The German military 7 x 50 binocular.
Excerpts from section 4 of:  Hans Seeger. Militaerische Fernglaeser und 
Fernrohre in Heer, Luftwaffe, und Marine. Hamburg: Seeger, 1996.

Early 7 x 50 models.  Excerpts from  Hans Seeger, Militaerische 
Fernglaeser und Fernrohre.
4.1. Early Models and Marine Glasses with Roof Prisms.
...[page 285-6]  In 1899/1900, the first binoculars with 50 mm. 
objectives were constructed by Hensoldt, see fig. 67 (right).  The design 
of the ‘artillery-glass’ is not ideal for naval use, since the housing 
cover is a separate piece that is attached with screws.  Around 1903, 
Hensoldt introduced a new construction form for their Pentaprism models, 
which is characterized by a housing that is closed on top and therefore 
is more suitable for use by the Navy, see fig. 67, left; and fig. 116 in 
'Feldstecher'.  The ‘Marineglaeser’ in this Hensoldt series have the 
specifications 10 x 50 and 12 x 50.  Before they found real acceptance, 
they had to be taken off the market, because they infringed on the still 
valid Zeiss patent.  There was no 7 x 50 model in this Hensoldt series.
...It is difficult to be sure when the first 7 x 50 field glass was 
produced, and by which producer.  It was probably between 1905 and 1910.  
Considering that the glass available at that time had relatively low 
indices of refraction, it was probably either a Porro model with long 
focus objectives or a roof prism field glass.  Two models are possible 
candidates; the Porro II from Leitz (one of the 'Messingglaeser' [brass 
glasses], fig. 197), or the roof prism Noctar from Zeiss.  From Zeiss 
brochures, it can be seen that the Noctar (7 x 50) was already obtainable 
before large scale production began circa 1911, see fig. 196.
...The Noctar became the precursor for tens of thousands of Zeiss Marine 
binoculars.  A 12 x 50 model was also made with Abbe Koenig prisms, and 
W.W. I models of this glass with the ‘M’ marking of the Imperial Navy are 
known (one of these 12 x 50 specimens has housing covers of brass).  The 
third model in this series is a 10 x 50, and it can be supposed, but not 
proven by an appropriately marked specimen, that these were also used by 
the Navy.  All three of these binoculars have an identical appearance.
...Goerz did not want to be left behind, and at their plant in Berlin, 
shortly before or at the beginning of W.W. I, a 7 power marine glass was 
built, but with slightly larger objectives: the roof prism Marine Trieder 
7 x 52.5, see fig. 94.  [page 287]
...Around 1910, the first 7x50 Porro field glasses  were made, either the 
Leitz Porro II 'Messingglaesern' was first, or possibly the Porro I 
models by Busch, Rathenow or Voigtlaender, Braunschweig were made 
earlier.
...Busch first announced its 7 x 50 in 1913 lists, with Porro I prisms, 
called the 'Marlux', at the time as individual focus only.*  (*An old 
Busch catalog archived in Jena contains a remark by a Zeiss worker that 
is interesting: 'Center sharpness good; decreases towards the rim too 
fast and too much.  Our Noctar is far superior.')  A very early 7x50 
Voigtlaender Marineglas of Porro I construction is shown in Fig 219.
...However, the 7 x 50 that was the best known, was produced in the 
largest numbers, and made for the longest time, was the Binoctar from 
Zeiss, Jena.  This was to be built in many variations, became the 
standard Marineglas, and originated in the time between 1910 and 1914 
(see 4.3.)
...
...4.2.1.  Porro II Marine Glasses by Leitz
...[Page 289]  Before W.W. I, Leitz began developing a series of Porro II 
glasses. These Leitz Porro II models were successors to the unusual Leitz 
Porro I models, which were also used in the Imperial Navy, but which were 
only a temporary product at Leitz, see fig. 218.  This strange design had 
objectives that were spaced only a short distance apart, and probably did 
not meet with approval.  Not until years later did Leitz built larger 
Porro I models in the manner of the Binoctar, with the metal parts mostly 
of brass, and only the prism housings of aluminum (as was standard).
...Leitz worked on the Porro II design, and after 1907, built a series 
including a 7x50 of brass with leather coverings, see 197b.  The Leitz 
'brass glasses' established the Porro II models as a service glass for 
the Navy, where they were to serve for 5 decades.  The specifications of 
these Leitz glasses are: 7 x 50, 10 x 50 and 12 x 60.  Of the surviving 
examples of the 7 and 12 power models, about half have an 'M' and an 
Imperial crown, an indication that these models were used in the Navy.  
