Originally posted by prohtex I became accustomed to with Rodenstock and Schneider 4x5 lenses.
I work with 4X5,5X7 and 8X10 formats so I know where you are coming from.
Originally posted by prohtex I understand that Pentax started releasing “DFA” lenses around the time the 645D came out. Can anyone explain the difference between a “D” and a non-“D” model lens?
Perhaps the biggest operational difference is the lack of an aperture ring on the DA and D-FA lenses. Optically the DA lenses are supposedly optimized for a highly reflective imaging sensor, with coatings to reduce ghosting that would not occur with film.Optically, Pentax DA lenses have a smaller imaging circle than FA or D-FA lenses, this is an optimization that supposedly makes wider lenses lighter. The only two 645 lenses that I can think of that has made use of such optimization are the Pentax DA 645 25mm f/4 AL (IF) SDM AW* and the HD PENTAX-DA645 28-45mm f/4.5 ED AW SR lens**. DA optimizations only really have an appreciable effect on wide angle lenses, longer focal lengths are going to be large and heavy regardless of the format.
Originally posted by prohtex I were to trade my older 150mm lens purchased on eBay (that was likely manufactured sometime in the past 10 years) for this newer model, am I likely to see any improvement in sharpness?
Most likely, a complete optical re-design of this lens with aspherical elements and ED glass would no doubt improve image quality substantially. Optical coatings haven't changed much over the years, Aero bright, ghostless coatings and physically protective coatings are the latest advances from pentax - these additions would in all probability provide a modest improvement in contrast and flare handling characteristics.
* This lens is discontinued according to B&H. The full format compatible Pentax D-FA 645 25mm f/4 AL (IF) SDM AW ultra wideangle lens, AFAIK is still available on Japanese markets, and it performs superbly on film.
** though this optimization doesn't prevent this lens from being a complete brick of a lens.