This adapter has a built-in de-clicked iris which allows for some degree of control over the light coming in from the lens. Some M645 lenses use an electronic aperture which will not function with an adapter, the built-in iris enables the lens to still be used with some functionality. The Fotodiox Pro line of adapters is crafted in Fotodiox’s factory with excellence in mind. Our adapters are manufactured with precise tolerances, providing a solid, gap free, no wiggle connection for stress free use. No adjustments needed! Fotodiox adapters are meant to be taken off and put back on your camera as much as needed while remaining as precise as the day you bought them. Fotodiox Pro adapters feature all-metal, no plastic construction to create a secure connection between your glass and camera that will not degrade over time, keeping the lens-camera connection secure with every use. We use chrome plated brass mounts for enhanced durability and reliability. Compatible Canon RF-mount Cameras (including but not limited to): EOS R, EOS RP Please Note: Phase One M645 lenses will not fit this adapter, only older Mamiya M645 lenses will fit properly. As you stop down the adapter iris, you may experience vignetting at a certain point. This is a manual adapter, so lens functions that rely on electronic communication with the camera body (autofocus, AE metering, image stabilization, etc.) will be disrupted. We state “infinity focus allowed” because our adapters are designed to be universal which can prevent some lenses from focusing to infinity at the infinity mark. Set your camera to “Manual’ or ‘Aperture Priority’ for metering. If camera does not release be sure to enable ‘shoot without lens’ in camera settings. All pictures are for illustration purposes only. Actual product may vary slightly due to ongoing improvements in design.