Canon EF to Canon RF adapter thickness
A glassless Canon EF to Canon RF adapter must be about 24 mm thick to keep a Canon EF lens focusing correctly on a Canon RF body. This equals the Canon EF flange focal distance minus the Canon RF flange focal distance, both published mount-design constants, reviewed 2026-09-12.
How this is computed
Using the Canon EF flange-to-sensor distance as a one-component train against a backfocus target equal to the Canon RF flange focal distance (filter correction off), BackfocusLab's own model reports the spacing gap between them as the required adapter thickness.
- Source mount (lens side)
- Canon EF, 44 mm FFD
- Target mount (body side)
- Canon RF, 20 mm FFD
- Adapter thickness
- 24 mm
This is illustrative arithmetic, not a substitute for the manufacturer's own adapter specification; small machining tolerances exist. A dumb, glassless adapter only forwards the mechanical mount; it makes no claim about autofocus, aperture control, or electronic contacts, and a nominal fit is not a compatibility guarantee. Verify against your camera manufacturer's published specification before ordering.
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