The 645n handles much like a big SLR. Noisier, of course. I'm not sure whether its heavier than a Nikon F series with a motor drive, etc. The motor gives the 645 about 1.5 frames per second. Ken Rockwell has a laudatory writeup:
Pentax 645N Ken's prices are sadly out of date.
Pentax Photography & Camera Forum - PentaxForums.com has user reviews of the 645 line. There are three, the 645, 645n which I own, and the 645nii, which adds mirror lockup, considered by The Luminous Landscape, to be unnecessary. The ii is also rarer and much more expensive.
The 645 is menu driven, the 645n and nii aren't. Hoorah! Ken Rockwell's site discusses both the 645 and 645n.
Film inserts rather than magazines are used; no switching mid roll. They come in both 120 and 220 capacities; one can be converted to the other in a few minutes with a jeweler's screwdriver to remove one screw and reverse a plastic piece.
I have only the manual focus lenses; they have a wonderful feel and are all metal, the way God intended lenses to be. A word of warning: since the 645d, the digital model, came out the market has gone wild for 645 lenses since the digital model can use the same lenses. For example a 35mm new old stock (the box even had the warranty card!) for which I paid $550 earlier this year now goes for $1100 or more in used, E condition. Good grief!
The longest lens readily available is a 200mm, not very long. Lenses from the Pentax 67 can be used via an expensive, uncommon Pentax adaptor with full automation. Cheaper adaptors don't give auto diaphragm. Lenses up to I think 600mm were available for the 645, rare and hideously expensive. Pentax 67 lenses range up to I think 800mm - good grief - and are also expensive. Some 67 lenses vignette used on a 645. There ain't no free lunch.
My kit includes the 75mm normal, the 55mm wide angle, the 35mm wide angle, the 120mm macro (continuous focusing to 1 to 1) and the 200mm tele. I also acquired the extention tubes, and the right angle finder. This latter is wonderful for low level shots on a camera with a fixed pentaprism. BTW the camera has two tripod sockets so with two quick release plates going from horizontal to vertical is quick and re-framing isn't needed. A minor stroke of genius in my view.
My whole kit fits into a Lowe MiniTrekker. Very portable but getting a bit heavy. For walk-around I go with the 75 or the 55; not too heavy a load. YMMV, of course.
