Please re-read my post. I have a 5D sr and an RP, both ff bodies, they both allow ef-s and third party lens to mount. If the lens is a Canon ef-s, they both switch to crop mode automatically. If the lens is third party, the switch must be accomplished manually through the menu.
Yes, your EOS RP mirrorless can accommodate EF-S lenses... but an adapter is required and when the 26MP image is cropped to APS-C format, you'll have roughly the equivalent of a 10MP 40D from 2007.
No, your 5DsR DSLR cannot be fitted with an unmodified EF-S lens. The camera and the lenses are specifically designed to prevent that.
EF-S lenses will mount on full frame bodies but several Canon bodies have mirrors that hit the extension on an EF-S lens. Not good for the mirror!!
No, unless modified, by design EF-S lenses WILL NOT mount on ANY Canon full frame body.
You are correct, though, that using a crop-design lens on a full frame Canon DSLR is risky. but, it's not "several Canon bodies" that have mirrors. ALL full frame Canon DSLRs have mirrors that SOME EF-S lenses might interfere with. It depends upon the lens.... All the DSLRs use the same dimensions (44mm lens register) and have mirrors sized to accommodate the full frame format. You are correct that it's would not be a good thing for the mirror, should there be interference. Figure on spending a serious chunk of money getting it fixed.
Third party manufacturers don't make EF-S lenses. They make "full frame" and "crop-only" lenses, and both types designed for use on Canon use the same EF mount. As a result, either type of third party lens will mount to a full frame DSLR... but you do so at your own risk. You might damage the camera if the lens' rear element protruded inside the camera body, the way some crop design lenses do.
[quote=DeanS]“EF lenses are not to be used on EF-S camera bodies.”
Totally incorrect. ALL Canon EF lens work very well on Canon crop bodies....[quote]
You are right about that. First, there's no such thing as an "EF-S camera body". There are "APS-C" Canon DSLRs and mirrorless camera. Second, ALL EF lenses will work on all Canon APS-C bodies.
In fact, every APS-C camera since the Digital Rebel (aka, 300D) was introduced in 2004 has been fully compatible with BOTH EF lenses and EF-S lenses. (The earliest APS-C models - D30, D60 and 10D - produced from 2000 to 2004 - preceded the introduction of EF-S lenses and cannot be fitted with them.)
It's the full frame Canon DSLRs (and the discontinued APS-H bodies) that are limited to what they can use.... EF only (which still gives you choice of 60 or more Canon lenses currently in production).
....What is a fact, Canon EF-S lens WILL NOT mount to some Canon FF bodies.
Again, the FACT is that unmodified EF-S lenses will not mount to ANY full frame Canon DSLR (or any of the 1D-series APS-H models).