Noticeably larger and about one-and a-half times heavier than the SMC Pentax DA 18-55mm f3.5-5.6 AL WR kit lens, the 16-45mm gives you better wide-angle coverage. The flip side is that you lose telephoto reach, with a maximum effective focal length of 67.5mm.
Build quality isn't noticeably better than with the 18-55mm kit lens. It also lacks the cheaper lens' newly designed WR (Weather Resistant) construction.
What you do get is a constant maximum aperture throughout the zoom range, although, again, it's a relatively slow f/4 compared with the f/2.8 of other constant-aperture lenses.
Handling is good with smoothly operating zoom and focus rings, the latter enabling full-time manual override once autofocus has been achieved. There's no built-in autofocus motor, so AF is driven from the camera.
Autofocus speed is fast, but quite noisy. Vignetting is noticeable when shooting at 16mm with the maximum f/4 aperture, but is quite restrained at all other zoom and aperture settings.
The main bugbear is that barrel distortion is quite pronounced at the wide-angle end of the zoom range. However, that isn't bad news for most Pentax users, as recent cameras including the K-x, K-r, K-7 and K-5 all feature automatic, in-camera lens corrections for both distortion and lateral chromatic aberration, making this lens a bargain.
Despite lacking an internal autofocus motor, Pentax's Quick-Shift system enables full-time manual override after autofocus has been achieved. It's not unique though – the 18-55mm kit lens has this feature too.
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