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
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.