The FA 45-85mm is a fine lens, it's one of my most heavily used options for landscapes (critical sharpness with manual focus) and general walking around (convenience with accurate autofocus). I found it definitely better than the FA 45mm prime @ 45mm. And I had a new DFA 55mm but took it back; it wasn't there in the corners compared to the 45-85mm, especially for the money involved. The 45-85mm is generally good throughout the focal range. If I was to blue-sky things a bit, I'd wish the 45-85mm was a bit lighter perhaps, and a stop faster.

But other than that a good copy of the lens would be a fine addition to cover the standard focal range, in my opinion.
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SMC Pentax-FA 645 45-85mm F4.5 Reviews - 645 Zoom Lenses - Pentax Lens Reviews & Lens Database