COMPASS, PRISMATIC, Mk3 (by Peter Laidler)

[Badger]

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)

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 .....

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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

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Claven2]

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

[Peter Laidler]

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!

[Claven2]

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

[Peter Laidler]

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

[Claven2]

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

[Claven2]

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:

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

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.

[newbieDAN]

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

[Peter Laidler]

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

[Claven2]

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