Are prisms interchangable

[allcart]

I now have 3 pairs of binos. 10x50, 16x50, and 20x50. They all look like the are made by the same company but sold under different names. The 16x50 suffers from a slightly marked prism which spoils the view on that side. Can I put the prism from the 10x50 into the 16x50 as they are better to use.

[JamesF]

I'm not sure there's any way to answer that accurately

It's possible that prism pairs could be replaceable and interchangeable between models, I guess, but there's no reason to believe they would be. I know in some binoculars they're glued in place and even if you were prepared to re-glue them you might have a nightmare of a time aligning them properly.

James

[allcart]

I've already had the 16x50's apart. Each prism is held in place by metal plate and a screw. Once the screw is removed the metal plate can be removed and then the prism. No glue involved that I could detect. The collumation was way out so I took them apart to see how the adjustment was made. It was then that I noticed a mark on one of the prisms.

[BinocularSky]

Can I put the prism from the 10x50 into the 16x50 as they are better to use.

If the prisms are the same size, yes. If not, even if it does fit physically, the optical path lengths will differ and focusing will be binocular hell. It will help (but not affect focus) if the prisms are of the same glass.

Lots of similar binoculars use the same prism assemblies, so it is quite possible that you'll be lucky.

Have fun!

(On the batphone with Tapatalk)

[JamesF]

Yup, it sounds possible then. I'd probably try cleaning the prism before moving it though, given that the potential is there to end up with two pairs of unusable binoculars

James

[allcart]

If it doesn't work James I can always just put them back together. These binos are not complicated in construction.

[Peter Drew]

If the mark is on the final exit face, probably the only place where it would show in the eyepiece, and it can't be cleaned off, it might be worth swapping the prisms around so that the mark is further inside the train and then out of focus.

[allcart]

The problem seems to manifest itself as a diffraction spike on one side of a star at about the 2 o'clock position. I hadn't thought of doing that. I'll give it a go at the weekend and see if it makes any difference.

[allcart]

Took the binos apart again. The 2 prisms in each side look identical so have polished them and reassembled them. The mark that I thought was a scratch has gone. Just need to see some stars so that I can test them.

[allcart]

Quick update. The stars are out so I went out to check the view with these 16x50 binos. Well what can I say.... the view on the right side that I have serviced is staggering. The sky is a nice deep black and the stars are beautiful. The left side is somewhat dull and far less contrasty, so its back inside to service the left side and then collumate.

Stand back ! I'm going in.

[allcart]

Oh no !! Thats done it now. What have I done???

Andromeda is no longer a slight fuzzy patch seen with averted gaze. Its now a big beautiful fuzzy patch, easily spotted with direct gaze. The stars are better than I have seen them for weeks., partly due to a crystal clear sky, but mainly because I took the time to clean my optics and prisms. Collumating is a slight pain, but the gain is worth it.

Did I mention that these binos only cost about £10 from a charity shop. I have another pair of 20x50 that are going to get the same treatment.

[angusb1]

Nice work!

What model are the binos?

[allcart]

they are a very old pair of Prinz 16 x 50.'s with a plastic covering that has to be scraped off to reveal the prism adjusting screws. The 20 x 50's have the name 'Mark Scheffel' on them but are almost identical.

[angusb1]

Cheers, I have a pair of prinz 8x30s that are well out of collimation that I got from a charity shop for £6. I might have a crack at collimating them. Glad to hear yours are sorted now.

[angusb1]

Smartphone posting mistake