There's been some interest in the forum about how well the FA 35mm f/3.5 works on the 645D. I got a new copy of the lens quite awhile back for use on my Canon digital bodies with a Zoerk PSA adapter. I haven't shot the lens much on my 645D yet, since ironically it has been a bit wider field of view than I've usually needed in what I've been photographing so far.
I did get a chance to use it a little bit last weekend out in the Canadian Rockies. Attached here is a down-sampled frame from several I took. If anyone is interested in seeing the full size image, please email or PM me and I will provide you a link to a full resolution JPEG, for personal use only. (Please no reproduction.) It's sizable, so I'm not posting the link for the entire world, lest my bandwidth be crushed.
Details of the shot: Mt. Michener, David Thompson Country, Alberta, Canada. Photographed with Pentax 645D, FA 645 35mm f/3.5, f/11, ISO 100, tripod, cable release, manual exposure, autofocus on distant mountain peak. Converted from DNG with Adobe Camera Raw 6.3, no sharpening, linear curve, all exposure settings neutralized except for slight recovery slider for highlights.
Since I haven't processed the image, it looks quite flat, and the midtones are underexposed since I was preserving the distant snow highlights. Detail is good in general, however, and the image processes up very nicely and looks great for the most part. (I did sharpen the small image for posting here, but the full resolution image is unsharpened.)
However there is one significant negative characteristic that I'm seeing in the few files I shot -- some mustache pattern distortion equally spaced towards the outer edges on the left and right. I'll need to do a few more controlled test shots to confirm whether that's really what's going on, but if it is then it's quite problematic since that kind of thing is very difficult to compensate for. There are many situations where it wouldn't be a factor, but in landscapes it would be troublesome.