Mamiya's 645 tele zoom — the manual-focus Sekor C 105-210mm f/4.5, constant aperture.
The Mamiya Sekor C 105-210mm f/4.5 Zoom is a telephoto zoom lens for the Mamiya 645 medium-format system. It covers a short-tele to medium-tele range, complementing the standard 55-110mm zoom at the longer end of the line. Zooms were unusual on medium format, and this one gave portrait-to-telephoto flexibility in a single optic.
This is a manual-focus lens native to the Mamiya 645 bayonet mount, with a zoom range of 105-210mm and a constant maximum aperture of f/4.5. The zoom and aperture are set mechanically on the barrel. The optical design covers the full 645 image circle across the range, delivering consistent telephoto framing from portrait length to longer reach.
The 105-210mm range on 645 corresponds to roughly a 65mm to 130mm equivalent on 35mm, a practical portrait-to-telephoto span. The constant f/4.5 aperture holds exposure steady through the zoom, and the compression at the long end suits portraits and distant detail. It trades a little of the sharpness of a prime for the convenience of covering several focal lengths at once.
This telephoto zoom is less common than the prime telephotos and appeals to those wanting reach without swapping lenses. Inspect the element groups for haze, fungus and separation, confirm the aperture blades are oil-free and close cleanly, and test the zoom and focus actions for smooth travel without play. Check the front coating for scratches and verify the mount and coupling before buying.