Canon EF-mount lenses

EF launched in 1987 and ran until Canon moved to RF. Canon no longer develops it, which is exactly why it matters: EF is the largest and cheapest used lens market that exists, and every lens on it adapts to RF with full autofocus.

Why buy into a dead mount

Two reasons. If you own a DSLR — a 5D Mark IV, a 6D Mark II, a 90D — EF is simply your mount, and prices have never been better. If you own an RF body, an EF lens plus Canon’s adapter often costs a fraction of the native equivalent for the same optical result.

The L-series telephotos are the clearest case. An EF 70-200mm f/2.8L IS II is optically close to the RF version and sells for a small share of the price.

What to be careful about

Older EF lenses use screw-drive autofocus motors that are slow and loud by modern standards; look for USM or STM in the name. Image stabilization on lenses from before roughly 2010 is a generation behind. And because these lenses are used, condition matters more than specifications — buy from a dealer that grades and warranties, not from a listing with one photograph.

Full-frame and APS-C

EF covers full-frame. EF-S lenses are the APS-C line and do not mount on full-frame bodies at all, so check the format before buying.