Stereoscopic rangefinder

[Scott Smith]

A calculation can easily be done to get the length of the unknown sides which gives you the range. I'll have to remember the forumula.

Thanks alot!

A bit more advanced than I first thought...

The formula for the range is the tangent of the measured-angle, multipled by the length of the base of a right-triangle.

The wider the rangefinder the more accurate the range-measurements will be because of the fineness of the angular-measurement possible.

The rangefinder would thus be oriented perpendicular to your target, and the lenses adjusted so that the images line-up, focus, or converge in the viewfinder, and that is an angle that is determined by the range to the target.

Rangefinders are very important for Flak because it might take 25 seconds for the shell to reach the target's altitude and the fuse has to be timed accordingly, depending on the height and distance of the incoming aircraft.

Also, rangefinders are used for machine guns and anti-tank guns. If you know the range to the target, you can calculate how high you will have to aim to allow for the bullet to drop by gravity in the time that it takes to get to the target, given the specific ballistics (velocity and aerodynamics) of the projectile.

For example, if your target is 1500 meters, you can set the elevation for your MG 42 machine gun's aiming-point from its mount to impact perfectly inside an oval-shaped zone. Without a rangefinder, you would have to guess from experience or "walk" your machine gun's aiming-point into the target-area using tracers (preferably before the battle).

Machine gun and rifle bullets can easily impact as far as three kilometers from the firing-point. In static warfare especially, stray bullets cause a lot of casualties in "rear" areas.

[Alter Mann]

I had an opportunity to find out, and didn't take advantage of it. While I was an M-60A1 TC I worked with a man that had been a TC on M-48s. Not sure what model, but they used the 'flying geese', or stereoscopic, rangefinder. The M-60A1s used an 'optictical coincidence' range finder.

As I remember it, and this was NOT last week, there were three 'V's in the sight, as well as the target. You cranked the ranging knob until both the target and the center 'goose' were clear images. Mechanical linkages ran to the ballistic computer to provide super-elevation, or you could read the range off a scale above the knob. Then you shot and hoped for the best.

There were several thing wrong with this system, and the US eventually gave it up. Suppose you have bad vision or diabetes which affects your vision differently on different days, or one of your crewman punches you in the eye? You shoot all over the place, waste ammunition and get dead.

Optical coincidence is different. It only requires one eye. The images from the two range finder housings are combined on a mirror. You crank the range knob until the two images form a single sharp image. The ones on the M-60A1 were supposed to have compensation for temperature built in. They definitely worked for me.

There are hazards with optical coincidence, though. While I was in Germany, knowing that the most common cause for a miss was an inexperienced TC, I spent hundreds of hours ranging to targets. When I got out, I realized that I had a visual problem. My optometrist told me that I had 'self-induced ambliopea'. In other words, my brain didn't accept input from my left eye, in my case. Hmmmm . . . Well, the way that the range finder was built, the headrest would only allow you to look through the eyepiece with your right eye. Your left eye was left looking at a white painted steel plate about 1.5 inches away. Anyone else out there been through this? I eventually got over it.

[Xavier]

how a naval rangefinder works
from: http://www.bismarck-class.dk

http://www.bismarck-class.dk/miscellane ... nding.html

best regards

Xavier
Instandsetzungtruppfuhrer

[Alter Mann]

Very nice illustration. This reminds me very much of the way that the optical coincidence range finder in the M60A1 worked, except that the image of the target was not split. We actually saw two images of the entire target, one slightly dimmer than the other. When the ranging knob was cranked the two images would either move closer together or farther apart. When the two images coincided exactly, the range was correct and could be read in a window above the ranging knob, also, if the linkages and ballistic computer were working, the super-elevation would be automatically added to the gun elevation. The gunner used a simple crosshair sight when the range finder was in use and it did not show the range to the target or move when the range finder solution was added to the lay of the gun, so all the gunner needed to do was keep the crosshairs on the target and the probability of a hit was high. The TC's sight in the rangefinder was just like the gunner's except for showing two images of the target if the range was not correct.

I used to be pretty good with an optical coincidence range finder, but I just took the test for stereoscopic vision and failed miserably. I doubt that I would have been any good as a TC in an M-48 with the 'flying geese' type stereoscopic range finder.

[Alter Mann]

Very nice illustration. This reminds me very much of the way that the optical coincidence range finder in the M60A1 worked, except that the image of the target was not split. We actually saw two images of the entire target, one slightly dimmer than the other. When the ranging knob was cranked the two images would either move closer together or farther apart. When the two images coincided exactly, the range was correct and could be read in a window above the ranging knob, also, if the linkages and ballistic computer were working, the super-elevation would be automatically added to the gun elevation. The gunner used a simple crosshair sight when the range finder was in use and it did not show the range to the target or move when the range finder solution was added to the lay of the gun, so all the gunner needed to do was keep the crosshairs on the target and the probability of a hit was high. The TC's sight in the rangefinder was just like the gunner's except for showing two images of the target if the range was not correct.

I used to be pretty good with an optical coincidence range finder, but I just took the test for stereoscopic vision and failed miserably. I doubt that I would have been any good as a TC in an M-48 with the 'flying geese' type stereoscopic range finder.

[TommySoelbergDK]

Hi
A litle something from US book, on German WW2 equipment.
TS

[Cool-E]

I have an R36 rangefinder and I have not figured it out yet. I have an English translation of the manual that I could scan and email to you. The translation is a little awkward, but let me know if you are interested.

[tommy303]

Stereo Rangefinders worked a little differently from the incidence and coincidence types. There were several types of stereo rangefinders, the earliest being one without moving parts. As has been stated, the user must have proper stereo eyesight. In the early Basisgeraet, the operator would look through his binocular type eyepieces and would see two images of the target. He had to concentrate to merge the two into one using just his eyes and brain. When he had focused properly there would be one clear image of the target, magnified and in 3-D. A string of numbered posts ran across his field of vision and appeared to receede into the distance. It was his job to see which numbered post appeared to be clearest and at the same distance as the target image. This was the correct range post.

A second type, utilized a grid-like reticle pattern with an aiming mark on the centre horizonatal grid line. Once the operator had focused on the target he ajusted the rangefinder for azimuth and elevation to centre the aiming mark on the target. He then used a handwheel or adjustment knob which when turned would appear to move the grid pattern closer or farther away. The hand wheel actually operated a rotary prism within the instrument, and he had to judge when the middle horizontal line of the grid and its aiming mark appeared to lay at the same range as the target, being neither short of or beyond it. The range could then be read off the scale next to or around the handwheel or knob. The other grid lines would appear to be closer and farther away. These were spaced so as to represent increments in range should a shot fall short or over the target. Depending on the calibration, they could be in 100 to 400m increments, and provided a quick reference for over or short bursts.

Yet another type used a coloured Wandermark in the form of a +, triangle, or diamond. The operator, when he had focused on target, would line up the sharp coloured aiming mark, then turn the hand knob until the ghost image of the Wandermark merged the the solid image. When merged the range could, again, be read off a scale. This type typically had in Flak work, a series of horizontal lines of diamonds in the reticle pattern to aid in adjusting running time for fuzes as well as making slight corrections in azimuth.