This sale is for one excellent condition Mamiya 645 Eye Correction Lens -3.0 D for the Super/Pro/ProTL Prism / AE Prism, Mamiya 6MF, and Mamiya 7/7ii. I have other dioptres available, and if you cannot see what you want just ask.
This dioptre simply slots in to the back of the viewfinder on your prism, or Mamiya 6MF or 7 camera. This dioptre is has minor signs of use on the plastic frame edge (no effect on use) but the glass is perfect.
A large (but definitely nowhere near complete) selection of Mamiya, Bronica and Fuji GX680 dioptres available and I do not have time to list them all; if you cannot see the one you want then just ask.
Note that this dioptre is not suitable for the earlier M645 prisms for the M645, M645J and M645 1000S. Waist level finders and other prisms need different dioptres.