Mamiya's 645 standard zoom — the manual-focus Sekor C 55-110mm f/4.5 N, constant aperture.
The Mamiya Sekor C 55-110mm f/4.5 N Zoom is a standard-range zoom lens for the Mamiya 645 medium-format system, introduced in 1984. The N designation marks it as part of the revised N-series generation that updated the earlier C-series optics. Zoom lenses were uncommon on medium format, and this one spanned a useful wide-to-short-tele range.
This is a manual-focus lens native to the Mamiya 645 bayonet mount, with a zoom range of 55-110mm and a constant maximum aperture of f/4.5. The aperture and zoom are controlled mechanically on the barrel. The design covers the full 645 image circle throughout the range, delivering wide-normal to portrait-length coverage in a single lens.
The 55-110mm range on 645 spans roughly a 34mm to 68mm equivalent on 35mm, covering wide-normal through short telephoto. The constant f/4.5 aperture keeps exposure consistent as the focal length changes, which is convenient for varied shooting. It suits travel and general work where carrying several primes is impractical, trading a little outright sharpness for flexibility.
This N-series zoom is less common than the primes and appeals to photographers wanting one-lens convenience on 645. Check the multiple element groups for haze, fungus and separation, confirm the aperture blades are dry and close cleanly, and test both the zoom and focus mechanisms for smooth, even movement without wobble. Inspect the front coating for scratches and verify the bayonet and coupling are tight.