Hans Seeger, Militaerische Fernglaeser und Fernrohre, 2.5, pages 179-182
(without footnote p179)

 (page 179) As already mentioned above, in the First World War, military 
signal finder telescopes were developed for 'communication between pilot and 
battle line'.  Without doubt, these were also equipped with direction finder 
or observation telescopes.  We shall not dwell on these short-lived 
developments, though some details can be found in Schwarte (1920).

For communication between plane and ground, radio technique had been 
increasingly used during the First World War and later.  In spite of these 
developments, there existed in Germany shortly before the Second World War a 
number of military optical telegraphy instruments.  They are listed at the 
end of the chapter; they were made by Zeiss, and it is possible that there 
were further Zeiss models or similar models by other manufacturers.

At a high cost, similar direction finder telescopes were developed and 
improved in Germany for the Navy, they were in the tradition of the models 
from the First World War; which again demonstrated the especially high value 
of observation glasses.  Fig. 101 shows such a model.  The special 
characteristic of this field-glass is the filter discs, which can be moved 
into the light ray with the aid of levers.  (p182)  The large, disk shaped 
filter housings on the entry side give the glass its special appearance.  
The photo shows this rare Navy glass, and fig. 102 shows a complete 
'direction blinker' RP 40 with added D.F. 7 x 50 H.  For further details 
about this field glass, see section 4.3.2.

An instrument on the ships of the wartime navy served to signal, and to 
observe signals of the opposing lines.  The signal 'cannon' with revolver 
grip forms a rigid unit with the added field glass, which can be moved in 
the holding device in both horizontal and vertical directions.  Intensity of 
light and color can be adjusted; blue or white light can be chosen (with the 
lever at the backside of the 'cannon', which in position 'blue' pushes a 
filter into the ray path of the light bulb).  The intensity of light is pre-
chosen by a step switch, which can be found under the carrier for the 
'cannon'.

At the foot of the RP 40, there is a small bearing circle, which reads 
360 degrees.  The mounting for the Zeiss DF 7 x 50 H is attached to the 
upper side of the RP 40.  The case is made of wood and contains among other 
things a field glass mounting for the Zeiss D.F. 8 x 60H.  (The intended use 
of the D.F. 8 x 60 H is discernable from an adjuster plate (?) in the 
original transport case, which has the inscription: D.F. 7 x 50 on one side, 
and on the other side 8 x 60 H, see fig. 102 and 216.)  The signal is given 
by the 'trigger' at the pistol grip, and the light source can be observed 
through an observation window at the back side of the lamp housing.  The 
light ray is narrowly focused by an optical system.  The importance given to 
the 'direction finder blinker' can be gathered from the fact that in at 
least one case, this instrument was made unrecognizable in war photos.  
('Kriegsmarine facing the enemy', 1940, page 36.  In the magazine: 'Die 
Kriegsmarine', the same photograph was shown unaltered, see fig. 216 in this 
book)

There is no written information about the 8 x 60 shown in fig. 101, and 
no pictures or documentation - only the glasses themselves.  The marking 
'Carl Zeiss Jena' on one of the depicted 8 x 60s indicates a manufacturing 
date of sometime in the first half of the war, and the manufacturing mark 
rln on the other, of the same construction, indicates a completion date of 
1944/45.  The deduction that these models for use on top of the direction 
blinkers were the successors of the 8 x 60 H and 7 x 50 H is therefore 
plausible, but for the time being not provable.

For the Navy, optical signaling retained its importance.  Schwarte (1920) 
systematically describes the 'immense number' of signal instruments.  Under 
group c, field glass instruments are described, for example: larger flares, 
which 'at night, directed onto the clouds, made a signal traffic of 60 to 80 
km distance possible'.  The Signal flares and Blinkers, which we are 
discussing here, offer the advantage of being able to work in different 
directions.  They cannot be disturbed by the enemy and can hardly be bugged, 
and also motor noise and fighting noise cannot influence the sending and 
receiving of signals.  


Table 10: Signal Instruments, which are described in the company magazines 
(Carl Zeiss, Jena) of the years 1937 -1939.

From the documents of Roland Leinhos. The  text was taken from the factory 
brochures and abbreviated.  We shall not concern ourselves with these 
instruments, which are only listed here because they belong with the 
direction finder telescopes. (HK= Hefner Kerze (Candle), measure for 
intensity of Light, today's unit: = cd (Candela), 2 cd = 1.16 HK)


*A Triple strip.  See DIN 58 158 leaf 3.  This is a prism sector of a triple 
prism (corner cube reflector).  The main characteristic of a triple prism is 
the deflection of all incoming rays by 180 degrees.  It serves to control 
the direction of the direction finder telescope in regards to the flare.  It 
can be seen in fig. 100, left upper corner, as a long triangle, slightly 
covering the objective.  The prism of the triple strip is no longer present.


** To use both instruments, also called light speaking instruments, the 
following are necessary: microphone, earphones, and a (80/2) or two 
'increase boxes'.  Furthermore an extendable tripod of wood, with standard 
cogs.  The modulation of the light ray is accomplished with a small prism, 
which is moved mechanically in a speech-like rhythm.  This prism is 
connected to another prism.  'The small prism changes… all the time... its 
distance to the reflection area influences the reflection capacity of the 
first prism, so that the intensity of the exiting light ray bundle is varied 
according to the speech rhythms'.  For details see the bibliography, Koehler 
(1938) and Rollema (1985); also see page 174.