Congratulations on the Pentax 645 purchase!
There are some nice, non Pentax lenses out there that can be adapted to the 645 mount. Loads of Pentacon Six (P6) mount lenses out there, although finding a good adapter is a bit of a chore. Some nice ones to consider are the CZJ 180mm f/2.8 and 120mm f/2.8 - focal length and/or apertures not found within the 645 series of lenses.
For your 645 body (if you decide to go with manual focus glass) - try an eyepiece magnifier (flips out of the way) as well as a split image focusing screen for easier manual focusing.
Pentax 645 UB-21 Split Image Matte focusing screen
or
Pentax 645 UC-21 Split-Image Microprism Matte focusing screen
Originally posted by straightshooter
I've been shooting 35mm for 40 years and digital (K100D, K10D) for 3 years but I just pulled the trigger on my first medium format. I ordered a 645 graded EX with the 75mm lens and a 220 back from KEH. Any of you veteran 645 users have any tricks, tips or suggestions about this camera to share? Thanks.
CW