Sigma 18-250mm f/3.5-6.3 DC OS HSM - £400/ $480
Like Sigma's 18-200mm, this is a 'DC' lens for APS-C-format cameras. Both lenses have Sigma's four- stop OS (Optical Stabilisation), and HSM (Hyper Sonic Motor) autofocus. Unlike many of the brand's more exotic lenses, the 18-250mm doesn't have advanced ring-type HSM, but the motor-driven system is still fairly speedy and quiet.
It's bigger than the 18-200mm, but it's easier not to foul the the focus ring's action while it's rotating. You get a lot more reach at the telephoto end, equivalent to 375mm. However, the maximum available aperture of f/6.3 means the image stabilisation has its work cut out in anything other than bright, sunny conditions.
Performance
Sharpness is adequate at wide- angle and mid-range zooms, on a par with the 18-200mm lens, but there's a drop at the longest end of the range. Fringing can also be noticeable as you approach the 250mm focal length. But distortions are well controlled considering the extra-large zoom range.
Sharpness
Sharpness is in line with the Sigma 18-200mm's at wide-angle to middle focal lengths, but drops off at 250mm.
Lab test at f/8
Sharpness at wide angle: 1449
Sharpness at mid range: 1165
Sharpness at telephoto: 1019
Fringing
Most noticeable at either end of the zoom range. There's still some apparent colour fringing around the 135mm mark.
Lab test at f/8
Fringing at wide angle: 1.25
Fringing at mid range: 0.98
Fringing at telephoto: 2.18
Distortion
Given the generous zoom, distortions are fairly low, especially for pin-cushion distortion at telephoto settings.
Lab test at f/8
Distortion at wide angle: -2.48
Distortion at mid range: 1.02
Distortion at telephoto: 0.84
Image quality verdict
Outright sharpness could be better, especially towards corners of the frame, but the Sigma 18-250mm acquits itself fairly well overall.
Taken at 18mm (min)
Taken at 250mm (max)
