Review (5/5): built in ARCA mount
I bought this mount ring for a Canon EF 70-300mm f/4-5.6L. The fit and finish is very nice. It does not scratch the white paint on the lens. It has a built in ARCA compatible mount which was a requirement for me. It is machined with rounded corners so it feels nice when hand holding the lens. The screw knob is spring loaded and must be pulled out to release the connection to the other half of the collar. It is easy to install and remove and holds the lens tight. My only complaint is that the screw knob is in an awkward location when hand holding the lens.