Lens review

Sigma 18-200 mm f/3.5-6.3 DC OS

8. Vignetting

Megazooms never perform well in the vignetting category. The Sigma 18-200 mm OS is not an exception here, especially at 18 mm, where, wide open, we deal with the light fall-off in the frame corners amounting to as much as 35% (-1.25 EV). On stopping down to f/4.0 the situation improves just slightly because the vignetting decreases to 28%. Only by f/5.6 aperture we can see the problem decrease to an imperceptible level (14%) and we won’t have any problems with this aberration by f/8.0.

A significantly better situation can be observed at 50 mm. By f/5.0 the brightness loss in the corners amounts to 17% and it decreases to just 10% by f/5.6. When we increase the focal length to 100 mm the vignetting starts increasing again – by f/5.6 the measured level of this aberration reaches 20% and by f/8.0 – a negligible value of 6%.

Huge problems return at the maximum aperture where by f/6.3 the vignetting amounts to 27% (-0.91 EV). Fortunately by f/8.0 the level of this aberration decreases to 13% and by f/11 it reaches an imperceptible level of 5%.

Although these results are nothing to boast about once again against the background of its competitors the Sigma shouldn’t be ashamed of them either. At 18 mm the rival lenses record a vignetting level of 36-43%. Toward the long end the Sigma’s result is of the same order as other lenses with similar parameters.