The "mm" on the lens designation would probably, in my estimation at least, be the result of a marketing dictate rather than a design change. In other words, if Pentax were the last to start using "mm", it might have been "advice" from marketing that resulted in the change.
With respect to the coatings difference, is one more similar to "M" (later, newer) lenses, having the brownish cast? Is that the one with "MM"? CRB - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
