# Canon RF mount: 20 mm flange focal distance, 54 mm diameter

> What is the Canon RF flange focal distance and throat diameter?

- Category: Cameras & lenses › Lens mounts & filter threads
- Kind: Standard part
- Basis: Published numbers only (sources per row); no bayonet geometry is published, so no file
- Page: https://xemstudio.com/objects/canon-rf-mount/ · JSON: https://xemstudio.com/api/geometry?object=canon-rf-mount · Plain text: https://xemstudio.com/objects/canon-rf-mount/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
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**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Flange focal distance is the distance from the mount's reference face to the image plane; adapters and extension tubes must add exactly the difference between two mounts' flange distances to keep infinity focus.
- RF replaced EF on Canon's mirrorless bodies: the 54 mm diameter stayed, and the flange distance went from 44 mm to 20 mm, which is why an EF-to-RF adapter is 24 mm thick.
- No file: the bayonet's lug widths, angles, depths and locking geometry are not published by the maker, so nothing is drawn. Only the published numbers are given.

## Sizes

| parameter | value | from |
|---|---|---|
| flange focal distance | 20 mm | Canon (lens mount guide) |
| throat / inner diameter | 54 mm (mount diameter) | Canon U.S.A. press release, 2018 |
| coupling | bayonet | — |

## Where the files are

- Canon: [Camera lens mount guide (RF: 20 mm flange distance)](https://en.canon-me.com/get-inspired/tips-and-techniques/choosing-right-lens-mount/) — web — Publisher's page; dimensions are facts
- Canon U.S.A.: [Canon introduces four RF mount lenses (press release, 5 Sep 2018): RF mount 54 mm diameter](https://www.usa.canon.com/newsroom/2018/20180905-rf) — web — Publisher's page; dimensions are facts
- Wikipedia: [Flange focal distance (table of mounts)](https://en.wikipedia.org/wiki/Flange_focal_distance) — web — CC BY-SA 4.0 (text); dimensions are facts

## Questions

**What is the Canon RF flange distance?**

20 mm, with a 54 mm mount diameter (Canon).

**Why is the EF-to-RF adapter 24 mm thick?**

EF has a 44.00 mm flange distance and RF 20 mm: 44 − 20 = 24 mm.

## Fits with

- [Canon EF mount: 44 mm flange focal distance](https://xemstudio.com/objects/canon-ef-mount/)
- [Sony E-mount: 18 mm flange focal distance](https://xemstudio.com/objects/sony-e-mount/)
- [Nikon Z mount: 16 mm flange focal distance, 55 mm inner diameter](https://xemstudio.com/objects/nikon-z-mount/)
- [Lens filter threads: M40.5 × 0.5 to M112, pitch table and thread rings](https://xemstudio.com/objects/lens-filter-threads/)