Anatomy of a cheap roof prism

[Tero]

This one was an 8x21 roof prism, before I sawed it open. Looks to be aluminum partly:
http://i9.photobucket.com/albums/a57/Tero1111/bino1.jpg
The small lenses next to it, and the metal ring, were the eye piece. There was a plastic barrel inside the metal one that moves the 21mm lens back and forth. Normally the big lens does not move.

Inside the barrel was a housing holding the two prisms. The first one that came out is shown here, along with metal pieces tha held it in place.
http://i9.photobucket.com/albums/a57/Tero1111/bino3.jpg

With some jiggling, the other prism came out. The left one is toward the eye piece.
http://i9.photobucket.com/albums/a57/Tero1111/bino2.jpg
It sure was strange looking, and I did not figure out how they had fit together, but one rested on the other somehow. I guessed that the point had to face the eye piece, then you have two flat glass surfaces against each other. The right one has a mirrored surface inside, painted black outside.

OK, I have not learned much. But the prisms fit in nicely, smaller than I expected. I guess they are at the point where the beam of light is fairly narrow.

[Tero]

OK, I get it now, I have them in my hand and they do fit together like this
http://en.wikipedia.org/wiki/Schmidt-Pechan_prism

I have some pretty good Minolta 8x25s, the 25mm lens also moves back and forth inside the barrel to focus. May be typical of small roof pirsms.

[Tero]

I took some more pictures. This is how they were inside the binocular, and the two prisms on their own.The wedge one has a mirrored surface, just like any mirror.

You can hold the prisms up and view and see a 1x view of the scene.

[Kevin Purcell]

Useful photos. I could have used those when trying to figure which surface was mirrored!

Are the spots on the side where they were glued in place?

Focusing roofs seem to have many focusing mechanisms: move the objectives, move a negative lens element in front of the prisms, move a lens element (postive) behind the prisms, move the eyepieces (I think I have a Nikon patent from the early 1990s showing that).

[Kevin Purcell]

Useful photos. I could have used those when trying to figure which surface was mirrored!

Are the spots on the side where they were glued in place?

How big are those prisms? I don't have a CF card handy to compare.

Focusing roofs seem to have many focusing mechanisms: move the objectives, move a negative lens element in front of the prisms, move a lens element (postive) behind the prisms, move the eyepieces (I think I have a Nikon patent from the early 1990s showing that).

[Tero]

Would you like to have these? I can send them to you. ;) I may have the lenses too. With popsicle sticks, silly putty and some rubber bands you could build a binocular. I may not have the objective lenses, thery were pretty stuck in there.

The long length on the wedge is 23mm and the "roof" prism 15-17mm, depending on which direction. This was for a 20mm binocular, as I said.

One is chipped a bit, they are not much use. There were thin metal things holding them in place and there are two unground sides to each with dabs of glue.

[Kevin Purcell]

Thanks Tero. Just getting a feel for the sizes of these bits. About the same order of size as the objective (not too suprising!).

And I think I'll pass on your offer. I have enough bins with stray light problems that aren't built from popsicle sticks ;)