topic Re: EOS R8 Back focus distance in EOS DSLR & Mirrorless Cameras

EOS R8 Back focus distance

Tony1965 — Tue, 20 Jun 2023 12:51:04 GMT

Does anyone know the back focus on the R8?

Re: Back focus

shadowsports — Mon, 19 Jun 2023 18:04:08 GMT

Hi Tony,

Can you clarify? What are you trying toto do exactly. Sounds like BBF but not sure.

Re: Back focus

deebatman316 — Mon, 19 Jun 2023 18:31:31 GMT

What do you mean by back focus.

The lens is back focusing. This is NOT possible on a Mirrorless camera. But it can happen on an SLR/ DSLR camera.
Or do you want to setup BBF. This decouples the shutter and AF Start Button. The AF Start Button can be moved to the "AF-ON" or "★" button.

Re: Back focus

Tony1965 — Mon, 19 Jun 2023 19:48:15 GMT

From the face of the sensor to the flange for the lens.

Re: Back focus

deebatman316 — Mon, 19 Jun 2023 20:15:55 GMT

The RF Mount uses a 20mm flange distance. The diameter of the mount is 54mm which is the same as the EF/ EF-S Mount

Sensor

Tony1965 — Mon, 19 Jun 2023 22:18:30 GMT

Does anyone know the distance from the sensor to the lens flange?

Re: Sensor

Anonymous — Mon, 19 Jun 2023 22:25:47 GMT

The sensor focal plane is marked on the camera body. You can measure from that mark to the lens flange. Focal Plane symbol is shown below:

Re: Sensor

shadowsports — Mon, 19 Jun 2023 22:36:02 GMT

Hi Tony1965,

Are you shopping for a new camera? You have another post with a similar question:

Back focus - Canon Community

Re: Sensor

MikeSowsun — Tue, 20 Jun 2023 14:43:12 GMT

It looks like 2 questions have been merged.

The distance from the sensor to the lens mount is called “Flange Focal Distance” but it can also be called “Back Focus”.

The distance is 44mm on Canon EOS SLR and DSLR cameras like the 80D.
The distance is 20mm on Canon EOS R series Mirrorless cameras like the R8.

You can find the distance for almost any camera on the Wikipedia page called Flange FocalDistance

“For an interchangeable lens camera, the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), back focus or register, depending on the usage and source) of a lens mount system is the distance from the mounting flange (the interlocking metal rings on the camera and the rear of the lens) to the film or image sensor plane. This value is different for different camera systems. The range of this distance, which will render an image clearly in focus within all focal lengths, is usually measured to a precision of hundredths of millimetres, and is not to be confused with depth of field.”

Re: Back focus

MikeSowsun — Tue, 20 Jun 2023 00:19:53 GMT

“Back Focus” is sometimes used instead of Flange Focal Distance.

Re: Sensor

jrhoffman75 — Tue, 20 Jun 2023 11:10:41 GMT

Hi Tony. Just curious as to why you want to know this? (Always looking to learn.)

Re: EOS R8 Back focus distance

Ian_D_Head — Tue, 20 Jun 2023 13:18:44 GMT

New around here, hope you accept an answer from the UK 🙂

It's 20mm

Re: Sensor

Tony1965 — Tue, 20 Jun 2023 13:23:00 GMT

So I can attach it to my telescope for Astrophotography.

Re: EOS R8 Back focus distance

Tony1965 — Tue, 20 Jun 2023 13:23:48 GMT

Yea

Re: EOS R8 Back focus distance

Ian_D_Head — Tue, 20 Jun 2023 13:29:26 GMT

Realised it has now been answered earlier. But it gave me an excuse for my first post.👍