M38 Hollow Core Scope Project 2016 - Bulldog44

[MoSc0ut[TK]]

I was looking at surplusshed.com. They had some prisms, but I will have to pull mine out to see if it's a match.

Brian already did the work for you!

*update. Just checked that site you mentioned and they have no twisted right angle prisms. Bummer.

 

There are a few called 90 degree right angle prisms which, based on the description, may do the same thing......

 

 

 

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Edited September 27, 2016 by MoSc0ut

[Twnbrother]

I am reading some stuff that calls the two prisms in the M38 a Porro abee Prism. This might help in the research.

 

http://www.edmundoptics.com/optics/prisms/specialty-prisms/experimental-grade-specialty-prisms/3561/?print=Screen

 

A Porro-Abbe prism is sometimes called a double right angle prism. Two of them are used to make an erecting system for telescopes and some models of binoculars. One of these prisms can be used to bend an image 90° and rotate a vertical image horizontally.

Edited September 28, 2016 by Twnbrother

[MoSc0ut[TK]]

I am reading some stuff that calls the two prisms in the M38 a Porro abee Prism. This might help in the research.

 

http://www.edmundoptics.com/optics/prisms/specialty-prisms/experimental-grade-specialty-prisms/3561/?print=Screen

 

A Porro-Abbe prism is sometimes called a double right angle prism. Two of them are used to make an erecting system for telescopes and some models of binoculars. One of these prisms can be used to bend an image 90° and rotate a vertical image horizontally.

That's the one! Now to locate one with the proper dimensions..... Great work!

 

 

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[count chocula]

I am reading some stuff that calls the two prisms in the M38 a Porro Prism. This might help in the research.

 

Porro prisms are similar to right angle prisms. Porro prisms are used for a 90° light path bend by using the hypotenuse face of the prism rather than the leg faces. This configuration produces a right-handed image since two reflections occur. The incident ray's direction is reversed when using a porro prism since the object enters and the image exits the same face.

 

I've searched extensively for these prisms. They are sometimes called Porro-Abbe prisms. They seem to be nearly impossible to find. Several websites formerly sold these (e.g. edmundoptics), but have recently discontinued them. 

 

 

Some Russian company still has them on their inventory, but they haven't responded to my emails...

 

I even went so far as to design a 3-d model of the prism that is needed for this scope (a "12mm hypotenuse Porro-Abbe prism"). I had them printed in an "optically-clear" resin by a 3-d printing company for only 10 bucks, but even after lots of polishing, I'm not sure they are really clear enough to work properly. They fit very well into the scope I bought from Brian, but the image seen through them is a bit blurry. Also, the prisms used in the moisin nagant scopes must have had mirror coatings on the hypotenuse (maybe on other surfaces, too). I've not been able to find a good way to coat a single surface of a resin prism. If anyone wants a copy of the stl file you are welcome to it.

 

Here's a picture of the 3-d printed clear resin prisms before polishing.

 

 

I really wanted this to work, but this is going to take a lot more effort, I think. If anyone finds a good solution, I will take two, please. 

[MoSc0ut[TK]]

I've searched extensively for these prisms. They are sometimes called Porro-Abbe prisms. They seem to be nearly impossible to find. Several websites formerly sold these (e.g. edmundoptics), but have recently discontinued them.

 

 

Some Russian company still has them on their inventory, but they haven't responded to my emails...

 

I even went so far as to design a 3-d model of the prism that is needed for this scope (a "12mm hypotenuse Porro-Abbe prism"). I had them printed in an "optically-clear" resin by a 3-d printing company for only 10 bucks, but even after lots of polishing, I'm not sure they are really clear enough to work properly. They fit very well into the scope I bought from Brian, but the image seen through them is a bit blurry. Also, the prisms used in the moisin nagant scopes must have had mirror coatings on the hypotenuse (maybe on other surfaces, too). I've not been able to find a good way to coat a single surface of a resin prism. If anyone wants a copy of the stl file you are welcome to it.

 

Here's a picture of the 3-d printed clear resin prisms before polishing.

 

 

I really wanted this to work, but this is going to take a lot more effort, I think. If anyone finds a good solution, I will take two, please.

These ones may work: https://www.optotronics.com/proddetail.php?prod=p-0014 they are 16x8mm only 1mm off of the original specs. The lenses from the monocular should be compatible with these if what I'm reading is correct.

 

......and crap. Out of stock!!

 

 

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Edited September 28, 2016 by MoSc0ut

[MoSc0ut[TK]]

Have you tried these guys?

 

http://www.optocity.com/prism-reflective.htm

 

They have an inquiry form to see what it would cost for them to be made and it looks like they may be U.S. based. But custom usually = $$$

 

 

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[count chocula]

Have you tried these guys?

 

http://www.optocity.com/prism-reflective.htm

 

They have an inquiry form to see what it would cost for them to be made and it looks like they may be U.S. based. But custom usually = $$$

 

 

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I did, actually. Here's what they sent me when I asked for a 12mm hypotenuse Porro-Abbe:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thank you very much for your inquiry. We have Porro-Abbe prism, 14mm hypotenuse, also we can custom make Porro-Abbe prism, 12mm hypotenuse. Please let me know what qty. are you looking for? Material BK7 or Fused Silica, coating?

