Canon's FD-mount 135mm telephoto — breech-lock version with good optics for film portrait work.
The Canon FD 135mm f/2.5 B/Lock is a manual-focus telephoto prime for Canon FD-mount, released approximately 1975 in the breechlock (B/Lock) variant. Six elements in 5 groups. Eight aperture blades. 58mm filter thread. At approximately 350g. ~1.5m MFD. Breechlock attachment mechanism.
Six elements in 5 groups. Eight aperture blades. The 58mm filter thread. At approximately 350g. Minimum focus distance approximately 1.5m. Manual focus only. Breechlock (B/Lock) attachment. f/2.5 maximum aperture. Full-frame coverage. Canon FD mount.
The 'B/Lock' designation indicates the breechlock attachment mechanism: the lens screws onto the body using a rotating metal ring around the rear mount, rather than a simple bayonet twist. The breechlock design was Canon FD's original mounting system before the new-FD bayonet was introduced in 1979. The 135mm f/2.5 provides a moderate telephoto with fast aperture for the era.
On the used market the Canon FD 135mm f/2.5 B/Lock is affordable as a vintage manual-focus telephoto. Condition checks: focus helicoid smoothness, aperture blades for oil, 58mm front element for marks, breechlock mechanism. Manual focus only. Canon FD mount — not compatible with EF/RF without optical adapter.