mamiya 645 prism finders

I have a mamiya 645 1000s and am looking to upgrade to

a metered prism finder. I have seen several prism finders

advertised ( cds/pds and ae??). Any suggestions as to

the most accurate/problem free prism to purchase.

I've had a Mamiya M645 w/ the CdS prism for about 17 years. As of the publication date (1982) of my M645 manual this and the PD Prism Finder S were the only two metered prisms for the system. Sometime shortly after that they added the AE prism finder. In addition of course there is an unmetered prism and a waste level/sport finder.

 

The CdS prism is coupled only to the lens. The user must insure that the shutter speed on the camera matches the setting on the meter. Varying aperture then gives a TTL reading, changing shutter speeds while viewing through the lens requires changing the camera setting to match. It sounds bad but it never bothered me once I got used to it.

 

The PD Prism Finder S links the shutter speed and aperture together. The lens is linked the same (via a fork/pin arrangement) but the user sets the camera shutter speed dial to the proper setting (it's obvious to the user but my keyboard doesn't have a corresponding symbol). At that point the camera's shutter speed is set by a dial on the prism. The meter is a set of LED's that indicate proper, over and under exposure (I think there are 7 lights), the aperture and shutter speed can then be set while viewing without any changes to the camera body, everything is done on the prism. The fail safe is that the prism receives no power and will not light up unless the dial on the camera is set to the proper position. The CdS prism is independently powered.

 

The AE Prism takes this one step further. Properly set, the prism directly controls shutter speed allowing for aperture priority automatic operation. Although I haven't used one and there is nothing on it in my manual I believe it retains the manual functions of the PD prism in addition. Users with hands on may be able to clarify.

 

I've not had a minutes trouble w/ my prism nor have I heard of any problems with the meters in these prisms. The only complaints I've ever read (no direct experience to date) is with seperation in the cemented elements in the prism. The PD and AE prisms are more sophisticated and likely easier to use but if all you need is match needle metering there is nothing wrong with the CdS. I will warn you that since it is independently powered it is easy to leave turned on and when the battery gets weak the meter still functions but gives bad readings causing a tendency to over expose. Hope this helps.

The meters are usually trouble-free but prism separation and/or corrosion due to rotting foam is _very_ common.

My PD prism now has a visible "line" running horizontally across the field of view, I think this is what John described as a "separation" in the prism. Does anyone know what this "line" is....