Sigma 18-200mm f/3.5-6.3 11 DC OS HSM Lens for Canon

Product Information

At the smallest focal distance, you get a nice amount in the frame, although you get some distortion in the bargain. This is a serious shortcoming compared to Nikon's 18-200mm VR, on which you the focus ring never turns unless you move it, and which you may move at any time for instant manual override. I was highly skeptical that this lens could produce even reasonable optical quality throughout the focal length (FL) range. Corner sharpness does fall off a bit in the 18-28 mm range, even stopped down, but only a bit, and contrast remains reasonably good and there is relatively little visible CA. The close focusing ability is great, and for this the fact that the maximum focal length decreases as you focus closer doesn't hurt--by the minimujm distance, field of view is about the same as a 100mm macro lens, meaning so are depth of field and perspective effects, and I like 100mm macros. One of the things I am noticing with the very high density APS-C 50D sensor is that diffraction starts eroding image sharpness by f/8.

Distortion is usually invisible, but if you have a straight line running along an edge, you may see it. The photo above shows it at its worst, and unless you're shooting buildings for a living, not as bad as I make it out to be. As is typical of wide-angle lenses, CA is exacerbated in the corners of the image when used at wide-angle settings (18mm), where we see increasing amounts of CA as the lens is stopped down (3-6/100ths of a percent of frame height throughout, 7-9/100ths of a percent in the corners). CA performance is fairly constant between 135mm and 200mm, just slightly worse than the midrange, but better than wide-angle performance. The center sharpness at 18 mm is already good starting at full aperture and that increases even more after stopping down 1 stop. After stopping down 2 stops, the corner sharpness is nicely close to the center sharpness. That doesn’t apply for the longer focal distances, where the sharpness in the corners lags behind the center sharpness. In the range of 20 to 90 mm, the Sigma 18-250 mm (where the corners improve with stopping down) appears to perform somewhat better; at 200 mm, the Sigma 18-200 mm seems to do it better. In the whole, it’s an even match between the Sigma 18-250 mm and the Sigma 18-200 mm C, when it comes to sharpness.Set to 18mm, wide-angle performance is good wide open at ƒ/3.5 (sharp in the center, mdoerately soft in the corners), becoming excellent as you stop down to ƒ/5.6, where it is essentially sharp across the frame. Diffraction limiting begins to set it at ƒ/8, though it doesn't impact on sharpness until ƒ/16; even at ƒ/16, we're seeing only 2 blur units across the frame. Using the ƒ/22 aperture setting produces a softer image, at 3 units across the frame.

The Nikon offers 7 diaphragm blades compared to the Canon's 6 rounded blades; the Nikon is also slightly lighter by 35 grams. The Nikon is an AF-S lens, offering full-time manual override of focus; the Canon has a slightly closer minimum focusing distance (5cm). Both lenses have approximately the same transitions between apertures and focal lengths (ie., the minimum aperture shrinks at about the same rate as the lens is zoomed in). At 200mm, I am getting solid results at 1/20 sec. with some even longer exposures resulting in sharp images.

Ease of Use

HSM (Hyper Sonic Motor) delivers high AF speed and extremely quiet performance. With the latest AF algorithm, smoother AF is achieved. This lens competes directly in the 'stabilized superzoom' market with the Nikon 18-200mm F3.5-5.6G AF-S VR DX, Canon EF-S 18-200mm F3.5-5.6 IS, and Tamron 18-270mm F3.5-6.3 Di-II VC, all of which which we've reviewed over the past year. Its main advantage at the moment is that it is considerably cheaper than any of these other lenses, making it much the most affordable option for users looking to supplement their collection with a general-purpose travel lens. But in this case, does cheaper also mean inferior, or has Sigma delivered quality on a budget? Headline features