Sigma 18-200mm f/3.5-6.3 DC OS HSM review

The 18-200mm F3.5-6.3 DC OS HSM is on the face of it an ideal 'do-it-all' travel lens; the 11x zoom range, image stabilization and useful close focus distance combine to give great operational flexibility. But of course this versatility comes at a cost, as optical compromises must necessarily be made to provide such a long range in a single lens. And Sigma's designers appear to have chosen a set of compromises somewhat different to those made in competing lenses, giving their 18-200mm its own character and attributes.

Most interestingly, this is a lens which appears to concentrate on minimizing distortion and chromatic aberration rather than maximizing sharpness. This immediately means it won't win the favor of a certain type of resolution-obsessed photographer, who will look on its inconsistent sharpness (and indeed substantial lack of it at mid-telephoto focal lengths) with displeasure. But for users with less lofty aims - perhaps making ordinary postcard-sized prints, sharing reduced-size versions of their pictures on the internet, or viewing their images on the computer or TV screen without zooming in to scrutinize every minute detail - it's sharp enough, and for such purposes its virtues of relatively low distortion and chromatic aberration will shine through. In this regard it's important to realize that certain lens attributes - severe barrel distortion at wideangle, for example - have the same negative impact on a print whether it's 6" x 4" or 36" x 24", and that high levels of co lour fringing can have a negative impact at print sizes smaller than those needed to reveal those lower levels of sharpness. So Sigma's approach will potentially pay dividends for the casual vacation photographer looking to use the images straight out the camera with no post-processing.


Andy Westlake

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