While I am quite happy with my 21-40-70-105mm prime set, some days a zoom fits best. Those are days when the image isn't known until it's known, or lens changes aren't what I choose to do - lazy days, I guess. Even so, just tossing any lens on the camera isn't the answer either; too much lost quality or light grasp isn't a good thing! So I'd been looking over the midrange options, and wondering...
The ~28-70mm lens range has been popular for decades, especially in the film days. With aps-c it's more like 40-100 which is not much for wide angle, but for urban shooting I haven't found much need to go wide and pull in power lines, traffic and such. Most of the lenses in this range are either indifferent or built for full-frame digital at f/2.8 throughout, and those are heavy and expensive - not what I'm seeking right now, but a nice idea. Choices would be the Sigma 28-70 (replaced by the 24-70), the Tamron 28-75 and little else. Looking into older models I find things like I already have, the Quantaray/Sigma 28-90mm macro - nice but f/3.5-5.6 which is OK but not great. Anything else?
Hmm, Sigma once made a 28-70mm f/2.8-4.0 in both manual (UC) and autofocus (DG). The lens looks pleasantly small, though reviews are rather mixed - especially for the UC model. I found one online and put in a fair bid for the Quantaray variant, thinking DG - but I confused a screw-head with the AF drive pin, so in fact I bid a bit high for the UC model. The price didn't go that high, so for $35 I picked up an indifferent lens that was bound to fall short of my 28-90. Drat.
Drat? Hmm first tests look quite good in fact! The K-5ii does not drop from f/2.8 in the readout screen, but blank-wall tests show this is f/2.8 to nearly 40mm, f/3.2 to 50mm - much better than I expected and substantially faster than the 28-90. Yes it's manual focus but with a bright lens that's not a huge deal, and leaving AF enabled allows the AF points to light up when I get to focus. So much for regret: another $35 bargain lens joins the collection, and the DA21 plus this will cover a lot of focal length!