Mamiya Mamiya-Sekor C 55mm f/2.8 N/L

High noon, a couple standing in hard sun, and a photographer who wants the sky to go deep blue instead of washing out to white. He sets the leaf shutter to 1/500, fires a strobe through an umbrella, and the 6x4.5 frame comes back with a saturated sky and clean light on their faces at once. That is the whole reason a leaf-shutter 55mm exists. A focal-plane Mamiya 645 body syncs flash around 1/60, which hands the sky back to the sun every time. Move the shutter into the lens and it syncs at every speed it has.

On the 645 negative, 55mm is neither wide nor normal. It works out to around a 34mm equivalent in full-frame terms, the moderate wide that environmental portrait and wedding shooters grab when the 80mm normal is too tight for the room. The focal length sits shorter than the mount's flange distance, so this is a retrofocus design, built out to clear the reflex mirror with the leaf shutter packed into the barrel between the elements.

Optically it behaves the way the rest of the Sekor wides do. Expect the usual retrofocus arc: a little soft and low in contrast wide open, then snapping into proper bite once you stop down a couple of clicks, with the corners closing the gap on the center as you go. Stop it down for a landscape and it covers the big frame cleanly. That mirror clearance does not come free, though, and a retrofocus wide of this vintage tends to carry some barrel distortion, mild but enough that I would not reach for it on tight architecture or copy work. The out-of-focus rendering is calm rather than characterful. Nobody buys this one for swirl.

The Mamiya 645 is one of the cheapest ways into medium format now, and the plain focal-plane Sekors go for pocket change. The leaf-shutter glass is the exception. Studio and wedding shooters still hunt it down, so it carries a real premium over the standard C lenses, and the obvious cross-shop is the Bronica ETRS, a 645 system built entirely on leaf shutters. The leaf lens is also what lets you keep flash sync at every speed up to 1/500, where a focal-plane body would pin you at its slow X-sync. TTL flash metering, for the record, comes from the body and metering finder on the later Super and Pro bodies, not from the lens, and it works with the standard Sekors too. Anyone not shooting strobe rarely bothers paying up for the leaf glass.

The honest cost is the shutter ceiling. A leaf shutter tops out at 1/500, so if you want f/2.8 in bright sun for shallow depth on that large frame, you cannot get there. You will be screwing an ND onto the front filter thread instead of just spinning to a faster speed. The flash sync earns its keep anyway. When you balance strobe against daylight, meter the ambient in Zone Light Meter first, set that reading on the leaf shutter, then bring the flash up to taste; the lens will sync wherever you leave it.