Convenient but Heavy
Written: Jun 12 '09
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Product Rating:
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Pros: Wide zoom range, fast focus, image stabilization, adequate image quality, price
Cons: Size and weight, occasional misfocus
The Bottom Line: If you want a super-zoom on a budget this will do the job and is a good choice.
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| alleng's Full Review: Sigma 18-250mm F3.5-6.3 DC OS HSM Zoom Lens for Di... |
I decided to purchase this lens after taking a couple of vacation trips with my Nikon D40 and carrying the 18-55mm kit lens plus the 55-200mm VR telephoto zoom. Both lenses worked very well, but switching between them became a pain. It seemed like I never had the correct lens on the camera when I wanted to use it. Having experienced the benefits of the Nikon 55-200mm VR’s vibration reduction feature I decided that I did not want a lens without image stabilization. I also wanted one that could focus rapidly because I was frequently using the telephoto capability to take pictures from moving vehicles and of moving objects.
There are basically 3 lenses I found that could have satisfied my requirement for an 18-200mm or greater zoom: Nikon 18-200mm VR, Tamron 18-270mm, and this one. The first choice, given my experience with their quality was the Nikon. However that lens is relatively expensive, nearly $300 more than the Sigma, and I just couldn’t see spending that much to duplicate a capability I already had, albeit with the inconvenience of having to switch lenses frequently. Reviews of the Tamron were generally good but there were several complaints that it was slow to focus. The Sigma was new, relatively low cost, and had few reviews, but reviews of previous similar Sigma products indicated that they had a fast focusing motor and were generally of good quality. Consequently I ordered this lens from a dealer with a liberal return policy in case it turned out to be unsuitable for some reason.
First Impressions
This is a solid, rather heavy piece of equipment. It weighs about 22 ounces, which is more than the whole camera with the kit lens installed weighs. It has a wide zoom ring grip that is pretty tight but with smooth motion. I had been afraid of lens creep, a situation in which the lens extends from wide angle to telephoto by itself if it is pointed downwards while on the camera. This lens has a lock button that will lock it in the 18mm position but I found that it is so tight that it has no tendency to creep even with the lock disabled. It may loosen up over time but if it does the lock button should do the trick.
There are two switches on the side of the lens to enable and disable autofocus and OS (Sigma’s optical stabilizer feature). If autofocus is disabled manual focusing is by a fairly wide ring just forward of the zoom ring. If autofocus is enabled this ring rotates by itself as the lens focus motor operates. The manual focus ring cannot be rotated by hand if autofocus is enabled. Manual focusing works but is not easy because the entire focus range is covered by only 1/8 of a turn of the ring, making its use very sensitive. Manual focus is useable, however, and it is actually easier than on the two Nikon lenses that I have because the ring is wider, smoother, and easier to grip.
The front element of the lens incorporates a large piece of glass and has 72mm filter threads. It’s easy to inadvertently smudge, so one of the first things I did was to purchase a 72mm UV filter to help protect the lens front element. The overall lens body is about 3 inches in diameter and fits the camera just fine, but it is large enough that at its widest angle setting the shadow it casts from the built-in flash becomes visible. In fact, my biggest complaint about the lens is that it is bulky and heavy. An SLR is already a lot to carry around and this lens more than doubles the weight. However the extra flexibility of not having to swap lenses is a strong incentive to go ahead and develop the necessary neck muscles to support it. In carrying it around for a couple of days for an actual photo shoot I found that I got used to it more quickly than I thought I would. It was a bit of a chore but not as bad as I had feared.
