Originally posted by AyeYo Does the F 28-80 f3.5-4.5 maintain the same rendering or does the additional range ruin it?
A warning: the Takumar-F 28-80 looks exactly like the SMC F 28-80, and is much easier to come by, but it's very much worse than the 35-70 wide open. Very soft and lots of spherical aberration. The SMC has a different optical formula with more elements, which is unusual between Tak-F and SMC F, so hopefully the SMC is better corrected for SA. If you go down this road, make sure you don't get the Takumar by mistake.
If you really want to get to 28mm in a light package, the FA 28-70 F4 AL looks interesting. Plentiful, constant aperture, and super cheap. There aren't too many sample photos out there but what I do see looks like it has some depth and life.
I'm feeling you on the current zoom lineup. The flickr page for the D-FA 24-70 isn't exactly dire, but the portrait images lack pop and three-dimensionality. The DA 16-50 is... let's charitably say not being well-represented by its users.
To my eye, the Tamron 28-75 2.8 looks like it renders three-dimensional objects at portrait distances much more pleasantly than the Pentax-branded options. Not sure if it's on the same level as the Canon, but it's probably what I'd go for if I had to buy new, and it's the cheapest and lightest to boot. I kinda want to buy one now. I've certainly been impressed with my Tammy 70-200.