Binoculars Carl Zeiss Jena Marineglas 6x (4)

?Magnification: 6x
Aperture (objective  diameter): 30 mm
Field of view: 8.4° 
Exit pupil diameter: 5 mm
Visible  field  of view (eyepiece FOV): 50° 
The closest focusing distance: 7 m
Width: 16.7 cm
Height: 11.5 cm
Weight: 635 g
Production date: 1909.

   In 1907, Carl Zeiss radically changed the framework and the design of his binoculars, replacing "civilian" models Feldstecher 6 Fach by Telex, Feldstecher 8 Fach by Telact, Jagdglas by Silvamar and Feldstecher 12 Fach by Telefort. The new devices’ detailed characteristics were published in the 74-th volume of Carl Zeiss catalog in August 1907. The optical characteristics were significantly improved in new devices (the field of view and the objective  diameter were increased, optical aberrations were decreased), and the devices’ design was also changed: the central hinge and the “lugs” for a neck strap were not attached to binocular with the help of screws any more, they became integral with it instead, an eccentric objective alignment system appeared and its frame design was also changed, the prism covers spanned the binoculars’ carcass, and they were lubricated with a special compound at the joint points in order to improve impermeability. Moreover, the prisms inside the binoculars were no longer pressed by prism covers – they were fixed with the help of special flat springs instead. It helped increasing the device’s reliability greatly. Actually, the binoculars have survived in such appearance up to present days (see Hans T.Seeger. Zeiss-Feldstecher, Handfernglaser von 1894-1919, Modelle-Merkmale-Mythos, pp.399-414)
   The Marineglas is a military analogue of a "civilian" model Silvamar with similar characteristics. It is the first binocular model with 30mm lenses. The device turned out to be very successful, with high aperture ratio, plasticity and large field of view, that is why it became popular in the army. Although the name of this device is translated as the "sea glass", it was not widely used in the German Navy: only some batches entered the fleet. The Marineglas was produced from 1907/08 and up to 1917 with various modifications. Later the binocular name was changed to D.F.6x30.
   The Marineglas was produced in several design versions starting from 1907/08 and up to 1917:
1st version: the one, where the lower prismatic cover and the lens frame cap are made as one component (starting from 1907/1908 and up to 1909) and having the eyepieces case with the “transverse” knurling.
   2nd version: the one with long double-ring type lens frames, leather-covered and with a short case (starting from 1909/10 and up to 1911);
   3rd version: the one with short double-ring type lens frames (starting from 1911 and up to 1913/14);
   4th version: the one with rounded objective covers (starting from 1913/14 and up to 1917 in two versions: with the grooves to minimize stray light and without them).
   This rare binocular has a short body design with long “double-ring” type lens frames, which were produced for a short time from 1909 to 1910/11 (see above). The eyepieces’ base diameter is equal to 24.5 mm, the eyepieces’ front lens diameter is equal to 14 mm. The eyepieces have a diopter scale and the transverse knurling. The upper prism covers are made of brass and are fixed to the body with the help of three screws. The prism covers’ width is equal to 52 mm (see photo). The binocular’s body height (including the upper prism cover) is equal to 55 mm. The binocular’s “military" application is proved by the large diameter of the central hinge clamp (lock) (see photo). The interpupillary distances scale is indicated on the upper hinge disk.
   There are inscriptions “Carl Zeiss Jenna” on the left prism cover. There is also an inscription “Marineglas 162607 6x” on the right prism cover. The inscription is made in block letters with the help of silver alloy on the background of Carl Zeiss Tessar photo lens schematic image.
   The binoculars have the serial number “162607” and were manufactured in 1909 in a batch of 450 pieces. Interestingly, in the well-known book by Hans T. Seeger. Zeiss-Feldstecher, Handfernglaser von 1894-1919, Modelle-Merkmale-Mythos on page 805 this batch of binoculars with serial numbers in the range 162251-162700 is marked as an unknown (?) model.
   The binocular "civilian" analogs, the Silvamar 6x models, can be checked by the following link.