Performance
I do not have equipment to do lab tests on things like resolution and chromatic aberration but I did do some comparison shots with my two Nikon lenses. This comparison is not really fair because the two Nikon lenses each have zoom ratios of only about 3:1 while the Sigma has a zoom ratio of 13.8:1. The Nikons would be expected to do much better. The optics in this lens are very complex, comprising 18 elements in 14 groups. With this much glass moving around, it’s necessary to compromise between resolution, distortion, and chromatic aberration (color fringing). I’m happy to report that for my level of general photography, images produced by this lens were generally indistinguishable from those produced at the same focal length by the Nikon lenses. I posted a number of test shots and comparisons with the Nikon lenses at:
http://www.flickr.com/photos/7820273@N07/sets/72157618979603550/
Images were generally sharp with good color and contrast. I did observe noticeable chromatic aberration at 250mm in a very high contrast subject at the extreme edge of the image field. However this is to be expected with this kind of lens. In most situations the chromatic aberration is not visible.
The HSM (Hypersonic Motor) focusing mechanism is fast and very quiet. Focus accuracy is quite good, but not 100%. Occasionally it will focus somewhere behind or in front of the subject, especially if the subject is of low contrast and there is some kind of high contrast element nearby. This is also true of the Nikon lenses, although it seems to happen somewhat more often with the Sigma.
One anomaly resulting from the optical design is that the full 250mm focal length is only achievable at a focus distance of infinity. In one of my tests against the Nikon 55-200, I had to set the Nikon at 175mm to produce the same image size as the Sigma did at 250mm for a subject that was about 25 feet in distance. This is not generally a problem because the full telephoto capability is usually only needed at long distances, but needs to be taken into account if trying to get close-ups of nearby subjects. For subjects more than 100 feet away the true focal length is greater than 200mm.
The lens will focus down to a distance of about 18 inches at all focal lengths but the reduction in effective focal length as the subject gets closer limits the magnification obtainable. I found the lens generally good enough to get decent images of flowers but it worked better using a longer focal length from further away. The bokeh, or desired blurring of the background, when shooting things like flowers is quite smooth. For real macro photography, however, the Nikon 18-55mm kit lens produces superior results.
The lens has a maximum aperture range of f/3.5 to f/6.3 depending on the focal length. It gets to f/6.3 from about 140mm out. This is about ½ stop slower than the Nikon lens. My camera works well enough at the higher ASA settings (800 and 1600) that the slower lens is generally not a problem. But for someone who wants of photograph fast moving objects it could be an issue under low light conditions. I was afraid that focusing accuracy would be a problem at f/6.3 but it seems to work quite well. I did encounter a few situations in which the lens either would not focus or would focus incorrectly, but the same thing also happened with the Nikon 55-200 lens under some conditions. Overall, autofocus works adequately.
The image stabilization feature (OS) works quite well. Since the stabilization mechanics and electronics are built into the lens, their effect is visible through the viewfinder. I can look through the viewfinder and see the little movements while hand holding the camera, and when I depress the shutter button half way, turning on the OS, the image immediately stabilizes with no jerkiness. I was able to get sharp, handheld pictures most of the time at 1/5 second at a focal length of 18mm, and 1/25 second at a focal length of 250mm. This feature came in very handy when I photographed a religious service during which I could not use a flash. I got some very nice images that would have been impossible without OS. The Sigma OS seems to work about as well as Nikon’s VR (Vibration Reduction) feature and it’s nice to have it at wide angle as well as telephoto settings. OS is like an electronic tripod that effectively decreases the amount of light needed for shooting stationary subjects by 3 to 4 stops. Note that, like with a tripod, even if you can overcome the handheld camera motion, the motion of the subject is not affected and will cause blur. Moving objects still require fast shutter speeds.
Conclusion
I like the lens and am planning to keep it. I will not, however, get rid of my two Nikon lenses because I want to be ready for situations in which the smaller size, lighter weight, and slightly better performance of the Nikon lenses will be important.
Overall, I like the results I have been getting. The convenience of not having to swap lenses is very valuable and, in many situations, overrides the negatives of the heavier weight and the small compromise in optics and speed. The afore mentioned shoot at the religious service would not have been possible if I had had to switch lenses or to use a lens without image stabilization. I would highly recommend the product for someone with a DX format digital SLR who wants the option of not having to swap lenses over a very wide range of subjects and can put up with the necessary compromises that a lens with such a large focal range engenders.
Recommended:
Yes
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Reviews written: 14
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