Canon's original EF 50mm f/1.8 — the first version of the legendary 'nifty fifty' for EOS.
The Canon EF 50mm f/1.8 is Canon's standard fast prime for EF-mount full-frame, available in two versions: the original Mark II (6 elements/5 groups, 5-blade, 52mm filter, 130g, 0.45m MFD) and the current STM (6 elements/5 groups, 7-blade, 49mm filter, 160g, 0.35m MFD). Both provide f/1.8 maximum aperture.
Mark II: 6 elements in 5 groups, 5 aperture blades, 52mm filter thread, 130g, 0.45m MFD, screwdrive AF. STM: 6 elements in 5 groups, 7 aperture blades, 49mm filter thread, 160g, 0.35m MFD, STM motor. Both: f/1.8 maximum aperture, full-frame coverage, Canon EF mount.
The EF 50mm f/1.8 (both versions) is among the most affordable fast primes for any camera system: the f/1.8 aperture on full-frame provides shallow depth-of-field for portraits and good low-light performance at very low cost. The STM version added a stepper motor for smoother video AF, improved 49mm filter thread, and 7-blade aperture versus the Mark II's 5-blade design.
On the used market the Canon EF 50mm f/1.8 is very affordable as a fast normal prime. Condition checks: AF response, front element for marks. Confirm which version (Mark II: 52mm filter, 5 blades; STM: 49mm filter, 7 blades). Compatible with Canon EOS EF bodies; on RF via EF-RF adapter.