I'm not sure I buy that argument about only using Pentax glass. I am a firm
believer that it's very difficult to go wrong with Pentax glass, but there
are gems out there from other manufacturers that are as good, better or at
least more useful to a particular photographer than a similar Pentax
offering. This is especially true in the world of Macro lenses where almost
every lens made is exceptional. The Tokina, Tamron and Vivitar 90s are good
examples. The Kiron 105 is another. Outside of these lenses, The Tokina
100-300F4 AT-X comes to mind as superior to any equivalent offering from
Pentax. You have to remember, these companies are in the business of building
lenses. They have some of the finest engineers. I would not overlook these
lenses if they help you get the job done.
Vic
