Canon's bellows macro lens — the FL 100mm f/4 designed for macro with bellows system.
The Canon FL 100mm f/4 FLM is a dedicated bellows macro lens from Canon's FL mount era, designed specifically for use on a bellows unit rather than directly on a camera body. The FLM (FL Macro) designation indicates it lacks a conventional focus helicoid — focus distance is controlled entirely via the bellows extension.
The lens delivers 100mm at f/4 maximum aperture in a barrel designed for bellows mounting, with Canon FL mount coupling, fully manual aperture via the aperture ring, and optimised flat-field optics for close-up reproduction work. Without a bellows unit, it cannot focus to infinity and is not usable as a standard prime lens.
Bellows macro lenses offer exceptional image quality for 1:1 and higher magnification work because their optical formula is optimised for close-distance reproduction rather than infinity focus — the opposite priority from standard lenses. The 100mm focal length provides working distance from the subject. These are specialist darkroom and scientific photography tools.
Verify the lens seats correctly in the Canon FL bellows mount. Test aperture blade operation across all stops. Inspect element surfaces for haze, fungal growth, or coating damage — bellows lenses are frequently stored without protection. Confirm flat-field correction quality by testing on a copy stand with a fine-detail document. A compatible Canon FLM bellows unit is required for use.