Mamiya Mamiya-Sekor C 45mm f/2.8

Stopped down to f/8 the center and mid-frame snap into focus and stay there, which is why landscape shooters reached for this one on the 645 bodies. The extreme corners are a different story. They tighten up as you close down but never quite catch the middle, and against a lens built to cover a larger format the edge softness shows. The 45mm covers roughly the angle a 28mm gives on 35mm, so it is the wide-normal of the system, not a dramatic wide. Contrast is moderate rather than punchy, the older Sekor signature, and that suits color negative work where you want shadow detail to survive instead of getting crushed.

Wide open at f/2.8 the edges go soft and the corners smear, normal behavior for a retrofocus wide that has to clear the mirror box on a medium format body. By f/5.6 the frame pulls together and f/8 to f/11 is the sweet spot for everything but the last few millimeters of corner. Field curvature is mild and well controlled for the class. Flare is the weak spot. The C is single-coated by modern standards, so it will still veil and throw the occasional ghost when you shoot into the sun or a bright window. Later revisions tightened up the coatings and handle backlight better. Either way a proper hood is not optional. Use the 77mm thread for a screw-in shade if the bayonet one is long gone.

Bokeh is not really the point at this focal length on this format, but the rendering behind a close subject is smooth and unfussy, no nervous edges or onion rings. People shot environmental portraits with it, the kind where you want the room in the frame and the person grounded in it. For headshots you would reach for the 80mm or the 110mm instead. Architecture, interiors, landscape, documentary: that is where the wider angle and the deep field do the work, not subject isolation.

Who buys it now is someone building a Mamiya 645 kit without paying Hasselblad money. It gets cross-shopped against the Pentax 67 45mm and the Hasselblad Distagons, and it usually wins on cost. The 645 system never carried the Hasselblad cachet, which is exactly why clean glass stays cheap. A good C copy resolves plenty for a wall-sized print, and if you find a later revision for not much more, the better corners and flare control are worth the bump.

One metering note. This is a focal plane body lens with no leaf shutter, so flash sync tops out around 1/60 like any 645 with a cloth or metal curtain. There is no in-lens shutter for the fast sync the leaf-shutter Mamiya lenses give you. Meter it like any normal wide. In a dim interior, meter wide open in Zone Light Meter to confirm your exposure, then stop down to your taken aperture. The 77mm front is the number to remember when you buy ND or graduated filters, and you will want them for the bright skies this wide-normal pulls into the frame.