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Field Test: Sigma 18-250mm f/3.5-6.3 DC USM OS Lens
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Field Test: Sigma 18-250mm f/3.5-6.3 DC USM OS Lens

What can't this lens do?

Optical advances make now a great time to get a long-range zoom lens.


Sigma 18-250mm f/3.5-6.3 DC USM OS Lens Specs


Zoom range: 18-250mm
Apertures:
Minimum f/3.5-6.3
    Maximum f/22-40
Filter Size: 72mm
Optical Stabilization: Yes (on-off switch)
Weight: 22.2 oz.
Length: 4 inches at 28mm

 

 

 

Executive Summary

With the advent of smaller digital sensors in DSLR cameras and computer-aided optical engineering advances, lens designers are able to squeeze longer focal ranges into moderate-sized lenses, creating a new and growing category, the superzoom DSLR lens. Sigma’s 18-250mm is one of the latest to enter this field, and it promises the kind of one-lens-does-it-all flexibility that will appeal to many DSLR photographers.

The 18-250mm f/3.5-6.3 DC OS HSM lens will be available in Nikon, Canon EOS, Pentax, Sony/Maxxum, and Sigma camera mounts, and can only be used with cameras that have APS-C format sensors. At the time of this writing, it is expected to sell for $530.

 

I had the opportunity recently to take the Sigma 18-250mm out into the field, mounted on my Canon 20D, and put it through its paces.


Yes, you can shoot portraits with it: The Sigma 18-250mm delivered a sharp portrait of my daughter at 250mm.


In the field, a macro surprise


While of course the 18-250mm zoom range is impressive, one of this lens’s strengths is its close-focusing abilities: The minimum focus mark on the lens barrel (and in the lens’s specs) is 1.48 feet, but in the field, I was able to easily focus much closer than that. The lens actually focused to approximately five inches from the front of the lens at all focal lengths—not just at the wide-anglesetting—giving near-macro performance at 250mm. The lens barrel is marked with a top magnification of 1:3.4, and this is much more accurate than the focus markings indicate.

Holy macro: Focused at around five inches from the front of the lens, I was able to get fairly close here at 18mm, but look at what happens when zoomed all the way out to 250mm…

At 250mm, close focus remains unchanged! Still focused on a subject approximately five inches from the front of the lens, the 18-250mm delivered 1:34 magnification. Hand-held at 1/100 sec, OS helped keep it sharp.

The lens could be useful when photographing sporting events since you can quickly go from close-ups of the action to sweeping overviews, although getting from one focal extreme to the other takes a bit of exertion; I found its zoom action was a little stiff.

Action freeze: Responsive AF and Optical Stabilization helped me get this action shot at a local park, but quickly zooming from wide to tele took some effort due to tight zoom ring.

Focusing is internal and the HSM motor was fast and quiet. The front element does not rotate, which means you can use polarizer and graduated filters without worry that focusing or zooming will change their orientation. However, be aware that the lens shifts focus as it zooms, so you need to re-focus whenever you change focal lengths, even if camera-to-subject distance remains unchanged—a minor inconvenience.

Field test discoveries

Vignetting:
Best at 50-80mm. Slight vignetting at 18mm. Moderate vignetting at 250mm.

Distortion: Slight pillow distortion at 18 and 28mm, disappears by 50mm. No apparent distortion at any telephoto setting.
 
Flare: Well controlled at all wide-angle settings. Moderate flare at all telephoto settings when shooting directly at strong light source. (Note: Photo at right for illustration only. Conclusions based on standardized test photo.)
 
Focus accuracy: At 100% enlargement equivalent to 16x20 print the lens delivered acceptably sharp images of our “test fence” at all focal lengths.
• At 250mm, focus was sharp in the center of the frame, but fell off in the corners. Corners also showed barely-perceptable fringing.
• At 80mm, focus was very sharp in the center and was moderately sharp in the corners, with no noticeable fringing.
• At 18mm focus was sharp in the center of the frame but fell off in the corners. Corners showed slight fringing.

 


 

Zoom creep: There was no zoom creep, even when the lens was pointing down and gently shaken while at 18mm. A zoom lock seemed unnecessary as it only worked at 18mm.

Conclusion

The Sigma 18-250mm lens is compact, general-purpose lens that offers a wide zoom range, surprisingly close focus, and image quality that should satisfy owners of starter and enthusiast-level DSLRs. It is well-balanced and light, with responsive autofocusing and effective Optical Stabilization, and I found its zoom range to be wonderfully liberating.

 

While there are times when you may want a short-range wide-angle zoom lens (for instance, if you want to be unobtrusive and wish to travel light, or want a lens with a wider aperture), for many DSLR photographers this could become the only lens you’ll need.


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