RF lens to L mount

[iRoxUrSox]

So my current main camera is a Lumix S1R for landscape and 360° photography, and for which I use some Canon EF lenses using an EF-to L mount adapter. I want to use the RF 5.2mm F2.8 L Dual Fisheye lens on my S1R to avoid having to buy an entire Canon R camera just for one lens. I know there's no RF to L-mount adapter, and I know there's no RF to EF camera adapter. So I'm wondering - what may be the facts that prevent me from putting an RF lens on my EF to L-mount adapter - the difference in back focus? Any way I can compensate for that?

[rs-eos]

Physics.  Specifically the flange distance.  Or, put more simply, for the same reasons that there cannot exist an RF to EF adapter (i.e. no way to mount an RF lens onto an EF mount camera), there's no way to mount an RF lens onto an EF-to-something adapter of any kind.

[AtticusLake]

Ricky has it.  The RF lens needs to be exactly 20mm from the camera's sensor; but the front of the L mount is exactly 20mm from that camera's sensor.  This leaves exactly 0mm for an adapter, which is impossible.

As for EF -- an EF mount holds the lens 44mm from the sensor, so there's no way you could use any mirrorless lens on there.  So you can adapt an EF lens to an RF camera, but not the other way around.

I wrote an article which explains all this, if you're interested: https://moonblink.info/MudLake/gear/lenses