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Discussion Starter #1
Come on, admit it, we all love gadgets, especially gadgets that relate to our hobbies.

My hobby is long range shooting. So when I got the opportunity to get a coincidence rangefinder a few years back I just couldn't pass it up.

This unit is Swedish Military surplus and is designed to range to 1,500-meters. It comes in a wicked rugged case and has all kinds of widgets and gee-gaws to mess with.

This rangefinder uses a single eyepiece and two lenses facing forward. It can be utilized in either a horizontal or a vertical mounting.


Two prism wedges which when aligned result in no deviation of the light are inserted into the light path of one of the two lenses.


By rotating the prisms in opposite directions using a differential gear, a degree of displacement of the image can be achieved.


Once the two images are aligned (said to be in coincidence) the range is determined by simple triangulation.

The range in this case is: 181 meters
I've checked the accuracy with my laser rangefinder and this unit is spot on +/- 2 meters depending on operator skill.

It's also got a dandy mil-scale built into the base.


Believe it or not this unit actually has some advantages over a laser rangefinder. With this unit all your measurements are completely passive and without any emissions. Additionally this unit will give you a range to a "bird on a wire". Try that with a laser sometime.
 
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Discussion Starter #2
FWIW, the rangefinder was invented by Bradley A. Fiske (rear admiral, USN). He was born June 13, 1854 in Lyons, New York.


Since I'm on a roll here, did you know that Hiram Berdan (inventor of the Berdan primer) was born September 6, 1824 in Phelps, New York?
 

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Cool toy, what did it cost you?
 

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You can't beat the stereoscopic rangefinders. Never run out of batteries and if you run out of bullets you can still defend yourself with it. lol
 

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FWIW, the rangefinder was invented by Bradley A. Fiske (rear admiral, USN). He was born June 13, 1854 in Lyons, New York.
It makes sense that the Navy invented it for use on warships with large cannon. Kevin, your ammount of knowledge never ceases to amaze me. Thanks for sharing!
 
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Discussion Starter #6
You can't beat the stereoscopic rangefinders. Never run out of batteries and if you run out of bullets you can still defend yourself with it. lol
Let me pick a nit here; this devise is a coincidence rangefinder not a stereoscopic one.

Stereoscopic rangefinders are entirely different, although externally they resemble coincidence rangefinders except for the fact that they possess two eyepieces. It is essentially a large stereobinocular fitted with special reticles which allow a skilled user to superimpose the stereo image formed by the pair of reticles over the images of the target seen in the eyepieces, so that the reticle marks appear to be suspended over the target and at the same apparent distance.
 

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Hey, how does it work? Could you tell us more about it please?
 

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Let me pick a nit here; this devise is a coincidence rangefinder not a stereoscopic one.

Stereoscopic rangefinders are entirely different, although externally they resemble coincidence rangefinders except for the fact that they possess two eyepieces. It is essentially a large stereobinocular fitted with special reticles which allow a skilled user to superimpose the stereo image formed by the pair of reticles over the images of the target seen in the eyepieces, so that the reticle marks appear to be suspended over the target and at the same apparent distance.
Ohh. I see.. Is there an schematic on how the optics work? .. that's interesting.
 
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Discussion Starter #9

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Holy poop! The principle is so simple!
Must be some really fine gears in there.

So theta (A) is calibrated to the gears/indicator. Adjacent side is constant (from M1 to M2) The rest uses trig to estimate the range? Gears turn prism's at certain angle which is calibrated to the range indicator?
 
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Discussion Starter #12

Holy poop! The principle is so simple!
Must be some really fine gears in there.

So theta (A) is calibrated to the gears/indicator. Adjacent side is constant (from M1 to M2) The rest uses trig to estimate the range? Gears turn prism's at certain angle which is calibrated to the range indicator?
Yep, pretty much.

The side between the prisms is the "base" length. The longer the base length the more potentially accurate the device will be at longer ranges. Because the base length in my gadget is so sort it'll only work out to 1,500 meters.


This bad-boy is good to the horizon.
 

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That thing is huge! The navy used some even longer for the firing control command.

I wonder if you can see the range on this one with the "coincidence" one? lol.

 
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