The Japanese height finder is a sell-contained stereoscopic optical
instrument used to measure both range and height on the principles of triangulation. It
is dependent upon magnification and base length, the two basic conditions which
serve to increase the stereoscopic sense of the observer. The greater the base
length of the instrument and the greater the magnification, the greater amount of
depth perception will be attained. This enables the observer to read with greater
accuracy the distance to targets of extreme range or height.
The Japanese instrument has a base length of 7 feet 2 1/2 inches and can
operate on only one range of magnification -- 20 power with a field of 2° 15'. Its
total weight is about 500 pounds and it disassembles into three major units: the
tripod, cradle and tube. These units are packed separately in steel containers for
transportation. The Japanese instrument has only an outer tube and optical bar.
In adjusting its measuring wedges, the Japanese height finder depends solely on
external targets of known ranges or altitudes. However, it has an adjusting lathe
of such construction and dimensions that when it is set about 50 yards from the
instrument it can be used as an infinity target. At night this lathe is rendered
useless so that it is necessary to adjust the height finder on a visible
astronomical body such as the moon or a star. These bodies being at an infinite distance the
measuring wedges are adjusted at their infinity setting.
b. The Wedges
There are two rotating and one sliding measuring-wedges, and a mechanism
for concerting the wedge to read either range or height during operation. The
correction wedge assembly is machined out of brass. It employs a system of
stop rings to control complete movement of the glass wedge.
c. The Optics
The main optics of the Japanese height finder are extremely small in
diameter so that the field of view is greatly decreased and the light transmission
reduced. However, the instrument contains all the optics usually found in
stereoscopic instruments, namely: 2 end windows, 2 end reflecting units, 2 objective
lenses, 2 erecting systems, 2 ocular prisms, 2 reticles, 2 eye lenses, 2 field
lenses, 2 rhomboid prisms, ray filters, height if image plate, correction wedge
and the measuring wedge assembly.
The optical bar, which contains the main optics, is made of a beautifully
finished stainless steel. The adjustments of the optics are difficult because of
their undesirable position in the optical bar. In many instances it is necessary
to completely disassemble the instrument and remove the bar in order to make
the necessary adjustments for satisfactory operation.
There is a simplified method of drying out the optics in the tube. There
are two plugs on either end of the tube through which dry air can be forced
periodically but not during actual operation.
The optics are of excellent quality but are believed to be of German
The Japanese method of tracking a target makes it extremely difficult for
the observer to get stereo-contact with the target. They have only one man
tracking in azimuth and elevation and he must operate both handwheels for
azimuth and elevation sitnultaneously observing through a simple metal open sight.
The handwheels are both located to the right of the operator and are only a few
inches apart. A small wooden box, used as a container for several batteries,
is mounted on the left side of the cradle. These batteries furnish the only means
of illumination for adjustment and operation of the instrument. The Japanese
height finder has absolutely no electrical connections whatsoever with other
instruments in the battery and the information found on the range drum is either
telephoned or signaled in some other manner.
The Japanese range drum is graduated from 400 to 20,000 meters. However, the
Japanese use the mil scale for orienting their instruments. A circular
mil scale is located directly below the tube in the center of the cradle, secured
with two small screws. These screws can be loosened and the scale slipped
until the desired reading is found. In the center of this scale is a large handwheel
connected to the slip clutch plates which must be loosened through the action of
the handwheel in order to slow the instrument; it must then be retightened to