Kiron 28-105mm f3.2-4.5. Picked this lens up for next to nothing the other day and I'm pleasantly surprised - nice and metal and heavy, already good wide open (as here) and very sharp stopped down to f8. Has some of that 3D feel to it that we all crave. Fringing is well controlled and when it does occur it's a rich, royal blue - I've never seen a fringing colour like it before!
Like many old zooms it has a close focus function, but unusually in this case it is at the wide end, meaning you really have to get up close and personal with your subject in order to get your shot. Focuses down to 1:4 though, which is pretty good for a lens of this type and certainly enough to isolate the average flower.
This photo was taken on the K-7, ISO 200, 105mm at f4.5