The Pentax 100mm Macro looks like an old-school lens, with its lockable aperture ring at the back and a huge 'clamp' switch on the side, for locking focus.
Autofocus itself is hit and miss, with a noisy motor drive, punctuated by the clack of the mechanism banging into the end stops at either end of its 0.3-metre-to-infinity range, and there's no focus limit facility either.
As well as this unpleasantness, we experienced a higher degree of hunting during autofocus than with most other lenses in its class.
Optically, the Pentax was soft when shooting wide-open, and we had to stop down to f/8 or f/11 to get the sharpness that we got with other macros at f/2.8. The lens hood is a waste of time, as the inner barrel extends to its front edge at closest focus.