Binoculars Carl Zeiss Jena D.F.6x (2)

   In 1906-1907, Carl Zeiss radically changed the construction and the design of his binoculars (both “civilian” and military ones). Optical characteristics were significantly improved for the new devices (field of view and the lenses diameter were increased, while optical aberrations were reduced), and the devices’ construction was also changed: the central hinge and the “ears” for the neck strap were not attached to the binocular with the help of screws any more - they became the whole part with it instaed, an eccentric lens alignment system appeared and the design of its frame changed, prism covers spanned the binocular body and they were lubricated with a special compound at the joints with the purpose of tightness improvement. In addition, the prisms inside the binocular were no longer pressed by prismatic covers, but they were fixed with special flat springs, which increased the device reliability significantly.
   The new version of military binocular D.F.6х (its old version is available by the following link: https://binocollection.com/catalog/binoculars-carl-zeiss-jena-df6x.html) appeared a little bit earlier than its “civil twin” – namely Telex binocular - https://binocollection.com/catalog/binocular-carl-zeiss-jena-telex-6x.html, around the end of 1906. This device became the most popular military binocular of the First World War and its release stopped in the 30s of the last century, before the Second World War. Around 1916-1917, the “D.F.6x” label was changed by “D.F.6x24”.
   There are several major modifications of this model:
   1st version: 6x21 - the one, where the lens frame and the lower prismatic cover are made as one component (starting from 1906/1907) and having the eyepieces case with the “transverse” knurling (see photo). Nearly 6,000 specimens were produced with such design option.
   2nd version: 6x21 - the one with double-ring type lens frames (starting from 1908/1909);
   3rd version: 6x24 - the one with double-ring type lens frames (starting from 1911/1912);
   4th version: 6x24 - the one with rounded objective covers (starting from 1913).
   The presented binocular belongs to the 1st version (the lens frame and the lower prismatic cover are made as one component) and it was released as a 100 pieces batch in 1908. The serial number is 145782, there is no additional military acceptance number. The previous, the earliest version of this modification can be checked by the following link: https://binocollection.com/catalog/binoculars-carl-zeiss-jena-df6x-1.html
   The binocular’s “military" application is also proved by the large diameter of the central hinge clamp (lock) (see photo). The interpupillary distances scale is indicated on the upper hinge disk. The eyepieces grooves (knurling) are located perpendicularly to each other (“transverse” knurling), the eyepieces have a diopter scale for acutance adjustment. The upper prismatic cover width is 42.5 mm; the binocular height from lens frames’ lower cut to upper prismatic cover is equal to 65 mm. The eyepieces base diameter is equal to 20.5 mm.
   There are inscriptions “Carl Zeiss Jena” on the left prism cover. There is also an inscription “D.F.6x 145782” on the right prism cover. The inscription is made in block letters (early models had an inscription in italics until 1904) on the background of Carl Zeiss Tessar photo lens schematic image.   Prism covers are made of brass (they were made of such material until 1915-1916, zinc alloy was used later instead) and they are attached to the binocular carcass with the help of three screws.