How do you tell earlier Mamiya RB prism to later ones? (re: magnifier attachment)

I have, probably the original, prism finder for my Mamiya RB. It's the bulky kind, not the metering kind or the more recent Prism II.

As I understand it, Mamiya makes a magnifier that attaches to the eye port. I am NOT talking about the diopter lens. This is a flip up and down magnifier. I also heard, this magnifier attaches to the later version of this prism and that earlier version require a modification by Mamiya (which it no longer performs).

What I do not know is, how I can tell an earlier version from the later version.

Anyone know??

Here's my understanding:

The original prism is the bulky, primitive looking one - not the sleeker black models.

I have a Pro-S system chart showing the older one as the CdS Prism; the chart shows the newer black prisms (metered and non-metered), but labels them "under development" (and at the time the chart was made, they hadn't been assigned part numbers yet). They don't show the flip-up magnifier in the Pro-S era.

The ProSD system chart shows the two newer finders and has item numbers for 'em - they were in production by the time the SD chart was produced. The flip-up appears on this chart, with a part number.

My RZ chart shows the newer prisms, but doesn't show the flip-up at all (or I'd compare part #'s for you) - but it must have been in production then. I assume it was considered part of the Pro-SD system and they didn't think to add it to the RZ chart. However, my Mamiya book recommends it in the RZ section and the RB section.

Bob Shells' Mamiya book says it is for both systems, RB and RZ.

So - as I understand it - the flip-up is the same part for any RB or RZ "newer pretty sleek style" finder. The RZ has taller mounting screws for finders, so finders aren't interchangeable without installing taller screws - but the flip up should work on any newer prism. It looks to me like both finders are essentially the same as far as their bodies go - the electronics and mounts differ from RB to RZ.

But will the flip-up fit on the old, textured, bulky alien-spacecraft looking finder? I'd assume not, unless the prism has been modified. You may be able to find a good newer prism at KEH or online though. They are pretty nice looking!

I am more familiar with RZ's, so I can't address your question directly.
However, maybe some measurements from the eyepiece of a RZ prism will be helpful.
(Prism's that I know [do indeed] accept the common, flip-up magnifier).

Width: 29mm (inside the groove slots), about 32mm overall.
Height: 18mm. Thickness: about 5.5 to 6mm overall.

If the eyepeice on your RB prism matches these measurements, then you should be good-to-go!

Marc

Marc B.

Thank you. That geometry and measurement is different from mine. Width is 32mm but there is no groove. Height is 28mm overall and 25mm inside the groove. Thickness is 8mm.

I guess I do have the old one that does not take the magnifier.

tkamiya,

I made a mistake in my measurements. The height, or vertical measure is 28mm, not 18.
The grooves run vertical on each side on the outsides of the eyepiece, so my width measurements are accurate.
Sorry about that. I guess I need a magnifier on my ruler.

The magnifier for the RZ slides onto the eyepiece, from the top-down, hence the vertically running grooves..
Your measurements and groove location/orientation seem to indicate that the magnifier for your
prism slides onto the eyepiece horizontally, from side to side(?).

Marc

I have the old one and a magnifier. I can sort of force the magnifier into the slots - it doesn't fit exactly, but it works.
juan