Question about Zeiss Turact with tickmarks and unusual eyepiece (1 Viewer)

I own a 1918 vintage Zeiss Turact 8x24 pair of binoculars that I inherited from a family member, and I am curious about a couple of features in it.

Question #1: Tickmarks.
On the bottom, the binoculars have two metal plates showing, respectively, a standing soldier and a soldier on horseback. These figures have horizontal lines ("tickmarks") that start at zero at the top of the head in both figures, and end at 1300 for the feet of the standing soldier and at about 1800 for the hooves of the horse. (See http://home.comcast.net/~dapena/binoculars/tickmarks.jpg ) Since these binoculars were designed for military use, I suspect that the tickmarks serve to estimate the distance to a standing person or to a person on horseback, but I can't quite figure out how the method worked. The tickmarks are spaced at the same distance apart for every 100 units. All the methods that I can speculate would require a non-linear scale, so they don't fit.

Question #2: Eyepiece.
The right eyepiece has an extra lens that can be brought in by turning a little wheel on the eyepiece. (See http://home.comcast.net/~dapena/binoculars/eyepiece.jpg ) My picture shows this extra lens half-way into place. When the extra lens is in place, the image stays as sharp as before, but you now see an equally sharp ghost image next to the original image, like with the mineral called "Iceland spar". (You see double.) If you rotate the extra lens, the ghost image rotates around the original image.

I would appreciate any responses to my questions #1 and #2. Maybe they are related??

Hello Suso,

The figures and markings work in place of a reticule, graticule in the UK. Let us say, that the user sees an upright and complete soldier, than the distance is the maximum. Should the observer see only a head, then it would be the nearest distance. Similarly, it works with the cavalryman on horseback. It works as a rough and ready rangefinder, suitable for setting the sights on a rifle. Such engravings and distance markings are typical of some early WWI French binoculars.

The extra lens may have allowed for examination of a suspicious object: rotating might have revealed camouflage or details. That is a guess.

Happy collecting,
Arthur Pinewood :hi:

Your binocular has a telemetric rangefinder in the right ocular. This device is fairly common on Huet 7X French WW I binoculars but I have never seen it on a Zeiss or any other German binocular. Your Turact could have been modified to accept it or, if factory made by Zeiss, it would be an extremely rare variation. The Turact, by the way, was a civilian model binocular, but was made during WW I and would certainly have been carried by some soldiers as a private purchase. Following are two links to my Flickr page showing how the rangefinder is constructed and works on the French Huet 7X:
1) http://www.flickr.com/photos/binocwpg/4855975772/in/set-72157623234405689
2) http://www.flickr.com/photos/binocwpg/4855353683/in/set-72157623234405689/

Pinewood:

Thank you. You provided much of the answer, and this allowed me to figure out the rest. The tickmarks and the extra lens are used in combination with each other.

The extra lens (Iceland spar) is not really a lens, it simply produces a double-image. So, for simplicity, from here on I will call it the "spate lens". If I look at a horizontal line with the binoculars, I can engage the spate lens, and then rotate it to a position such that I see only one line. But as I rotate the spate lens from that "one-line" position, I begin seeing 2 lines. A 90-degree turn of the spate lens produces the maximum separation between the two lines, and further rotation will start bringing the lines closer and closer together again.

I rotated the spate lens to the position that produced the maximum separation between the two lines. Then I hanged a ruler vertically from the ceiling some distance away from me. I then measured the distance from my binoculars to the ruler (about 5.20 meters), and also estimated the number of millimeters of vertical separation produced by the spate lens (7 mm). This means that the vertical angle produced by the spate lens was about (0.007/5.2=) 0.00135 radians.

At a distance of 1300 meters (the number on the tickmark at the bottom of the soldier image in the engraving on the binoculars), an angle of 0.00135 radians would produce a height of (1300*0.00135=) 1.75 m --roughly the standing height of a soldier: very nice fit!

So this is how the system works: If the spate lens' vertical separation (at max vertical separation) covers exactly the height of a 1.75 meters tall soldier, the distance to that soldier must be (1.75/0.00135=) 1300 m, which is what the engraving tells us.

Let's say now that the soldier is closer by, and that the spate lens' vertical separation covers only the height of the soldier's head from the top of the head to the neck. In the engraving, the height of the head is assumed to be [(200/1300)*1.75]= 0.27 m. The distance to this soldier must be (.27/0.00135=) 200 m. And that is what the engraving tells us too.

So you point at a far away soldier, and see how much of the soldier's body sticks out (upward) from the top of the head of the other image of the same soldier. If you see exactly the whole soldier on top of himself, then the soldier must be 1300 m away. If you see just the head sticking out from the top of the other head, the soldier must be 200 meters away. If you see the soldier sticking out up to his waist above the other image's head, the soldier must be about 600 meters away, etc.

Thanks a lot, I have been wondering how this worked for years!

[After writing the above comment, I noticed LPT's posting, which is right on the money, and adds some further interesting info:]

LPT:

These binoculars were probably captured by the French near the end of WW1, and they probably made the rangefinder modification. Everything fits! This hypothesis is further supported by the fact that the soldiers on the engravings seem to have French-style uniforms. They look straight out of Beau Geste.

Thanks, guys!!!!!!!!!