CANON EF 20mm f/2.8 USM

JP H08-110467 A — Tadashi Endo

11 elements / 9 groups
Patent EFL 20.498624 mm; retained at printed scale
f/2.8 marketed; f/2.9 patent design
94° marketed diagonal field; 93.1° patent field
All-spherical negative-positive retrofocus
Rear focus; complete L2 moves objectward

Focus Mechanism

Rear focus: fixed negative L1; complete positive L2, including the stop, moves 2.977699 mm objectward in the paraxial 0.25 m reconstruction.

Optical Elements (11 physical)

ElementTypeGlass
L11Negative MeniscusS-BSM15 (OHARA 623582 coordinate equivalent)
L12Negative MeniscusS-BSM14 (OHARA 603607 coordinate equivalent)
L13Biconvex PositiveS-BAL42 (OHARA 583594 coordinate equivalent)
L21Negative MeniscusS-LAH66 (OHARA 773496 historical/current special-order coordinate match)
L22Positive MeniscusPBH6 / S-TIH6 coordinate (OHARA 805254 equivalent; actual melt unspecified)
L23Biconvex PositiveS-BSL7 (OHARA 516641 coordinate equivalent; catalog νd = 64.14)
L24Biconcave NegativeTIM11 (OHARA historical 621359 exact coordinate match)
L25Positive MeniscusPBH6 / S-TIH6 coordinate (OHARA 805254 equivalent; actual melt unspecified)
L26Biconcave NegativePBH53 (OHARA historical 847239 exact coordinate match)
L27Biconvex PositiveS-FSL5 (OHARA 487702 coordinate match)
L28Biconvex PositiveS-LAH66 (OHARA 773496 historical/current special-order coordinate match)