COMPASS, PRISMATIC, Mk3 (by Peter Laidler)

:beerchug:

With thanks to Advisory Panel member Peter Laidler, a new article has been added to the Technical Articles for Milsurp Collectors and Re-loaders (click here).

COMPASS, PRISMATIC, Mk3 (by Peter Laidler) (click here)

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Article Extract .....

There has been a bit of interest on this forum about these prismatic compasses and the variations that have emerged since they were introduced in……….., well, whenever it was, they seem to have been around since, well, forever! Certainly since my time in the Army, first learning to read a map and compass as a Cadet at school in the early 60’s. They’re of some significance to the Lee Enfield story because the compass was a supplementary issue alongside the equally important binoculars and wristwatch for the snipers. While they’ve all changed slightly, they’re still very similar …... article continues in link shown above .....

http://photos.imageevent.com/badgerd...pass%20001.JPG(Click PIC to Enlarge)http://photos.imageevent.com/badgerd...pass%20004.JPG(Click PIC to Enlarge)http://photos.imageevent.com/badgerd...pass%20006.JPG

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Peter has added a personal request in regards to this article.

Note: If you have any questions or don’t understand something or my instructions are ambiguous then please ask on the forum and NOT by PM (Private Message). That way everyone will get the benefit of the question and answer.

Regards,
Doug

For those who weren't following it at the time, this article links back nicely to the following thread also abotu the MkIII compass.

Just got my MkIII Compass back from Trademark London

I forgot to say in the article but if you are going to replace ANYTHING on your compass, especially those odd missing screws, then dont forget to check that they are NON FERROUS. They must not contain iron. Only bras- like material will do. Otherwise the sensitive magnetic pointer will go haywire and you'll never meet that RV point in the desert in a hundred years!

I may be mistaken, but is the new Stanley G150 production not using aluminum housings now?

Nope, Maybe for the commercial world but these looks brass to me!

Fair enough, though this assumes UK MOD is still buying new Stanleys - they may be, I'm not sure?

OK, I just figured out what I'm talking about - lol. Stanley stopped making the 150 a few years ago and according the the SIRS website:

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The G150 Prismatic Compass, previously manufactured by W F Stanley, is now produced in the UK by SIRS Navigation Ltd.

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It is made of brass and always has been.

http://www.sirs.co.uk/G150%20Marching%20Compass.htm

Now on the other hand, the Francis Barker MkIII, of which the G150 was a copy, evolved into the M73 compass and is still made by Pyser, who now owns Francis Barker. I suspect Stanley got away with making the G150 as the patents have likely expired. Pyser also makes the M88 which is an aluminum M73, or in our way of thinking, an aluminum MkIII with tritium lights and no compass cardinal points engraved on the outside of the case.

From what I understand, Pyser considerd the M73 nearly indestructible, serviceable, and in essence it can be made to work forever given time, money and parts. The M88, on the otehr hand, they consider disposable once the kerosene leaks out of it.

http://www.pyser-sgi.com/productdeta...?ProductID=321

I have no idea if UK MOD uses the M88 or just the M73, MkIII and G150.

In terms of fluid, Stanley filled (and now SIRS Nav) their compasses with Isopropanol while all the Francis Barker and Pyser compasses used purified kerosene when new. I understand UK MOD practise is to rebuild the latter with Isopropanol when they come in for repair.

Thanks Peter...changed out my fluid, got rid of my air bubble. Thanks so very much.

Bouletbill and another have asked about doing the same thing with a pair of old No2 Mk2 or 3 binoculars. I COULD but to be really honest, once they're back together you'll need to collimate the two sides. This is because each side of the binoculars is in fact a prismatic telescope. You've all looked through a pair of cheap/rubbish binoculars where you see two distinct images and they'll never merge into one. At the same time they'll give you a severe brain or head ache. That's collimation error for you and you need a light box collimator to set the eccentric OG lenses to merge the images.

There is a way to do it by eye but it's hard learned knack and even harder to explain

The next 'problem' is that the reticle lines are etched onto an optical glass plate. So fine that they are almost invisible. So can you imagine the problems cleaning the plate, on both sides! It's difficult, even in a clean room...... The smallest spec of anything looks like a huge lump of coal

Too bad really, those binos can still be found for very reasonable prices.

They are VERY nice too. Tough and reliable, they'll take a lot of hard knocks. I'd just suggest that everyone get a pair, so long as they're complete. Even if they just stay in the chest

We received a message about Peter's article through our Contact Form from one of the thousands of unregistered guests who read the forums daily, which I thought I'd post here .... :thup:

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The following message was sent to you via the Military Surplus Collectors Forums Contact Us form by Steve Ince.

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The article regarding 're filling a prismatic compass' was perfect, and worked like i was a professional compass filler!!.

Thanks
Steve
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User Name: Unregistered

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Regards,
Doug

Thanks for that and the other complimentary comments. Someone did contact me to the effect that he made a simple evacuation/depression chamber in a screw-top jar by evacuating it and retaining the vacuum by using a vacuum pump that formed part of a polythene food bag evacuation and sealing system.

Ok if you're doing a load of them but methylated spirit is better for the run-of-the-mill single compass.