The Scherenfernohrs (SF) - Part I: Background

Background

There seem to have been a couple of different stereo binoculars used in German AFVs in WWII, but the SF 14Z that was normally used in the Jagdtiger was probably the most common. These optical instruments were a development of commercially available binoculars manufactured by Zeiss before the war. In Germany they were called "Scherenfernrohr" or scissors telescope (Zeiss called them "Relieffernrohre,"), but they were not a commercially successful product for the company when sold to the general public. An 8x20 model was offered from 1894 to 1906, and a 10x25 model from 1895 to 1908. This is probably the design that was later bought in vast numbers by the German military and used in both World Wars with little change.
Viewing an artillery barrage through the lens of the SF 14Z

Typically, these binoculars provided spectacular views of terrestrial objects, greatly magnifying the perception of depth in a scene as well as the appearance of modeled relief. They were also used as rangefinders in both wars by several service branches of most of the participants in the conflict, particularly the Germans. The smaller hand-held scissors periscopes were about 6x30 power, with objectives that could extend to 18 inches, and the usually included a folding hinge to reduce the overall length for transport. Larger tripod mounted instruments sometimes had 50mm objectives, very helpful for use at dawn and dusk, and these larger periscopes were the ones typically found in armored vehicles. The SF 14Z had a magnification of 10x, a field of view of 5 degrees, eye relief of 12.5mm, and inter-ocular distance of 57mm+ as stereo, and 58mm+ as periscope. Normally, the graticle in the right eyepiece showed 10mil squares with 2mil gaps at 5mil intervals. There was an interrupted cross at the center for the datum or aiming point. The graticle could be illuminated by an internal light bulb, and it also incorporated a small clinometer that was also graduated in mils. A wing nut on the bracket allowed the periscope to be elevated to a comfortable position for the commander.
From Seeger:

A slightly modified S.F. 14 Z Gi was built in the second World War for use in tanks. It had a small, removable forehead support and did not have a spirit level for measuring the angle of the terrain. In the
interior of the tank, there were movable arms with pegs to install the scissor telescope (we will not describe the successor to this instrument, the RWDF 10 x 50 developed by Zeiss Oberkochen in 1956/58
and delivered after about 1960.)

With a relatively small field of view, (87 m/1000m), an S.F. 14 Z delivered a precise and sharp image. One can recognize details and is given the impression of looking through a higher power telescope. This
excellent optical quality explains their frequent use, especially during the second World War. Therefore the following official communication from the war years is astonishing, and possibly the high command of the
Army may have been afraid that the German soldiers had not made sufficient use of their optics at night during the war.

General Army Communication of June 7, 1941:

'Use of binoculars and scissor telescopes at night. It is to be noted that at night, the distance of effective observation of the unaided eye can be doubled with the 6x30 binocular, and about tripled
with a 10 x 50 binocular or a scissor telescope O.K.H. (Ch H Ruest u. BdE), May 31, 1941. 79 ln4 (IIIb)'

A major problem for the S.F. 14, as for all scissor telescopes, was that of collimation: the length of the arms and the fact that they are freely movable (as the long arms of a lever), permits an exertion of very little force to slightly tilt the arms and therefore move the optical axes from parallel to each other. Because of the relatively high magnification, a fused image, (with no double image), can only be seen after a precise collimation. The rough treatment which a scissor telescope has to endure during its "life" means that a perfectly adjusted specimen is rather rare. Those which are aligned in both positions of use, (with upright arms and with outstretched arms), are indeed rarities. (The alignment of an S.F. is an unloved and thankless task even for the experts.) An important part of an S.F. is the reticle, which was mainly needed for target shooting at sight, for artillery measurements, and for estimating distance. The reticle is placed in the image plane of the ocular, so that the scale and the observed image could be seen at the same time, similar to the cross hairs of a rifle scope. During the first World War, there was a diversity of reticles; but the later reticles, of the Reichswehr and Wehrmacht, were mostly standardized. During this time, a new reticle was developed: the Gitterplatte [grid plate], initially used for special purposes. In the paper by Kaiser (1918), the 'well known grid-plate' is mentioned, and therefore some S.F.s were equipped with the grid plate during the first World War. The S.F.s with "existing" reticles were known as 'SF 14 Z', and the S.F.s with grid plates were named 'SF 14 Z Gi' (for 'Gitterplatte'). From the outside, the two models are indistinguishable. The grid plate, (see my following posts) was of such great benefit that during the second World War, it was used almost exclusively. The grid plate was the characteristic mark of the German S.F. of the second World War. From the Army instruction paper of January 1937, it can be seen (in the most beautiful language of officials), that the grid plate was generally built into new instruments only after this point in time:

'Scissor Telescopes 14 Z with Grid plate'. Scissor Telescopes 14 Z with grid plate can only be issued according to the availability of the new acquisitions. An exchange of the S.F. 14 Z without grid plate for those with grid plate therefore cannot be made at the present time. High Command of the Army, January 19, 1937, AHA/Fz (V).'

A reticle or grid plate alone is not sufficient to fulfill all requirements for use of an S.F. under front line conditions. To correct the angle of the artillery fire, the advance observer has to use his S.F. to transmit the position of the exploding shells in the form of angles of azimuth and altitude. To establish the angle of altitude, there is a so called "terrain angle measuring device" or 'angle of sight' adjustor mounted on the S.F. To measure in the horizontal direction, there is a measuring dial, which is an accessory placed between the tripod and the S.F. During W.W. I, flat measuring dials were used, but the Reichswehr and Wehrmacht only used high (drumlike) measuring dials. In the dark, the reticle of the S.F. could be lit through a small glass window by means of a little lamp. The attachment for the lamp is on the tube of right ocular. All markings of the reticle are etched in the glass, for superficially applied marks on the glass would not be visible in the dark when lit from the side. The power source was an accumulator or more frequently, dry batteries, which were stored in leather or tin battery containers.

Next: Technical Description and Operation