The 10 power model is frequently marked ‘Dienstglas’, an indication of 
military use, which of course includes the Navy.  In old pictures (see 
fig. 198), it can be seen that the 7 x 50 model was used on German 
submarines in W.W. I.
...Whether these high quality Leitz field glasses were sold on the open 
market is questionable; the civilian and military Leitz brochures of the 
years before 1915 do not include these models.  It is improbable that 
examples of these marine glasses were exported to other countries before 
the first World War. All three models appeared in the 1919 civilian 
brochures of Leitz, where they had never previously been listed.  Those 
glasses were probably left over from war time production.  In the middle 
twenties, the 12 power model disappeared.  From that time on, the 7 and 
10 power models were probably also offered with center focus.  As 
civilian models on the open market, these Porro II glasses remained 
available from Leitz until 1931-32, in both individual and center focus 
models.
...It is unclear whether the individual focus models, with aluminum body 
and hard rubber coverings, were also bought by the German Navy, which was 
then very small because of the treaty of Versailles.  In the third Reich 
the situation changed.  Field glasses were needed in great numbers 
because of the intense re-armament, and Leitz built several variants of 
the 7 x 50 models with Porro II prisms.  All models had an eccentric ring 
collimation to align the optical axes.  [page 290]  At the beginning of 
this era, the earliest of these marine models used upper prism housing 
covers of brass, attached in the usual manner and held in place by three 
screws.  Later, all metal parts of this model (which was produced until 
the end of the war), were were made of aluminum.  For another Leitz 
marine model, the prism housing cover was formed differently and fastened 
by screwing onto the housing, see fig. 199.  These models have cartridges 
for dessicant, which are inserted into the upper cover.  These 
cartridges, often used in the thirties and forties in military optics, 
are filled with water absorbing silica gel (see section 4.3), and prevent 
hazing of the optics after the entry of humidity.  If needed, these 
cartridges can easily be exchanged with special tools.
...At the end of the thirties and during the war, the 7 x 50 marine 
glasses by Leitz used coated optics (see section 4.3).  During this time, 
a special series of this model was produced, which used a different 
construction for the ocular.  This change was dictated by the partial 
rubber covering used on this model.  The exposed parts of the body of 
this 7 x 50 model were coated with a tough lacquer.  The only known 
examples of these rubber coated models are those marked 'beh' (E. Leitz, 
Wetzlar).  All have dessicant cartridges in the upper cover, see fig. 
200.
...The quality of the naval, war time Leitz 7 x 50 models is good but not 
very good.  The surviving models often have hazed optics, and the Porro 
II prisms are often damaged.  The prism mount obviously did not 
effectively protect the prisms against impact, and in regards to 
temperature changes, was not an effective design.  (Splintering of glass 
at the edges of the prisms can perhaps be caused by different rates of 
expansion between the glass and the prism mount.

4.2.2  Porro II Marine Glasses from other Producers.  France; Huet.
...[page 293] Porro II glasses were released almost simultaneously in 
Great Britain and France, after their development in Germany.  In 1928, 7 
x 50 and 10 x 50 models were produced.  Fig. 44 shows a 10 power glass.  
In these models, a modified Porro II prism system is used (patented by 
Cranz, 1920), see fig. 45 for the image reversal system.
... [page 294]  After the second World War, the 7 x 50 by Huet was 
continued in production, and specimens with coated objectives and the 
usual individual focus are known.  These field glasses were probably 
intended for civilian use.  Similar Huet specimens with rubber coating 
were probably used on French submarines.  Such a glass is described in 
section 4.5 and fig. 264.  Another French marine model with Porro II 
prisms is shown in fig. 237.
...Another interesting Zeiss 7 x 50 model of Porro II design, the U.D.F, 
is described with the U Boat field glasses.

Jena. Zeiss H models   [page 311]
...In 1936 the first German 7 x 50 model with Porro II prisms and 
cemented field lens was built in Jena, the Septar or Septarem.  From 
Zeiss internal records it can be seen that the first series of the 7 x 50 
H, of 300 pieces, was produced in March of 1936.  The Septar has 
individual focus, as do all marine versions of this model, and the center 
focus version was called Septarem.  From the markings it can be concluded 
that these two models were designated for civilian use.  On those glasses 
the specification markings included an 'H'.  (Septar or Septarem 7 x 50 
H; the later military versions were marked D.F. 7 x 50 H.  The H 
indicates an increased brightness - Helligkeit, the field lens of the 
ocular was cemented to the eyepiece to eliminate two glass / air 
surfaces).
