Vivitar lens won't work on an EOS R with adapter

[eapples]

Vivitar 8mm 1:3.5 Lens On a Canon EOS R With a Lens Adapter

Hello:  I apologize if I've already posted about this.  I have a Canon EOS R camera.  I use a Canon adapter so that I can continue using the lenses I had on my Canon EOS Rebel.  One of those lenses is a Vivitar 8mm fisheye lens.  It works perfectly on the Rebel, but will not function at all on the EOS R.  When I tried using the lens on the mirrorless camera, nothing worked -- the shutter button would not work; I could not get an aperture reading, nor could I get a reading on any setting on the camera.  I am a technology dinosaur, so my eyes glazed over when I tried to research the issue since I encountered a lot of technojargon.  I am reaching out to the Canon community for some guidance.  Thank you in advance for your help.

[shadowsports]

@eapples ,

Let's take this further.  

Try enabling crop mode on the camera's shooting menu.  This might help to minimize or eliminate the vignetting you are seeing using the EF-S lens on a full frame camera.  Also worth noting, using this lens on your camera will reduce its 30 megapixel image capture capability to approx 11 megapixels.  Just be aware of this.