Canon's Serenar rangefinder tele — 100mm f/4 in Leica Thread Mount, manual focus.
The Canon Serenar 100mm f/4 is a telephoto rangefinder lens made in Japan for the 39mm Leica screw thread. It dates from the late-1940s Serenar period of Canon's rangefinder line, among the company's early longer optics. It gave Leica-thread and Canon rangefinder users a compact 100mm reach for portraits and distant subjects.
This is a manual-focus, rangefinder-coupled Leica Thread Mount lens with a 100mm focal length and a maximum aperture of f/4. The mount is the 39mm Leica screw thread (LTM / L39 / M39). Focus and aperture are set on the barrel by hand. Element count, weight and filter thread are omitted here because they are not verified from the gap data.
A 100mm gives useful reach beyond the standard portrait length, good for tighter portraits, distant detail and compressed perspective. At f/4 the lens stays compact and is best used in good light, and slower teles of this design tend to be sharp across the frame when stopped down slightly. It suits travel and general longer-lens work.
Buying used, inspect these early Serenar teles for haze, fungus and balsam separation in the cemented groups. Check the coatings for cleaning marks and wear, look for oily aperture blades, and confirm the focus helicoid is smooth. Rangefinder-coupling accuracy matters at 100mm, so test it on a body. It adapts well to Leica M via M39-to-M and to mirrorless with M39-to-E, M39-to-Z or M39-to-RF adapters.