closer objects. When shooting very distant objects I HAD to use manual focus to get anything remotely acceptable. When I went to the Canon SLR lens forum at dpreview.com, I noticed quite a number of threads about front-focusing issues with the Sigma 18-125. Not every user was reporting problems, but quite a few were reporting that they needed to use various tricks (e.g. parfocal technique) to get the lens to focus right.
This lens does show more vignetting (light reduction in corners) than the kit lens. Interestingly, it's even worse than Sigma's 18-200 lens, whose truly massive zoom range would be expected to be accompanied by even worse optical sacrifice (but it isn't).
Vignetting only bothers me close to wide open aperture, and because it's correctable in software (e.g. Panotools, which is free) I'm not bothered by it as much as I am by the focus issue.
Overall, I would recommend this lens only if you buy from a dealer that lets you return it if you encounter focus problems. And now that Sigma has released their 18-200 lens, which has less vignetting than the 18-125, and seems to focus better (although it's still not perfect) I would recommend trying that lens first.
Other lenses
After being disappointed by the Sigma 18-125, I went searching for a different all-purpose lens. I have settled on Sigma's new 18-200. It focuses very well at focal lengths up to 135mm or so, and then develops a slight front-focus at longer focal lengths. One large lens review site (photozone.de) also concluded that the Sigma 18-200 misfocuses near 200mm (see link here: http://www.photozone.de/8Reviews/lenses/sigma_18200_3563/index.htm).
You can see all my lens reviews below:
Canon 100-400 - fast autofocus, good optics make very good wildlife lens. But loses some sharpness at 400mm, and performance with 1.4x teleconverter is disappointing.
http://www.epinions.com/content_171720740484
Sigma 18-200 - good optics, versatile range, but my copies misfocus near 200mm (though I can coax it into working with parfocal technique).
http://www.epinions.com/content_185158569604
Sigma 18-125. My first attempt to use a Sigma DC lens. Had front-focus problem at all focal lengths. Did not try a second copy as I switched to 18-200.
http://www.epinions.com/content_152606051972
Sigma 28-300. My first lens for my Canon 300D, purchased before Sigma released any DC lenses. It was pretty good considering its wide range, and focused quite accurately. But 28mm isn't very wide on a DSLR.
http://www.epinions.com/content_153463459460
Digital Camera reviews
I have also used a handful of small digicams, in my quest to find the perfect travel pocket camera. Here are my reviews:
Ricoh Caplio R3 - my favorite small camera, with its 7x optical zoom, 28mm wide angle, astonishingly small size, very good image color and detail, image stabilization, and voice recorder mode. But the blades that protect the shutter are weak, and easily knocked out of position.
http://www.epinions.com/content_217558847108
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