Guy Wrote --->"How many dedicated digital lenses are made for the Pentax 2 or 3 than you have to rely on on lenses built for film."<<<
Guy, my comments here only reflect upon the Pentax Medium Format lenses used on the 645D body and in no way comments on your statements regarding other capable medium format systems. For approx. the last 9 months, I've been testing multiple samples of virtually every Pentax AF 645 lens made, on the 645D body. I haven't yet posted these comprehensive results. What I can say, for better or worse that with regards to the digital specific lenses Pentax has released for the 645D (all two of them), that optically they are no better and in fact in some performance related areas, worse than many of their (Pentax's) film era AF 645 lenses....many of which have notable performance by most critera. So I'm not sure in this particular case that digital specific designed lenses have a unique advantage...at least not yet with regards to their use on Pentax's 645D. Time will tell when future lenses are released by them.
No doubt with other manufacturers, both medium format and 35mm, that many of the latest digital specific lenses, clearly outperform their film era counterparts. I've seen this most certainly with the 35mm DSLR systems I've shot with, in making lens comparisons and choices. So the Pentax MF system as it is today represents a good value and offers a tremedously wide variety of focal length lenses..both fixed focal length and zooms. Many of these legacy lenses may not be readily available as new, especially here in the states...but most are fairly plentifull on the used market in most all types of conditions and for what some would consider reasonable cost. In fact some are downright inexpensive when compared to other manufacturer's MF lenses. In this regard it's more of a complete system than it initially appears to some, although I'd be the 1st to agree that not all lenses take full advanatage of what the 645D sensor may be capable of. If and when Pentax releases a host of digital specific lenses and they clearly offer clear advanatges over their film era counterparts (other than weather resistance), then my assessment of this system would certainly change.
Aside from the digital specific 25mm (effective 19.5mm) and 55mm (effective 43mm) MF 645 Pentax lenses...Pentax's Af MF 645 lenses also include focal lengths of 35, 45, 55, 75, 120 macro, 150, 200, 300 (two different ones), 400, 33-55, 45-85, 55-110, 80-160, 100-300 and some others I left out...and these are all 645 autofocus lenses! Just multiply these focal lengths by 0.8 to get their effective focal length on the 645D body. There are also manual focus 1.4 and 2x teleconverters, new focusing screens, PTTL flashes and more. Maybe not the most complete MF digital system nor capable as some others...but the point is more complete than most are aware of. Of course as pointed out, Pentax can't rely on the past and in order to compete, must be both innovative and competitive with future lens releases, especially those that offer a higher level of performance. Lastly as Guy and others have pointed out...Pentax has to make these lenses available new on the current market, to truly make it a viable system. Some can't rely on looking on the used market for a specific lens, especially if they are a working pro and need a particular lens, "now"!
Dave (D&A)