Pentax SMC DA* 16-50mm f2.8 ED AL (IF) SDM Review

One attraction is that constant f2.8 lens aperture, which makes manual exposure adjustments easier (no need to allow for different available apertures and different focal lengths) and it allows better low-light shooting at longer focal lengths. In fact, at 50mm, this lens has a two-stop aperture advantage over a regular kit zoom. Another is the zoom range – it’s a little shorter than the average kit zoom at the long end, but usefully wider at the short end, where it’s roughly equivalent to a 24mm lens rather than the usual 28mm.

This lens also incorporates Pentax’s SDM autofocus motors, which are much smoother and quieter. Having said that, there is still some slight hesitancy with some subjects which you don’t get with Nikon or Canon cameras, say. This is more likely to be the camera and its AF sensor rather than the lens, though.

One of the principal reasons for choosing a lens like this, though, is improved optical quality, and the Pentax 16-50mm certainly delivers this, though it’s by no means perfect. There’s some fairly pronounced distortion at the 16mm end of the range, coupled with a degree of chromatic aberration. And while the definition is good at short-medium focal lengths even when the lens is wide open, it’s not quite so good at 50mm, where you need to stop down to around f5.6 or beyond to get the best results.

Realistically, you’ve got to expect some limitations, even in a premium fixed-aperture zoom like this one, and the fact is that the Pentax 16-50mm f2.8 does very well for its price. The equivalent Canon and Nikon lenses cost twice as much as this one but are no better optically and, in fact, might struggle to match this lens’s full-aperture performance and consistency across the focal range, overall.

Choosing a better ‘standard’ zoom for Pentax D-SLRs is a bit of a juggling act. There’s also a pretty good 17-70mm f4, which has a wider range than this one and costs less. But if you want to shoot in low light and get the best possible results across a range of focal lengths and apertures, this 16-50mm is almost certainly the best of the bunch.