Which Lens

Don't know about the sigma, but the tamron does suffer from purple fringing in high contrast situations.

To be honest, for the cameras you list I'd get onto ebay and track down something like the old Pentax-M 80-200mm f4.5. This is a brilliant lens, not horribly expensive for a decent example but very sharp and well-made. I have two which are unfortunately in need of attention for a sticky aperture mechanism and some dust/smearing on internal glass respectively. Before the problems developed I had some superb results from the lens. Alternatives could include the Pentax-M 75-150mm f4, Pentax-A 70-210mm f4 or the various 200mm f4 they've made over the years.


Bear in mind that many current Pentax-fit lenses lack an aperture ring as the digital bodies don't need/use one, the ME S and K2 can't control aperture from the body. As a result I'd be inclined to look for SMC Pentax, Pentax-M or Pentax-A lenses, which are still capable of astonishingly good results and are better suited to your cameras.

Edit, if you want 300mm and want a zoom (300mm primes being uncommon and often expensive) then look at the old Pentax-F 100-300mm or the other Pentax zooms of similar range. They won't be as nice to focus manually as they lack the damping of the older lenses, but they do have an aperture ring and will be able to work with your cameras.

I'm not sure that would be the case with film, it may be an issue with the digital sensor more than the lens.

John

I'd concur with what Matt wrote here, but add that the Tamron does have an aperture ring if that's your choice of lens, manual focus will lack damping though and the focus ring is at the front of the lens, a little cumbersome IMHO. The build quality/ergonomics of the early K,M & A series lenses is far better.

John