Why the mount matters, not just the brand
A lens only physically attaches to the one mount it was built for. Buying a lens that matches your camera's brand is not enough on its own, because most brands sell lenses in more than one mount family - usually one for their DSLR bodies and a different one for their mirrorless bodies. Fit the wrong mount with no adapter and the lens will not attach at all.
Canon: more than one mount family
Canon's DSLR line uses the EF and EF-S lens mounts - EF lenses fit any EF-mount DSLR, while EF-S lenses are built only for Canon's APS-C (crop-sensor) DSLR bodies and do not fit full-frame EF bodies. Canon's current mirrorless cameras (the EOS R series) use a separate RF mount; an EF or EF-S lens only fits an RF-mount body with Canon's official EF-EOS R adapter, sold separately. Canon also sold an older, now-discontinued mirrorless system (EOS M) on its own EF-M mount, which is not interchangeable with EF, EF-S or RF without a Canon-made adapter either.
Nikon: F-mount (DSLR) and Z-mount (mirrorless)
Nikon's DSLR bodies use the F-mount, a design Nikon has kept in production for decades. Nikon's mirrorless Z-series bodies use a separate Z-mount. An F-mount lens only fits a Z-mount body with Nikon's FTZ or FTZ II adapter - it does not attach directly.
Sony: one current mount, E-mount
Every current Sony mirrorless camera, APS-C and full-frame, uses the same E-mount, so a Sony E-mount lens fits any current Sony mirrorless body without an adapter. Sony's older A-mount SLT/DSLR-style cameras are a separate, now-discontinued system and need Sony's LA-EA adapter to use an E-mount lens, or the other way round.
Fujifilm: X-mount
Fujifilm's interchangeable-lens cameras share a single current lens mount, X-mount, so any Fujifilm X-series lens fits any Fujifilm X-series camera body directly, with no adapter needed.
Third-party lenses: same brand name, different mount versions
Sigma, Tamron, Viltrox, Tokina, Samyang and Yongnuo lenses are each made for one specific camera mount, and the same lens model is usually sold in separate Canon, Nikon, Sony and Fujifilm versions by the manufacturer - the brand printed on the lens tells you who made it, not which mount it fits.
Confirm the exact mount before you pay
Our lens listing titles name the focal length but not always the exact mount, because some of these focal lengths exist in more than one mount version from the same manufacturer. Ask us on WhatsApp for the exact mount, with photos of the lens mount markings on the actual unit, before you pay. See our guide on how we list a used camera for how we handle this kind of confirmation generally.