RB67 old style metered prism, any experience?

[xtolsniffer]

Dear all,
I recently acquired an old-style metered prism for an RB67 (not the newer style that also fits the RZ), does anyone have any experience with this prism finder? I can figure most of it out myself, but what's the little red button for to the right of the viewfinder? Also, what type of batteries does it take? I've put alkaline LR44's in, but it seems to underexpose by about a stop compared with two of my Nikon bodies. I guess it's not that suprising given the age of the thing, but is this to be expected? I've taken it apart for a good clean (surprisingly easy, there's not that much in them), and it's a good deal smoother after, but the stop difference is still there - I'm using a standard Mamiya screen by the way.

 

[xtolsniffer]

oops, I think I mean it overexposes - to get the correct exposure reading for ISO 100 film I have to set it to ISO 200.

 

[maclin]

Xtol, the red button is supposed to test the level of the batteries. The prism/meter uses two (2) 357 (Energizer #). Make certain that the surface of the mirror is clean. A light coating of dust or anything will obviously affect the meter reading.

 

[xtolsniffer]

Hmmm, I thought as much, is it supposed to light up an LED or something as mine doesn't!

 

[Photo Engineer]

Make sure that the ring around the speed setting control is pointing to zero and not to an offset such as -1. That will give a 1 stop underexposure.

PE

 

[Alexander Ghaffari]

Yep, I have one. It works fine (just heavy and no fun of shooting with a WLF). I use silver oxides so that metering is more consistent as the batteries discharge over time (the instruction manual says to use silver oxides of the type you have used, so alkalines work fine as long as they have not been used for awhile). Batteries will not discharge when the prism is off the body, but they will discharge if it is turned on and left on the body (be aware, that has happened to me by accident and fresh batteries died, but I did not need it at the time, luckily). Make sure that you set the ring next to the ASA/ISO dial to the widest aperture on that particular lens mounted to the body because it will certainly be off if you have a f/3.8 lens attached but it is set to f/6.3.

The lit LED when pushing the button is supposed to denote adequate battery charge. If it does not work and fresh batteries are installed, then a damaged resistor is likely the culprit...no biggie if the meter actually works...just keep fresh batteries on hand.

 

[xtolsniffer]

Cheers people - it seems the battery indicator does work, but only when used with silver oxide batteries, even new alkaline LR44's will only make it work now and then. Given that there is no voltage regulation circuit in there, I guess silver oxides are a must to make sure that exposure doesn't drift with time. Still overexposes by a stop though....