Binocular Carl Zeiss Jena D.F.8x (5)

Magnification: 8x
Aperture (objective diameter): 24 mm
Field of view: 6.3°
Exit pupil diameter: 3 mm
Visible field of view (eyepiece FOV): 50°
The closest focusing distance: 7 m
Width: 15.7 cm
Height: 9.7 cm
Weight: 445 g
Production date: 1916.

   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)
   Earlier, around the end of 1906, first military versions of D.F. 8x binoculars appeared in the new design (an old version is available by the following link - https://binocollection.com/catalog/-binoculars-carl-zeiss-jena-df8x.html). These were the analogs of the “civil” Telact 8x model that appeared a little bit later (https://binocollection.com/catalog/binoculars-carl-zeiss-jena-telact-8x.html). The earliest D.F. 8x devices had their own individual number and they were intended for sale to military people in private order with the permission of military department (for example, the D.F. 6x binocular has the same number - https://binocollection.com/catalog/binoculars-carl-zeiss-jena-df6x-1.html. This model was produced with such marking for a very short time. Later, the serial numbers were shifted to the lower right prism cover edge and they started to put military approval number on the upper right prism cover (under the name of the model).
   The D.F. 8x model in the Telact 8x design was replaced by the D.F. 8x model in the Turact 8x design in 1912-1913: https://binocollection.com/catalog/binoculars-carl-zeiss-jena-turact-8x.html This binocular has a little bit smaller field of view (6.3° versus 6.6°) and slightly worse optical features. However, it is lighter and smaller in size (which is important for military use), as well as more technological (and therefore cheaper) in production. Both models were produced in parallel for some time, so one can find the second type of binoculars with earlier serial numbers in comparison with D.F. 8x/Telact 8x model.
    The D.F. 8x has 8x magnification and 24mm lenses. It’s a military model; similar military models were further marked as D.F.8x24 and D.F.95 n/A.
   The binocular’s “military” application is also proved by the central hinge fixture’s (clamp’s) large diameter and the eyepieces’ protective cover presence (the so called "raincoat" – see photo). The interpupillary distances scale is indicated on the upper hinge disk. The D.F. 8x binocular in the Turact 8x design was produced in 2 versions with various design changes until the mid of 1920s:
   1st version: with the double ring-type lens frames (starting from 1912-13 and up to 1914);
   2nd version: with rounded objective covers in two variations: with grooves on the objective covers to minimize stray light and without them (starting from 1914 and up to the mid of 1920s)
   This device belongs to the second, most popular version, with rounded objective covers and without grooves, intended to minimize stray light. The lens covers are made of zinc alloy. The eyepieces’ base diameter is equal to 20.5 mm and they have the diagonal knurling on the surface (located at an angle 45 degrees). The upper prism cover width is equal to 46 mm (see photo); the binocular’s body height (including the upper prism cover) is equal to 69.5 mm.
   There are inscriptions “Carl Zeiss Jenna” on the left prism cover. There is also an inscription “D.F. 8x 640814” on the right prism cover. The inscription is made in block letters against the background of Carl Zeiss Tessar photo lens schematic image. There is the military acceptance number "177478" on the side surface of the lower right prism cover, and there is also the military acceptance mark "K" - "Gewehr-Prüfungskommission" on the central hinge – it is the marking of the Small Arms Acceptance Board, Spandau (Berlin).
   The binocular’s case has the signs of civilian use, and most likely it does not belong to this device.
   The binocular’s serial number is "640814" and it was manufactured in 1916 as a large 1500 pieces batch.