Mamiya Sekor C 45mm f/2.8 N/L

On a Mamiya 645 the 45mm is the lens that never comes off when the room is small and you cannot make it bigger. Cramped interiors, a reception in a low-ceilinged hall, a bride getting ready in a hotel room you can barely turn around in. On the 6x4.5 frame this is your moderate wide, roughly a 28mm equivalent in 35mm terms, wide enough to take in a room or a foreground but not so wide that faces near the edges go funhouse. A 35mm makes the room look big and the people look small. The 80mm normal makes you back into a wall you cannot back into. The 45mm threads that needle.

Optically it is a retrofocus design, which it has to be to clear the mirror box on the focal-plane 645 bodies. Wide open at f/2.8 the center is already crisp and the corners lag, the usual story for a fast medium-format wide. Stop down to f/8 or f/11 and the whole frame snaps into edge-to-edge bite. Contrast sits on the higher, more modern side compared to the older non-N Sekors. The "N" generation got better coatings and flare control, so you can work closer to a window or a bare bulb without the image going milky, though a stray sun in the frame will still throw a veil. Color rendering is neutral and clean, no vintage warmth to lean on.

This is a landscape and environmental-portrait tool more than a bokeh lens. f/2.8 on this format does give you real subject separation, and the out-of-focus rendering is smooth without being a personality, but nobody buys a 45mm wide to melt backgrounds. They buy it to keep the church, the field, the whole scene sharp and present behind the subject. Documentary and wedding shooters who run 645 for the bigger negative and faster handling than 6x7 lean on this focal length hard.

The honest weakness is distortion. It is a wide retrofocus, so you get visible barrel distortion that shows up the moment you put a horizon or a doorframe near the edge. For architecture you will be correcting it in post or composing around it. The other catch is that this is a manual-focus, focal-plane lens with no leaf shutter, so flash sync tops out at the body's curtain speed (1/60 on most 645 bodies). If you shoot fill flash outdoors at wide apertures, that ceiling matters.

Today these go for reasonable money next to the equivalent Pentax 67 or Hasselblad glass, and that gap is most of why people pick the 645 system in the first place. They cross-shop it against the 35mm f/3.5 (wider, slower) and usually decide the 45mm is the more usable everyday width. The 67mm filter thread is shared across several Mamiya lenses, so one set of NDs and grads covers your kit. When you do stack filters for a long landscape exposure, set the threads and your factor in Zone Light Meter so the metered time already folds in the filter loss before you trip the shutter.