Mamiya RB67 KL 150mm f/3.5 L

Although not breathlessly sharp, this is a good, solid performer, perfect for use with a 645 back. In its place, you might consider a 140/4.5 macro which is better corrected for close-up work.

A very good, compact, light weight lens; a natural for a 645 back.

Nothing obvious, though a 140/4.5 macro would seem like a good substitute.

90mm, 127mm, 140mm, 180mm, 250mm.

Best in the business.