Binoculars Prismatic No5 repair

[bigduke6]

Thought it may be of interest to some, regarding a repair to a prism from a recent purchase, the first thing I do is look through the the wrong way, this can give an indication of a breakdown in the balsam or anything major in the inside.

These were ok apart from one side were the view was similar to looking through yellow frosted glass, a clue to the breakdown of the balsam.

I,m not going to teach anyone to suck eggs but a repair is very simple, just time and the correct jig or set up, here I,ve used what I,ve used on two other occasions so I know it works, if it was the ocular lens then its a bit more technical as this one (right hand side) is the one with the graticle , luckily this was in tact and no signs of any breakdown in the balsam.

First off a decent small screw driver set or a multi bit set is needed, without it its like ****ing in the wind...



First off is to remove the cover 3 screws and lift off gently (I say gently it may require some force) but there lies a copper plate underneath.



Remove the plate (sometimes this may be damaged due to a previous owner having a peak inside and not placing back correctly)

when removed the view is the prism itself with ocular lens and the securing bar, two screws and this is removed.




its a case of gently lifting the whole assembly out (this is in two parts due to the breakdown of the balsam.





Pic below is the two together with the spacer or securing plate? I gather this just gives more support, acts as spacer and enables the prism to moved in place or part of the original process of cementing the two parts together?



Next step is is straight forward, the two joining faces need to be cleaned and clear of any of the previous balsam, acetone or pure acetone nail varnish remover is the only stuff I know of, it will take some time but a warning here be sure to keep it away from the ocular lens.

Once cleaned, and clear it needs to be spotless the last clean of the two sides should be with a lint free cloth, also pays dividends to be in a relative dust free area (not possible were these were done) still specs of dust visible but its photo purpose only they were as clean as could be before cemented together.



The cement, there are modern cements that with a small amount of UV they will bond in seconds, but they don't allow for any mishaps and was told once there together they aint coming apart ? so use the tried and tested method and done correct will last our life time.

So the choice is simple Canadian balsam (it smells nice too, in fact the old crystallised balsam smelt as fresh the new stuff)



The next part is trying out the jig, don't even try without something basic as this, (I,ll come back regarding small ocular lens etc)



Its as basic as can be it positions the two together and the clamp secures the two and keeps the sides even, you need multi hands for this I can only say try before you use the cement, the actual pics show the two parts cemented and secured, the plate is below the two sides and in front of this (just visible) is two craft knife blades as spacers.

Its hard to apply and show the steps in pics of the cementing process, to get the idea there are a few clips on You tube IIRC, you only need two or more drops and put the two together and your pushing them together to form an even clear layer between the two, careful with excess also as you can end up cementing everything together, I will try and find a drawing of the the other jig I have and also show the correct position needed for the prism.

One thing is patience, as it can take over a few weeks and leave in a warm environment (but no direct sunlight), so avoid your favourite work or hobby bench.

I will post the rest in part two. Any of the experts please chime in to correct any mistakes.

Information

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[browningautorifle]

Well done...

[Trap4570]

Very interesting and informative. I have an old Bausch & Lomb Balvar scope that the glue used to secure the lens together has degraded and shows spots. Can this be used to repair the scope? Once the bottle is open will it seal back without becoming hard like super glue does?

[bigduke6]

Trap4570, it should do the trick but does take a long time to cure, just noticed my mistake in post #1, it should state well over two weeks, yep it will seal and not harden but I would advise to fill the pipette before you replace it and wipe the threads of the bottle.

To the get the lens apart u need heat, either leave on a lamp and slide the two parts apart or can use a paint stripper gun (one of the electric ones), its a bit off putting when using the gun as it sounds like cracking glass as the balsam expands etc.

[desperatedan]

Looks great Geoff - is the Bière Supérieure an important part of the repair kit and at what stage is it required?

[bigduke6]

Looks great Geoff - is the Bière Supérieure an important part of the repair kit and at what stage is it required?

It was one of the rare occasions it was warm in the workshop, plus had shifted the best part of 6 ton of soil that day, so some light refreshment was needed, but its not part of the repair process and not required but optional (£3.45 for 10 bottles in Aldi)

[Peter Laidler]

Can I respectfully suggest that instead of lint free cloth or ANY cloth, you use the cheapest paper kitchen towels you can. These don't(?) contain any of the usual chemicals that the super-dooper expensive and all singing and dancing towels contain. They're also as lint/debris free as it's possible to get. The good part is that because they're so cheap you can simply tear-off and use as many as you like. I have been known to use half a roll doing a pair or No2 binos or a telescope.

I also basically clean down the optics on the bench with cheap industrial grade methylated spirit and then before assembly wipe clean with pure M.S which leaves an absolute surface.

[bigduke6]

All suggestions welcome Peter (I,m just an apprentice in these things) I do use kitchen towel, but use something similar to the little strip you get when you get a new pair of glasses, managed to get quite a bit of the stuff and use it on the last clean, don't know but always thought it lint free ? as regards to Meths does this breakdown the old balsam or is just for cleaning? I gather M.S is pure Meths ?

[Surpmil]

"Product from Canada". Hmm!? More likely product from Celestial Kingdom methinks. And that label hath a lean and hungry look that says the same!

[Peter Laidler]

Methylated spirit will break down SOME forms of Canada Balsam in my experience. But why it won't break down some others that are clearly Canada Balsam, heaven only knows. Best for taking it off is old carbon tetrachloride as taught to me in the 60's but, alas, now banned. Trichlorethylene is a good second best but MUST be wiped off with surgical/pure MS before assembly to clear any residue.

M.S. is just my abbreviation for Methylated spirit. Just to reiterate. I use industrial meths for general cleaning but before final assembly I clean all lenses, prism's etc etc with PURE/Surgical MS to be 1000% certain of cleanliness.

Occasionally you'll get a layer of balsam or other adhesive that you just can't get off a lens, generally around the edges! We used to use a piece of thin/.005" or so brass shim to gently scratch/scrape it away. The shim won't attack the glass.