...The D.F. 7 x 50 was sold in several versions (fig. 213), most of which 
were probably used by the Navy.   One version had the standard prism 
housing covers as in the civilian version, another had strengthened 
covers and also a special ocular for longer eye relief (for use with gas 
masks).  If present, the reticle was cemented in between the prism and 
the field lens in the Zeiss H models, and therefore protected against 
damage or dirt, and of course also protected against later improvements.
...The Porro II 7 x 50 H from Zeiss included a second version, which was 
built in smaller numbers and used on board ships of the wartime Navy in 
connection with a ‘Richtblinker’ [signal device], see 2.5. During W.W. I, 
the Germans used special high quality and high cost field glasses for 
signal purposes.
...Another variation of the 7 x 50 H can be seen in pictures (see fig. 
214), but more precise data about the exact use is not available.
...All forms of the lightweight 7 x 50 Zeiss Porro II Marineglas are 
noted for their optical quality.  It can be supposed that both models 
were also used in the Army, but the only known wartime photos show use on 
board warships.
...The ‘H’ in 8 x 60 H stands for Helligkeit [brightness], which is a 
result of the optical construction, as in the 7 x 50 H Porro II.   Both 
models have on each side only three optical groups each, and therefore 
have less light loss at the surfaces of the elements.  [page 312]

4.3.  Larger Navy field glasses with Porro I prisms for hand held use.  
4.3.1. Developments from Germany
...[Page 323]  Before 1914 and at the beginning of World War 1, all of 
the leading optical manufacturers included in their programs large bright 
Porro prism field glasses.  The success of the Hensoldt models with 50 mm 
objectives was probably larger than the other optical firms suspected.
...Later military and Navy models were the  'Marine u. Artillerieglas No. 
11' with pentaprisms (1902, see fig. 67), the 'Marineglas' 12 x 50 
(pentaprisms), the 'Spezial-Jagdglas' 10 x 50 (introduced 1904, 
pentaprisms, center focus), and the first 50 mm Dialytes (12 x 50 
'Marine' and 10x50 'Nimrod II' both 1905, available only with center 
focus).  Zeiss followed with a 50 mm objective, the Noctar, circa 1910, 
see fig. 196.  The Hensoldt Pentaprism models and Dialytes, and the 
Noctar, have a roof prism system, which at that time was easier to use 
with a large objective, for optical reasons (see 'Feldstecher', page 
139).  Because of the complicated and therefore expensive roof prisms, 
and surely also because of the patent situation, these prism systems had 
only a limited usage (at the time there were only two manufacturers).
...The Porro I models discussed here have one characteristic in common: 
the distance between the objectives is greater than between the oculars, 
covered by the well known Zeiss patent until 1908.  Most of these marine 
models were built with large objectives (for brightness), and there soon 
developed two different construction forms.  Some of the marine models 
have a lengthened prism housing (for example the 6 x 42), and others have 
a relatively small prism housing, but lengthened objective tubes.( 7x50)
...At the beginning of the first World War, Voigtlaender had already 
produced two models with brass housing & leather coverings, and the 
lengthened objective tubes, a 6 x 42 and a 7 x 50.  Some surviving 
specimens are engraved with the Imperial crown and M, see fig. 219.  The 
popularity of the Voigtlaender 7 x 50 may be explained by the fact that 
Otto Weddigen, legendary U-Boat commander of the U-9, awarded the Pour le 
Merite in the first World War, might have used this glass.*  Busch, 
Rathenow, also made at that time similar 7 x 50 models with Porro I 
prisms.
...The most successful Navy glass was produced in Jena at the beginning 
of the first World War: the D.F. 7 x 50, and the later civilian form with 
individual focus 'Binoctar'.  This field glass was available only with 
individual focus for 15 years after its inception, an indication of its 
intended use in the military and Navy.  Only in 1930/31 was the model 
offered with center focus, as the 'Binoctem', which could be as useful to 
the hunter in the forest and field, as to the naval personnel at sea.
