Conclusion - Pros
- Huge 13.9x focal length range, ideal general purpose and travel lens
- Good image quality in the wide to short telephoto range
- Fast, quiet autofocus
- Low distortion (for a superzoom)
- Good build quality, smooth zooming action and no zoom creep
Conclusion - Cons
- Very inconsistent sharpness through the zoom range - extremely soft at 135mm
- Soft corners at almost all focal lengths
- Image stabilization not as effective as on similar lenses, especially at telephoto end
The Sigma 18-250mm F3.5-6.3 DC OS HSM, perhaps unsurprisingly, seems very much to be a case of 'take the 18-200mm OS, make it longer', and exhibits much the same characteristics as the older design. It's therefore a lens which takes a slightly different approach than usual to the 'all-in-one' superzoom concept, trading off absolute sharpness against other desirable optical characteristics, namely relatively low distortion and chromatic aberration. So, just as we noted with the 18-200mm, if you're the kind of photographer who absolutely demands pixel-level sharpness in your images, you can look away now - this simply isn't the lens for you. However, if you don't tend to examine your pictures in that level of detail, and want straight lines to appear as nearly straight as possible, the 18-250mm becomes well worthy of consideration.
In terms of operation and ergonomics, the 18-250mm scores pretty highly. The HSM autofocus is fast, silent and positive, and probably on a par with Canon and Nikon's own image stabilized superzooms - this is important when you want to grab quick shots of moving subjects. The zoom action is impressively smooth and even in feel for a lens with such a long range, and our sample also showed no inclination towards zoom creep (i.e. the tendency for the zoom mechanism to extend under its own weight), which is a common affliction of superzoom designs. Of course that enormous zoom range is compelling in itself - and hugely useful in situations when changing lenses is undesirable or inconvenient.
The optical stabilization system, however, is some way short of the best we've used, and perhaps the weakest link of the package. It works reasonably well towards the wide end, giving about three stops benefit, but disappointingly is at its least effective at telephoto, where we got at best two stops stabilization (compared to 4 stops from the best performers in this class). This is problematic because it's where you need it most; indeed the combination of the long focal length, slow F6.3 maximum aperture, and ineffective OS means that on anything other than a bright, sunny day, you'll find yourself struggling for light, and needing to boost the ISO significantly to get usable results.
Many potential buyers will of course be interested in how the Sigma compares to its most obvious direct rival, the Tamron 18-270mm F3.5-6.3 Di-II VC. As usual, the answer to this question is not entirely simple, with the two lenses having a different array of strengths and weaknesses. In a fashion that's almost stereotypical between the two brands, the Tamron certainly appears to be consistently sharper, and has a rather more effective stabilisation system. The Sigma, in contrast, has arguably a more balanced overall design approach; alongside its low distortion, the autofocus is far faster and quieter, and the build quality and ergonomics are better too.
Ultimately, with superzooms, the choice comes down to a game of 'pick your favorite compromise', as there's inevitably a penalty to be paid for the undeniable convenience of carrying around such a large zoom range in a single lens. If you tend to share your pictures by posting downsized versions to photo-sharing websites, or making small prints to show around friends and family, the 18-250mm's relative lack of sharpness won't be much of a problem, and its low distortion will be a positive virtue. Likewise if you're after an all-in-one travel lens, and want to be able to grab quick snaps of friends or children, that HSM autofocus system may well prove to be beneficial. As always, the choice is yours.
Rating (out of 10)
|Ergonomics & handling||8.0|
Recommended (with reservations)
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Sigma 18-250mm DC OS HSM Review Samples