Mamiya Mamiya-Sekor C 65mm f/4.5

Stop this lens down to f/11 and the corners snap into the same plane of sharpness as the center, which is exactly what you want from a wide on a 6x7 negative and exactly what so many medium-format wides fail to deliver. That across-the-frame evenness is what the 65mm C is built around. Nobody loads it for pretty out-of-focus backgrounds. You reach for it when you need a whole scene rendered cleanly, edge to edge, on a piece of film that is already four times the area of 35mm.

On the RB67 this is the moderate wide, roughly a 32mm equivalent in full-frame terms, and it has to be a retrofocus design to clear the mirror box and the bellows mechanism. Mamiya kept distortion low for that class. Straight lines near the edge stay straight enough that architectural and interior shooters trusted it through the eighties, back when commercial studios ran RB67 bodies as their daily workhorse. Contrast is moderate rather than punchy. Color comes back accurate and a little cool, which played well with the transparency film these cameras were loaded with for catalog and product work.

Wide open at f/4.5 it is soft in the corners and a touch low in contrast, the usual retrofocus penalty, and that is the real weakness worth naming. You rarely shoot it there anyway, because the whole point of a wide on this format is depth of field and resolved detail, so f/8 to f/16 is where it lives and where it is genuinely excellent. One thing this lens does carry that helps it close up is a floating element system, which shifts an internal group as you focus to keep the corners corrected across the focus range. Flare control is decent for the era, but the 77mm front element is large and exposed. Use the dedicated hood, because backlight can wash the contrast flat fast.

The leaf shutter sits in the lens itself, which is the practical reason people still load these bodies for studio work. You get flash sync at every speed up to 1/400, no focal-plane sync ceiling to fight. The tradeoff is the top end stops at 1/400, with no fast 1/1000 escape hatch for bright sun wide open. When you are working with strobes and want a specific aperture for depth of field, set your shutter and aperture as a pair, then let Zone Light Meter give you the ambient reading so you know exactly how much the continuous light is contributing under your flash.

Today these C lenses are cheap, often the cheapest way into serious medium-format wide coverage if you already own an RB67. Worth clearing up the naming: the C in Mamiya-Sekor C marks the multi-coated second-generation line that arrived in 1974 with the Pro S, replacing the older chrome-nose single-coated optics. The later K/L version is the faster f/4 redesign, with improved multi-coating, Mamiya low-dispersion glass, and a refined floating system that adds a bit more bite at wider apertures and a cleaner color and contrast edge. That is the usual cross-shop, often at roughly double the price. For most work the multi-coated C is plenty, especially stopped down, where corner sharpness has never been the complaint. The real cost is the system around it. The RB67 is a heavy, deliberate, tripod-and-cable-release camera, and this 77mm-threaded lens does it no favors on weight. Work it slow and stopped down, the way the format asks, and the negatives hold up to serious enlargement.