The Sigma 18-200mm F3.5-6.3 DC Macro OS HSM ($399) is, considering its zoom range, a fairly compact all-in-one lens that’s available for Canon, Nikon, Pentax, Sigma, and Sony APS-C cameras. In full-frame terms, it covers a 27-300mm field of view. It can’t match the optical quality of a prime lens, or Sigma’s much larger and shorter 18-35mm f/1.8zoom, but images throughout the zoom range are very useable, and sharpen up nicely when the lens is stopped down.
The 18-200mmmeasures just 3.4 by 2.8 inches (HD), which is quite compact when you consider its zoom range. It does extend when zooming, doubling its height at 200mm, and it’s not that light at 15.2 ounces. The front element is static during zoom and focus, so using a polarizing filter is feasible; the lens has a 62mm filter thread. A reversible lens hood is included.
There are two control switches on the lens barrel—one toggles image stabilization (unless it’s paired with a Sony or Pentax camera; they have in-body stabilization systems), and the other switches between automatic and manual focus. The focus ring is at the front of the lens; it’s narrow, but it is easy enough to turn. The focus throw is pretty short, and you have to turn it very slowly and deliberately to get focus right—this is a lens that’s really meant to be used in autofocus mode. The zoom ring is larger; it’s covered by a ridged rubber cover and is comfortable to operate. There’s a zoom lock switch that prevents the lens from moving past 18mm; that’s useful for storage or when carrying the camera at your side, as it will keep it at its smallest.
Although its aperture is fairly narrow throughout the range, the 18-200mm focuses fairly close, so a shallow depth of field is possible under the right conditions. The minimum focus distance is 15.4 inches; at 200mm that captures images at 1:3 life size. That’s not as large as a 1:2 or 1:1 macro lens, but it does allow you to get fairly close to subjects without switching lenses.
I used Imatest to check the sharpness and distortion characteristics of the 18-200mm when paired with the 20-megapixel Canon EOS 70D. At 18mm f/3.5 the lens is at its sharpest, scoring 2,031 lines per picture height on our center-weighted test. That’s better than the 1,800 lines we use to define an image as sharp. It maintains good marks through most of the frame, although the outer edges dip to 1,416 lines. Edge and corner softness is just something you’re going to have to live with when using an all-in-one lens like this; the edges never get that sharp, even when the 18-200mm is stopped down. They do improve at f/5.6 (the center-weighted score jumps to 2,295 lines and the edges hit 1,575 lines) and at f/8 (the center-weighted score is 2,225 lines and the edges score 1,668 lines).
At 35mm the maximum has narrowed to f/4.5. The lens scores 1,722 lines per picture height here, and improves to just 1,782 lines at f/5.6. Stopping down to f/8 brings that mark up to a sharp 1,948 lines. At f/4.5 and f/5.6 the middle third of the frame between the outer edges and center is a bit on the soft side, hovering around 1,550 and 1,780 lines, respectively, and edges are murky (700 and 900 lines, respectively). At f/8 the performance across the frame is a bit more even; the mid-parts score 1,925 lines and edges top 1,200 lines.
At 75mm the maximum aperture is f/5.6, but performance is actually pretty good. It scores 1,846 lines, with midparts of the frame that hover around 1,750 lines and outer edges that approach 1,400 lines. Stopping down to f/8 improves the center-weighted score to 2,001 lines, which it maintains through most of the frame; the outer edges are a bit soft at 1,522 lines.
The aperture narrows to the minimum f/6.3 that the lens is capable of by the time you get to 145mm. Here it scores 1,739 lines, with softness at the midparts (1,619 lines) and edges (1,097 lines) of the frame. Stopping down to f/8 bumps the average score to 1,822 lines; midparts hit 1,750 lines and the edges show 1,200 lines. At 200mm f/6.3 the sharpness is 1,713 lines, a score which improves to 1,904 lines at f/8; the midparts and edges of the frame are very similar to what you see at 145mm.
So, the lens dances around our acceptable center-weighted sharpness throughout most of its zoom range, bettering it at the wider angles and falling just short when zoomed in. As you see in most lenses, narrowing the aperture improves things a bit. Distortion is another issue; at 18mm there’s some noticeable barrel distortion, about 2.5 percent; this causes straight lines to appear to curve outward. It’s enough that you’ll likely notice it in some shots, but it can be easily corrected with a software tool like Lightroom. As you zoom in the barrel distortion goes away, but pincushion distortion—which causes lines to curve inward—takes over. The lens shows 2.7 percent at 35mm, 2.3 percent at 75mm, and 1.8 percent at 145mm and 200mm. Pincushion distortion tends to be more visually noticeable in shots than barrel distortion, but it’s just as easily correctible. It’s an extra step you’ll have to perform when processing images, but one that comes along with the compromises you accept when opting for a lens with this long of a zoom range.
Despite its optical issues, we’re giving the Sigma 18-200mm F3.5-6.3 DC Macro OS HSM a four-star rating. Any long zoom SLR lens is going to come with some compromises in pure optical quality in order to achieve a manageable size and price tag. The Sigma lens is not without them, but it’s reasonably sharp throughout most of its range, and improves when stopped down. Distortion can be a nuisance, but it’s one that can be corrected via software, and it’s tough to argue with the compact design, close focus capability, and very reasonable $400 price tag. You won’t have to deal with as many compromises if you opt for a lens with a shorter zoom range—we’ve reviewed 18-135mm lenses from Canon, Pentax, and Sony, as well as the Nikon 18-105mm. None of the 18-135mm designs are as compact, or inexpensive, as the Sigma 18-200mm, but are solid options if you prefer to trade some zoom range, size, and money for a lens with fewer compromises.
|Lens Mount||Canon EOS, Nikon F, Pentax K, Sony A, Sigma SA|
|35-mm Equivalent (Telephoto)||300 mm|
|Dimensions||3.4 x 2.8 inches|
|35-mm Equivalent (Wide)||27 mm|
|Optical Zoom||11.1 x|
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