...[page 329]  The 7 x 50 Porro I models were successful and popular, and 
became a classic design, which was followed by many variations and 
special models, not only at Zeiss but world wide.   Daniel Vukobratovich 
from the Optical Sciences Center, University of Arizona, noted in 1993/94 
('Binocular Performance and Design') concerning the need for less than 
fully corrected 7 x 50 models: [page 329, text in English]
...[page 330]  An earlier D.F. 7 x 50 can be seen in fig. 222.  A rich 
history can be read from the engravings: In November 1918, it was in 
service of the German Navy (?), in 1935 it reached Austria and continued 
its service there in the wartime Navy.  The glass was taken to England 
(booty or confiscated after 1945?), to be purchased by a very pleased new 
owner in the 1970s, who purchased it for 15 pounds sterling at a flea 
market.  Why this history?  If the glass were offered in an auction more 
than ten times the price, the provenance of the markings would be highly 
suspicious.  They are easily engraved later, which forgers have 
unfortunately recognized.
...Over the course of time, the 7 x 50 went through the developments seen 
in other service glasses.  The Zeiss models retained the use of aluminum 
(for the body), along with zinc and brass, as the predominant materials 
through W.W.I.  In the thirties, aluminum became more established for all 
metal parts, and the field glasses become lighter.  Leather and hard 
rubber coverings disappeared over time, and the German military and Navy 
models had a black, more or less thick, laquer.  A coarse lacquer was 
used before the first World War (Fernglas 09, see fig. 9, and some 
Hensoldt models).  Leather replaced hard rubber at the end of the first 
World War, because of the shortages of rubber.
...In the time before the second World War, and even more during the war, 
several construction forms or variants of the 7 x 50 were produced.  The 
main danger at sea was the hazing of the optics from the intrusion of 
humidity, and this was countered with a built-in dessicator cartridge.  
Fig.223 shows a freqently seen variant of the Zeiss 7 x 50 Marine model 
where the bottom covers of the prism housing have such a cartridge 
screwed into them.  The ocular of this model has the usual construction 
form.
...[page 333]  Equally common are the 7 x 50 models with 'arrangement for 
use with gas mask', see fig. 224.  The special ocular construction of 
this glass is recognizable by the hard rubber ocular covering, attached 
to sliding rings.  Eye relief is longer in this model.  As mentioned in 
section 2.5, the Zeiss 7 x 50 models with gas mask oculars were also used 
for anti-aircraft defense, and perhaps by the Navy.  Surviving models are 
marked 'M IV/1' and 'T', and with 'Flak.(Kueste)' [coast] or 'Scheinw. u. 
Fluwa.' [searchlights and anti-aircraft arms].  Field glasses of this 
kind might have been used with anti-aircraft search lights, for there are 
pictures from W.W. II showing field glasses which are mounted on a 
horizontal strut next to the searchlight.
...Another Kriegsmarine 7 x 50 from Zeiss, is similar to the usual 
Binoctar, it is a 7 x 50 with neither desiccator cartidges nor gas mask 
oculars.  This relatively rare glass in shown in fig. 225.
...An unusual German 7 x 50 field glass is shown in fig. 226.  It is a 
fixed focus model, the oculars do not have any screw threads for 
focusing.  This characteristic indicates use in a military airplane, but 
the coating indicates use in the Navy.  We can only speculate about the 
exact use, or area of use during the war.  These German military 7 x 50 
fixed focus models are rare, the auther knows of only the two depicted 
examples, both from Zeiss.
...[page334]  Only a few specimens survive of another German 7 x 50 model 
from the Kriegsmarine.  This is a model with eyeguards that can be folded 
to the side, which permits easy cleaning of the eye lenses or use with 
glasses or gas masks.  The model in fig. 227 (top) is furthermore 
distinguished by an ocular lens which sticks above the housing by about a 
millimeter.  These two characteristics can also be found in the U-boat 
glass of fig. 254.
...There were accessories for the Navy 7 x 50s, but only photos survive.  
Frequently these glasses were protected with a rubber covering, which was 
pulled over the housing, see fig. 228.  The rubber was sensitive to sweat 
from the hands, grease and oil, and it soon became sticky, disintegrated  
and lost its durability.  Today no (?) example of this accessory 
survives.
...A field glass is only truly complete with the original case.  The case 
for the 7 x 50 with gas mask oculars can be seen in fig. 224.  This case 
contains further accessories, such as glass filters which can be attached 
on top of the eye pieces.

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