Sigma 18-200mm f/3.5-6.3 II DC OS HSM - £420/ $500
The recently launched version of this lens is smaller and lighter than its predecessor, at 75 x 88mm and 490g rather than 79 x 100mm and 610g. The filter size has been reduced from 72mm to 62mm, too. The new lens also gains an FLD (F Low Dispersion) element. This is equivalent to top-quality fluorite glass, giving high light transmission and very low dispersion. Even so, the largest aperture at the telephoto end is still a sluggish f/6.3.
The first-generation Sigma OS from the original lens has been updated, taking performance from 2.5 stops to four.
Performance
Autofocus is fast and quiet, but it's driven by an ultrasonic motor and the focus ring rotates during autofocus. Sharpness isn't as good as with Nikon lenses at wide-angle and mid-zoom settings, but instead of dropping off at maximum telephoto focal lengths it increases a little. The Sigma has the sharpest performance of any lens in the group at its maximum zoom stretch.
Sharpness
Fairly consistent throughout the zoom range, sharpness is okay at the centre of the frame, less so towards the corners.
Lab test at f/8
Sharpness at wide angle: 1461
Sharpness at mid range: 1194
Sharpness at telephoto: 1218
Fringing
Apparent at both ends of the zoom range, fringing at image corners can also be noticeable at mid-range settings.
Lab test at f/8
Fringing at wide angle: 1.67
Fringing at mid range: 0.77
Fringing at telephoto: 1.58
Distortion
Barrel distortion at 18mm is more obvious than with the Sigma 18-250mm, despite this lens's smaller zoom range.
Lab test at f/8
Distortion at wide angle: -3.26
Distortion at mid range: 1.11
Distortion at telephoto: 1.11
Image quality verdict
Edge-to-edge sharpness could be better, especially when you're using the largest available apertures. Overall, this lens is good rather than great.
Taken at 18mm (min)
Taken at 200mm (max)
