The examination of a German sighting telescope TZF 5b manufactured
by L. Leitz, Etzlar, and taken from a German Mark IV tank, where it was used
for the coaxially mounted 75-mm gun and the 7.92-mm machine
gun 34, revealed the following particulars:
|Length|| ||32 in|
|Diameter of objective (mounted)||23 mm|
|Diameter of eye-lens (mounted)||48 mm|
|Maximum elevation of telescope||+36°|
|Maximum depression of telescope||-22°|
b. Optical Constants
|Diameter of effective aperture of objective|| ||14.5 mm|
|Diameter of exit pupil||6.0 mm|
|Field of view (angular extent)||23.5°|
|Apparent field (field x power)||56°|
|Eye relief (1) mechanical||21 mm|
| (2) optical||30 mm|
|Plane of entrance pupil||48 mm|
|Axial light transmission||20.1%|
|"Veiling glare" index||14.5|
"Eye relief" refers to the distance between the eyepoint and (a) the eyepiece
mount (mechanical) or (b) the eye-lens (optical).
The "veiling-glare index" is a measure of the amount of scattering of the
light in its passage through the telescope, (in other words, the loss of
contrast in the image) and is a function of the optical design and the cleanliness of
the glass surfaces. A clean binocular usually has a value between 1 and 2, while a
value of 5 gives a noticeably misty appearance. It is probable that the
high veiling-glare index of this telescope is inherent in the optical design, involving
as it does some 30 air-glass surfaces.
c. Optical Performance
The captured sight was tested for optical performance with the following results:
With focus adjusted to give the best possible performance at the center of the
field of view, definition was good over an angular field of 8 degrees and
fair over a field of 15 degrees. Definition near the margin was poor. Eye freedom
was found to be good, and correction for color, curvature, and
d. General Construction
The telescope, which is of the fixed eye-piece type, consists of three main parts:
(1) Part one, (which moves with the gun) includes the objective (with protecting glass), the
graticule, and a single-reflecting prism. The objective is arranged in a tube (6A) (see accompanying
sketches for numbered references hereinafter) mounted on the front half of
the graticule box (4A), and the prism in a casing behind the graticule box.
(2) Part two includes the eye-piece and a second single-reflecting prism, which are
mounted in a stationary eye-piece tube (2A) fixed to the turret of the tank.
(3) Part three includes a double reflecting prism, which is arranged in an
offset box (3A), and connects the optical systems of parts one and two. The
optical and mechanical hinge of the telescope is located at this part.
e. Optical Hinge
The single reflecting prisms on the pivoting ends of parts one and two transmit the
line of vision to and from the respective reflecting surfaces of the double reflecting
prism, through hollow tubes which form the bearings of the mechanical hinge mechanism.
f. Mechanical Hinge
The mechanical link between parts one and two is formed by a small, flat, steel
plate pierced near each end by two large circular holes. Short tubes projecting at
right angles on the fixed and moving sections engage with these holes, and form
two bearings, allowing the sections to move in a vertical plane relative to each other.
Gears fixed to each short tube mesh beneath the plate and equalize the
movement at each bearing point, thus forming a virtual hinge midway between
the two bearings. These bearings are adjustable by tapered, flanged sleeves, which
are threaded on to the projecting tubes, and which form the bearing
surface in the connecting plate. The tapered flanges on the sleeves can thus be
drawn by the screw thread into countersunk recesses in the plate and any slack
A light metal cover beneath the connecting plate forms the seal to
exclude dust from the bearings and gear wheels; an aluminum casting, containing
the double reflecting prism attached by screws, forms the outer cover.
g. Focusing Adjustment
The focus can be adjusted by rotating a milled collar (1A) on the eye-piece. This
collar bears a scale showing single diopters and is figured at zero with 5 divisions
on each side of zero, the + and - signs being also engraved.
h. Range-Setting Gear
Ranges are set on the sight by means of a range-setting wheel (6B) on the
left of the eye-piece. This range-setting wheel is coupled by a shaft
drive including two universal joints (4B) to the mechanism in the graticule
box which controls the relative positions of the graticule plates. A limiting stop
a spring-loaded brake (5B) are provided for maintaining the selected range setting.
i. Graticule Box
Two glass plates are arranged in the graticule box: a circular range plate
which is mounted to rotate and a plate engraved with sighting marks, which moves vertically.
The scales on the range plate consist of small circles, numbered, as shown in
the accompanying sketch, in hundreds of meters. The sighting marks on the
other plate consist of a central triangle with three smaller triangles on
each side of it. The row of triangles covers an angle of about 1 1/2 degrees
in the object space. A fixed transparent pointer (7C) (figures 3 and 4) indicates
the range on the scales of the range plate.
To set a given range, the range-setting wheel is rotated, causing the range
plate to revolve until the required range marking is opposite the pointer, and
causing the sliding plate to move up or down so that the triangular sighting
marks indicate a position of the field in accordance with the scale reading.
The range plate (1D) (figure 5) is carried in the center of a cam ring (2D) which is
rotated by a gear wheel (3D) meshing with a gear behind it. A radius arm (4D) rests
on the cam ring and engages with a vertical sliding block (5D), which is thus raised
or lowered on rotation of the cam ring. The block (5D) engages a block (3C) (figure 4) on
the vertical slide (2C) which contains the plate (1C) engraved with the sighting
marks. The block (3C) is kept constantly pressed against the block (5D) by a return
Some appropriate measurements of the relative positions of the central
triangle for various scale settings gave the following results. (The column
headed "position of triangle" gives the approximate angular distance between
the central triangle and the circle marking the scale setting.)
j. Adjustment of the sight
The sighting point can be adjusted vertically by turning a key (1E) (figure 5) and
laterally by turning a key (6C), (figure 4).
Rotation of the key (1E) causes movement of a transverse slide (6D) (figure 5), in
which the vertical sliding block (5D) is mounted, thus moving the block (5D) across
the block (3C) and hence raising or lowering the sighting point. A spring (7D) constantly
exerts pressure against the slide (6D) to take up any play or backlash.
Similarly, rotation of the key (6C) cause movement of a traverse slide
(5C) in which the slide (2C) is mounted. At the same time, the block (3C) moves
across the block (5D), giving a resultant diagonal motion, the vertical
component of which may have to be compensated by turning the key (1E).
Both adjustments are made to fit a square key and the housings are internally
threaded, presumably for dust caps, which however were missing in the sight examined.
k. Night Illumination
The mounting for the range-scale plate is drilled on the edge, so that the
scale can be illuminated by the bulb holder (8C) (figure 4) through a glass
window on the side of the graticule box. A variable shutter in the bulb
holder varies the degree of illumination provided.
A 10-mm armor plate (3B) (figure 2) is mounted behind the graticule box to
give added protection in the case of a direct hit.