Priscopic Prism Company Scope and Mounts.

[Peter Laidler]

Unscrew the counter cell (the lens retaining ring) from the tube, tip the rear lens out, separate and re-cement is the way that I have always done it. But don't just do one lens, always do both

[Valleysniper]

RWDAVIDSON

There are 2 versions of the PPCo ocular assembly, see my strip down article and picture of the 2 different ocular assemblies I did here:

Milsurps - WW1 Periscopic Prism Co Ltd London Telescopic Sight Strip Down (by Valleysniper))

Sounds you have what I call the stepped tapered ocular assembly where the front lens is retained in a cell with eye ring held in at the rear with a ‘rolled over’ retaining ring. The rear lens is retained exactly same way in its cell. The 2 rolled over edges of cell are the convex side of lens and face each other when fitted. Sometimes there is also a separate spacer ring between cells but not in all.

First of all accurately measure the width of the cell you are to repair and record it. You will then need to carefully turn down outer edge rotating slowly in a lathe until you get down to the inner ring near to the edge until it falls off, BUT watch the lens does not fly out of housing and get damaged. You could do final turning down by turning lathe chuck by hand or using a hand crank, you could also hand file. After turning down you should be left with a step, if you are lucky the retaining ring will come out easily but not always, it is also likely the lens might have balsam from between lens elements that has squished out of elements and cemented lens to inside of cell. Warm the cell and lens with hairdryer on hottest setting and wearing gloves (not rubber) gently start pushing lens out towards rolled over ring side, effectively removing lens and retaining ring same time. Take your time and keep the cell and lens hot regularly checking you are pushing lens out squarely and equally, if you get up too much of an angle on lens try and get square again as you can easily chip edges of lens and Peter has just sold last set had made.

If all comes out successfully and lens has not fully separated I always mark edges of lens elements so when they are re-balsamed they are as left factory hopefully the 2 elements being optically centred by factory (although some PPCo scopes have some serious optical problems that are factory original).

To retain your freshly cleaned and bonded lens in its cell the retaining ring can now either:

A) Be carefully bonded in with clear epoxy obviously ensuring none gets on lens outer surfaces.
B) The stepped edge/retaining ring soft soldered and neatly finished.
C) Thread inside of cell and make a threaded replacement retaining ring, this is the best method but time consuming and costly unless can do yourself.

You will then have to make a spacer (or wider replacement spacer) to recover any lost width of the lens cell after your repair otherwise the rear lens cell will rattle in the ocular bell between it and front lens cell.

Hope all this makes sense?

[rwdavidson]

I have very carefully reviewed the dis-assembly and assembly article, it is a wealth of information. I have attached a photo of the scope for identification, and some closeups of the lens assembly. The rear most lens looks like it is missing some type of threaded ring? I can see what looks like a faint roll over line on the opposite side with a slight amount of solder showing. Is this the side I should remove in order to get the lens out? The innermost lens is perfectly clear, and I am somewhat hesitant to take it apart since it appers to be in very good condition.Attachment 37771Attachment 37772Attachment 37770Attachment 37775Attachment 37773Attachment 37774

[Valleysniper]

The threaded inner of outer lens cell with built in eyering (nearest eye) was for the engineering machinist to hold the part on a threaded holder whilst turning boring and threading. Its the opposite side of this cell you want to machine off the rolled over lip down to depth of inner retaining ring. Don't be tempted just to machine off very edge, come back in about 1 mm to 1.5 mm from very edge to stand a chance of removing all of beading over of outer cell edge to inner ring.

I cannot see from pictures posted any signs of solder on cell that needs repairing and I just removed one from one of my scopes to compare. If there is suggests repair done already, but looking at the degradation of the Canada Balsam bonding the 2 lens elements it's looks like its been there for almost 100 Years now.

Let us know how you get on.

[Badger]

T
I've just purchased "Sniping in France" as well, are there any other definitive works on WWI sniping that I should be on the lookout for?

Paul.

For those that want a great read, check the MKL for this book....

Milsurps Knowledge Library - Sniping in France 1914-18 (by Major H. Hesketh-Prichard DSO, MC.)

Regards,
Doug

[rwdavidson]

I will probably not be able to work on the lens this coming weekend - opening day of deer season here. I will be working on the lens weekend after this. I will take lots of photos as I dis-assemble the lens carrier and post them here.

[RobD]

I wonder if there is a lesser way of improving the crystallized and cracked balsam - if that is the main optical problem? One of the regular forummers was about to take apart a telescopic sight, found things a bit stuck, and used a solvent to try to loosen the balsam. Not sure which solvent. He forgot about it for a while, but when he came to look at it again, to his amazement the lenses were perfectly clear, and he could avoid dismantling the scope altogether. Would that make sense to try in this case?

[Peter Laidler]

Richard, can I offer you a bit of advice before you embark on your telescope project. Feel free to ignore it of course, but it is based on long learned experience............. It seems to me that you have two ocular lens assemblies, both of which are enclosed in roll-sealed cages. Just be warned that as soon as you take these apart (more later), separate, clean and re-cement the lenses and re-house in the cages, then you will need to refocus the graticle and then the image because your action will have changed the focal and optical properties of the lenses because you have effectively changed the refractive index of the double lens .

The next thing is this.......... The FLINT part of the double lens configuration is VERY hard glass and will crack or chip, externally or internally as soon as you look at it!!!!!!! Worse still, it can 'scatter' internally caused by internal previously unseen fault lines within the glass. So treat the lenses as gold dust, made from the finest unobtanium mined in the mountains of Utopia.

On a personal note, I wouldn't re-pack into roll-sealed cages but I'd adapt the ocular lens system to mimic the No32 Mk1 free floating lenses, using spacers to take up any side or end float.

If, like you, I hadn't attempted such a job before, I'd get a couple of cheap old telescopes off ebay to practice on

But just be VERY careful

[rwdavidson]

Peter:

Thanks for the advice. I only plan on repairing the rearmost lens. The inner lens still looks like new. Do you think that only repairing the outer lens will cause major problems?

My plan at the moment was to remove the roll over, remove the lens spacer ring, and then the lens VERY carefully. I have heard that alcohol will dissolve the old canadian balsam, but I certainly would like some advice on what / how to dissolve the old balsam.

I have some other old lens assemblies I can practice on with regards to dis-assembly and re-gluing for practice.

Richard

[TonyE]

Sniping In The Great War by Martin Pegler is a good book.

...if you like books full of errors!

Regards
TonyE