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This lens is a great upgrade to the kit lens, the 18-55 f3.5-5.6, and has a similar topline - slightly wider and quite a bit less telephoto, which is a shame, as the 45mm (67.5mm equivalent) just doesn't feel quite long enough for a standard zoom - for example, portraits are a little too wide or else you get unflattering widening of features if you fill the frame.
The lens feels reasonably well built, slightly dry feeling zoom ring and focus ring which make small adjustments a little tricky, and the lens is quite light which gives it a slightly cheap feel when compared with Pentax's DA* lenses.
As a general purpose lens with an emphasis on capturing a little more of a scene in wides, this lens is great, and image quality is a substantial step up from the kit lens. Aberrations are ok, on larger prints or crops you'll see quite a bit of sharpness fall off and curvature and chromatic aberration, particularly at 16mm and wider apertures.
The motor drive autofocus is quite fast, but noisy, and the quick shift function is useful as you can get the lens in the right ballpark then let the camera's autofocus tweak it for tricky subjects.
Compared to the alternatives, Pentax's own DA* 16-50mm f2.8 and DA 17-70mm f4, the older 16-45mm f4 is much cheaper and for a more modest telephoto end gives you that slightly punchier wide angle. The 16-50mm also has SDM autofocus, which is quieter but has been associated with failure issues.
The Pentax interchangeable lens system provides a complete line of high-quality lenses to satisfy your every creative need. Offering a wide range of focal lengths, functions and effects for different formats, Pentax lenses are designed to maximize each camera's capabilities.