This sale is for a Mamiya RB67 / RZ67 Eye Correction Lens -1.5 Dioptre for the standard RB and RZ type waist level finders (WLF). Mamiya did not always mark the standard dioptre with a value, but this definitely is a -1.5D.
This dioptre simply clips into the waist level viewfinder. This dioptre is very clean with minimal signs of use, just not quite as new. This is the standard dioptre supplied with all new RB67 (ProS and ProSD) and RZ67 WLF, and is there for image magnification – it has nothing to do with eyesight correction as such. Ideal if you have a WLF with a non-standard dioptre that you want to restore to its normal condition. Please note that this dioptre will not fit the original RB67 Pro WLF (the one without the locking mechanism on the sliding mounting bar).
Now very hard to find.