 

Best Regards,

 

Tom Zhang

Manager

Optocity

8900 Columbine Dr.

Raleigh, NC 27613

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

I asked for a quote for the 14mm hypotenuse Porro-Abbe prisms they had in stock (I figured it would cost more to have them make 12mm prisms). They quoted $45 per prism. 

 

[MoSc0ut[TK]]

I did, actually. Here's what they sent me when I asked for a 12mm hypotenuse Porro-Abbe:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thank you very much for your inquiry. We have Porro-Abbe prism, 14mm hypotenuse, also we can custom make Porro-Abbe prism, 12mm hypotenuse. Please let me know what qty. are you looking for? Material BK7 or Fused Silica, coating?

 

Best Regards,

 

Tom Zhang

Manager

Optocity

8900 Columbine Dr.

Raleigh, NC 27613

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

I asked for a quote for the 14mm hypotenuse Porro-Abbe prisms they had in stock (I figured it would cost more to have them make 12mm prisms). They quoted $45 per prism.

 

Holy moly! I guess the search continues.....

 

 

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[fieldmarshall]

We need to go into the prism grinding buisness !  .LOL

[fieldmarshall]

Wonder if they would be cheaper in volume???

[Bulldog44[TK]]

Yeah, the prisms seem to be pretty tough to find and too expensive to order. They would cost more than the plastic scope kit itself! 

 

I also tried ordering the tiny screws that lock the retainer rings and lens assemblies on the scopes but the local company that specialises in them here in Japan gave me a quote of $350 for an order of 300 or so. For such tiny screws they cost a whole lot so I have put off supplying them with my kits until I find a cheaper deal. 

 

I am still praying there is a honey pot of old scope parts lying around in some old vintage military depot, prisms and all! 

[fieldmarshall]

Yeah, the prisms seem to be pretty tough to find and too expensive to order. They would cost more than the plastic scope kit itself! 

 

I also tried ordering the tiny screws that lock the retainer rings and lens assemblies on the scopes but the local company that specialises in them here in Japan gave me a quote of $350 for an order of 300 or so. For such tiny screws they cost a whole lot so I have put off supplying them with my kits until I find a cheaper deal. 

 

I am still praying there is a honey pot of old scope parts lying around in some old vintage military depot, prisms and all! 

Going to have to bite the bullet,,, im working on having some made

[Bulldog44[TK]]

Going to have to bite the bullet,,, im working on having some made

Cool. Definitely keep me updated on this! I would be interested to purchase some if it helps with securing a large order. Edited October 6, 2016 by Bulldog44

[Troopacoola[TK]]

Love my number 5 scope kit. Very well detailed. This one's going on my son's Doopy's blaster which I am building for one of his Christmas presents.

Light and sound to be added.

 

 

 

Marc

[Bulldog44[TK]]

Awesome! Looks super cool with the lights. Honored to have one my scopes on such a great gift to your son. Thanks for posting this!

Edited November 18, 2016 by Bulldog44

[Chapaaz[501st]]

Hello mate how much are your scopes?

 

 

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[Bulldog44[TK]]

Hello mate how much are your scopes?

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PM sent.

[darthcue[TK]]

hey Brian i am interested in your scopes, how much?

[bpatneaude]

Hello would be interested in 2 scope kits, thank you

 

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[Twnbrother]

Brian this is impressive. Great work

[Bulldog44[TK]]

hey Brian i am interested in your scopes, how much?

Please read below! Thanks for expressing interest in my scope kits. Hope I can offer you a kit very soon.

Hello would be interested in 2 scope kits, thank you

 

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Please read below. Wow, 2 kits, I need to get these new molds made on the double! 

 

 Hi Kev, Brian and Ted,

    I am in the process of making new silicone molds for the M38 scope kit. I have some kits remaining but there are few parts on the kits that have issues I am not happy with. I tried recasting them this weekend and discovered issues with the silicone I was using. It shrunk a bit too much and the small parts do not line up as they should. I feel it would be better to start again at this point with new mold using a better silicone I found to be more reliable. If the kits cast as planned, they will be $30.00 plus shipping.   shipping cost is about $8.00-registered & tracking, this also includes the paypal fee. If you can wait I should be able to get the new molds made and parts casted within the next week or 2. Faster if I get free time after work.   I can offer you the kits I have in hand but consider them B or even C grade due to the quality of the smaller parts. PM me for the pricing if you wish to go that route. 

[Bulldog44[TK]]

Brian this is impressive. Great work

Thank you Mike! 

Edited November 21, 2016 by Bulldog44

[darthcue[TK]]

I will wait Brian..

 

 

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[Bulldog44[TK]]

I will wait Brian..

 

 

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Thanks for your patience. I will try to get the molds completed soon and update this thread when there is progress to report. Hoping the new molds produce more predictable, proportioned parts to make assembling these scopes trouble free. 

[pwhitrow]

Fantastic work mate, looking forward to owning one of these beauties