Beware the gmp111-0.It looks like the previous mini - gmp111 but has a different constant. Last I saw Leica still hadn't put it in the menu and you needed to choose round prism to get the right constant.
We had one that looked like that. I think it was made by Omni. I don't think it was reversible, I.e. 0/30. You should go through the empirical procedures that have been described. Good luck.
See this link. Sure looks like yours.
Omni Prism
If your (AC)-(AB+AC) does not yield a result of -30 mm I will be shocked.
That is not to say there were no similar prisms manufactured that didn't have a 30 mm offset value but that has not been typical in the nearly 16 years I've been selling equipment.
Some cautions:
I bought a triple-prism setup of that style on ebay for a long distance measurement, and found that the glue had given way so all the prisms slid back and forth in the housings. Whether in shipping or previous to sale I don't know. One had chipped the point of the glass by hitting the back of the housing so there is a little star in the center of the image.
There seemed to be no way to open the housing, so I got them slid to where I thought they should be and glued them around the front edge. I think I got them within a mm, but need to re-measure them if I use them for anything critical.
If the seal isn't good you can get condensation on the back of the glass and it will leave residue that reduces the clarity of the image and thus the range. I was cleaning the front with glass cleaner and foolishly got liquid inside. Sigh.
I do believe that is a -30mm prism. There were several manufactures over the years. If it has and alum canister is is older and a good working unit. If if has a plastic barrel then is is newer. The backside of the canister un-screws, and you will find a chunk of foam in there to hold the prism up against the inner lip of the canister. The plastic ones do not have a rubber gasket between the lip and the prism, the alum ones do.
Good prisms, you can beat the hell out of them and they will keep on ticking.
> I do believe that is a -30mm prism. There were several manufactures over the years. If it has and alum canister is is older and a good working unit. If if has a plastic barrel then is is newer. The backside of the canister un-screws, and you will find a chunk of foam in there to hold the prism up against the inner lip of the canister. The plastic ones do not have a rubber gasket between the lip and the prism, the alum ones do.
>
> Good prisms, you can beat the hell out of them and they will keep on ticking.
It's aluminum. When I got it, the prism was rattling around, so I unscrewed the back (it was on TIGHT!), and thought..."that needs a piece of foam in there to keep the prism up against the inner lip of the canister".... I put one in and took it for a spin. The coating on the back surface of the prism is worn off near the outer edges; I don't think it affects the reflectivity at all. If my 10th grade Physics memory is correct, the beam reflects via internal refraction, not silvering as in a mirror, but I could be wrong there.
All I know is that for $10, it works pretty well.
Correct, and you have an older one for sure. We had one with the silver chipping off, and one without any silver at all. When I cleaned the oldest one I cleaned all of the silver off, and it did not effect the performance one bit. Great find for $10!
