AE Prism finder "N" for the Mamiya Super 645

[waynecrider]

Does it meter pretty good? I was thinking about going with a newer Pro AE prism, but I just read over in the Mamiya forum that the Pro AE 401 prism will not meter on the Super body. I'm wondering if that extends to the Kepler style prism FK402 as well.

 

[MattKing]

I am very happy with my AE "N" prism and its meter on my Super bodies, and it works well on my "Pro" body as well. It takes some getting used to, with its three choices (averaging, or spot, or automatically choosing between the two) but once you familiarize yourself, it is great.

I am not sure why there is incompatibility between the finders and the newer bodies, unless it has something to do with the TTL function in the Pro TTL.

 

[Paul Sorensen]

I have also heard that there are metering issues between the bodies. I have the N and I think it meters well. I don't know what kind spot angle it provides, I am sure it's pretty big. I also have no clue about the auto select and how it chooses. I just leave it in average unless I have a specific reason to use the spot setting.

 

[waynecrider]

Thanks. The only reason I asked is that I ran across a negative thread on the "N" meter. For clarification, the "N" will work on the newer bodies, the newer prisms will not meter on the older bodies, but can be used as prisms and will fit. I waiting on word from Mamiya as to upgrading an older body to use the newer prisms, but then, why? The "N" prism is cheaper, but I just want to know if it can be done.

 

[MattKing]

I have also heard that there are metering issues between the bodies. I have the N and I think it meters well. I don't know what kind spot angle it provides, I am sure it's pretty big. I also have no clue about the auto select and how it chooses. I just leave it in average unless I have a specific reason to use the spot setting.

Here is an some information about the the spot angle from the Mamiya Forum:

"The spot measurement angle varies with the lens in use. For example, the 500mm lens has a 1 degree angle, the 150mm is 5 degrees, the 80mm is 8 degrees and the 45mm is 15 degrees. "

I am not sure whether this works linearly, but in the case of the 80mm lens, which has an angle of view of 47 degrees, the spot angle is approximately 1/6 of the angle of view of the lens. In comparison the 150 mm lens has a 26 degree angle of view, so the spot angle is about 1/5 of that, and the 45mm lens has an angle of view of about 76 degrees, so again the spot angle is about 1/5 of that.

I expect that these angle of view measurements are based on a horizontal format. I don't know what the shape of the area of sensitivity is (round, eliptical but horizontal, eliptical but vertical, or ??)

Thinking about all this, I think it might be useful to get some clear plastic, cut it to the size of the viewing screen, and pencil in markings near the centre showing the area that represents about 1/5 the angle of view. Then compare that to the markings on the viewing screen. Finally, find a point source of light, and carefully move the camera, so as to observe where on the field of view the spot meter reacts to the light, and where it doesn't. That would likely give some information about the shape of the area of sensitivity.

A grid screen would probably help too. It also may not be possible to insert the clear plastic between the viewing screen and the prism.

Does anybody else have any thoughts about this?