Protector scopes

[Mrs Vampire]

Have all the bits made now .

[BCA]

I recall from my work with rock thin sections that Canada Balsam was used because the index of refraction was the same as glass. Differences in the index of refraction between different layers of glass or other substances would cause optical problems.
I'm pretty sure that the M3 protectoscopes look the same as the ones for the M5 Stuart and M20/M8 armored cars but I don't have a Stuart M3 book to confirm: Gina: Do you have a part number from your M3 book.
Finally, it may be that much of the periscope effect is from internal reflection within the prism, not from mirrored surfaces.

[Mike Cecil]

Hi Brian,

Interesting, and you are probably dead-right, but I don't think, as a student, I ever really concerned myself with the 'why' because I detested the hours of hand-grinding rock sections with Al powder when I could have been sinking beers or waterskiing!! Especially as the professional slide-maker in the Dept had all this automatic section-making equipment - and here we were 'learning' to make slides the hard way. I think it was my metamorphics lecturer's method of showing us who was in charge .... no wonder I majored in sedimentology and fluvial dynamic systems!!

Mike

[Mrs Vampire]

Hi Brian

I suspect the pistol port protectorscopes in the M5 etc are the same. The drivers and gunners protectorscopes in the M5 etc are quite different to the Stuart Drivers and Bow gunners scopes.

The pistol port scopes I cast are optically perfect if I put in enough work to flatten them of and polish them . The issue is that I have no desire to put in the twelve to fourteen hours necessary to do to the six pistol port scopes when I can pay sixty dollars and get acrylic sheet professionally cut and polished.

The drivers and gunners periscopes on the M5 etc are all standard 346 https://www.marstar.ca/dynamic/produ...roductid=82590

of which the Stuart had One up until the late production M3A1s which had two in the turret .

The pistol port Protectorscopes are quite different and so far as I can find unavailable.

The M3 turret had a direct vision "peep" hole system that consisted of a thick piece of flat glass. The later M3 hybrid and M3A1 turrets had a periscope like device instead.


The driver and Bow Gunners Protectorscopes are made up of two mirrors and two windows all of which are separate components and separately replaceable .
I don't have part numbers for any of the components either for Pistol ports or front hatch scopes.

[BCA]

Gina; In your figure sheet 2 of 4, is item A, "glass". I am pretty sure this is an item that have NOS: mine are plexiglass, 5-7/8" long, 3/4" thick, maximum width 2-1/4" with the polished faces being 1-5/8" x 5-7/8". They are different than the glass pieces that you posted earlier in photographs. PM me for more info or with an email where I can send you a photo.

[Mrs Vampire]

Progress on the Pistol Port Protectorscopes.

I rate the clarity at around 85% . I can see through them but not well enough to read my computer screen. I can certainly recognize someone at a distance of twenty feet though.

the first two are pictures with mirrors attached the third the extrusion I had made . It all looks remarkably clear but viewing acrylic sheet coupled with the slight distortion of the two polished faces means a less than optically pure result.
It is good enough for a view port in non combat situations and the costs of getting an optically perfect scope are not worth it .

So that's my limit on these tricky gadgets.

[Mrs Vampire]

I have now assembled my prototype using super glue...

I was advised against this but I threw caution to the wind.

Clarity is improved to near perfect when the entire face of the mirror is covered and all air bubbles excluded.

The suggestion of Canada Balsum would also be a very good fix...but I am impatient and the only supply is from E-bay

There are also a number of UV activated lens glues available but I have no experience with them and they are expensive when I consider the number of mirrors I have to mount.

The issue it seems is the distortion caused by the gap between the mirror and the prism. I worked it out and light has to penetrate fourteen surfaces from object to eye....lots of opportunities for distortion.