The Sigma 18-200mm f/3.5-6.3 DC AF is a small lens considering what it
can do. Well, not even considering that. For a zoom, it's a small lens.
About the same size as Nikons 18-55 kit zoom. Construction quality is
about the same, perhaps even a touch worse. Similar in size but double
in weight; Sigma packs some glass into this little plastic package.
Sigma may be the most notorious lens maker for bad quality
control. I think I lucked out and got an exceptional example of their
18-200. This lens does not focus particularly well. In fact it almost
always back focuses at wider angles. I found a method to work around
this problem: zoom in to get focus, then zoom back out to desired
composition. This worked well for about six months. Then zooming out
started dragging the focus, and everything was blurry. After two trips
back to Sigma the problem was never fixed. Getting accurate focus
became a struggle and I stopped using the lens and bought the much more
expensive Nikkor 18-200mm only to find that it had the same issues
(although not to the same extent).
Nick Troutman in Vera Cruz, Mexico.
Nikon D50, Sigma 18-200mm @ 55mm 1/1250 F9 ISO 800
100% crop of the same.
Nikon D50, Sigma 18-200mm @ 55mm
1/1250 F9 ISO 800
Of course the 6mp Nikon D50
is not a demanding camera. The lens doesn't look as good on the 10mp
D200, but still holds its own fairly well.
Nikon D200, Sigma 18-200mm @ 155mm 1/1000 f9 ISO 200
Ah the dreaded Sigma
lower than standard kit
Terrible focusing ring and not the
Modestly sharp from 18-150mm, crippled by poor focusing.
It's cheap at
quality, poor AF and too fragile for whitewater kayaking.
for kayaking: 6/10
With an 11x zoom range it's very versatile. If you baby
your gear and use a Pelican Case instead of a Watershed bag this lens
might work for you. There is a lot of distortion but I don't find
this troubling in kayaking. Architecture would be another story.
It has the worst AF performance I've ever seen, by a long shot.
It's surprisingly sharp from 18-150mm while the 200mm end never
sharpens up and is best ignored. It's light, small and cheap, with a
bit more performance than you might expect; sharp if
you can get it to focus on your
subject. Perhaps the newer version with in lens AF motor and optical
stabilization solves some these problems?