Design and build quality

Pictured below from left to right are the Sigma, Nikkor and Tamron 18-200mm lenses in their shortest positions. Each lens measures 70x78mm, 77x97mm and 73x84mm (diameter x length) respectively. The Sigma's clearly the smallest of the group, although the Tamron is only slightly larger; the Nikkor is comfortably bigger than either of them.



When zoomed-in to their longest focal lengths, the Sigma, Nikkor and Tamron lenses extend by a further 53, 65 and 66mm respectively, each employing two barrel sections. As pictured below, the Sigma remains the smallest of the three and the Nikkor comfortably the largest. The Nikkor's size is reflected in its 72mm filter thread, which is considerably greater than the 62mm threads of the Sigma and Tamron.



Weighing just 405g, the Sigma's the lightest of the group, although the Tamron's only 18g heavier; at 560g the Nikkor's noticeably heavier than either. The Nikkor's additional weight is undoubtedly down to its superior build quality and slightly faster optical performance at the telephoto end. It sports a focal ratio of f3.5~5.6, compared to the f3.5~6.3 of the Sigma and Tamron models.

In terms of build quality, the Sigma and Tamron are roughly similar. They're both lightweight budget lenses so unsurprisingly feel quite plasticky with less smooth mechanics than a premium product. Don't get us wrong, they're not poorly constructed, but are clearly below the build quality of more expensive lenses.

For example, you need only compare them with the Nikkor 18-200mm to immediately notice how this pricier model looks and feels to a much higher standard. It's more solid with smoother mechanics delivering a greater impression of confidence in use. Of course the Nikkor costs twice as much, but if you're after the best build quality, you'll need to spend the extra.

We're pleased to report all three employ internal focusing with non-rotating end sections - important for anyone who uses polarisers, although obviously the Nikkor's wider thread will incur higher-priced filters. Thankfully, all three lenses were supplied with hoods.

In terms of focusing speed, the Nikkor's premium SWM system was certainly quicker than the Sigma and Tamron, but not by a large degree. Where they really differed though was in focusing noise with both the Sigma and Tamron models being considerably louder than the Nikkor. The Tamron was worst of all in this respect, grinding quite conspicuously during manually focusing. Again if ultimate discretion is your thing, you'll need to spend more on the Nikkor.