Binoculars Carl Zeiss Jena D.F.8x (2)

Magnification: 8x
Aperture (objective diameter): 24 mm
Field of view: 6.6°
Exit pupil diameter: 3 mm
Visible field of view (eyepiece FOV): 52.8°
The closest focusing distance: 5.8 m
Width: 14.8 cm
Height: 12 cm
Weight: 570 g
Production date: 1913.

   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).
   In 1912-1913, the D.F. 8x binocular in the Telact 8x design was replaced by lighter and smaller (which was very important for military use) model D.F. 8x in the Turact 8x    https://binocollection.com/catalog/binoculars-carl-zeiss-jena-turact-8x.html. For some time both models were produced in parallel, so you can find the second type of binoculars with an earlier serial number compared to D.F. 8x/Telact 8x.
    The D.F. 8x model is a tall binocular with very good optical performance, 8x magnification and 24mm lens. 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 (see photo). The interpupillary distances scale is indicated on the upper hinge disk. The D.F. 8x binocular in the Telact 8x design was produced in 3 versions with various design changes until 1916:
   1st version: the lens frame and the lower prismatic cover are made as one component (starting from 1906) and having the eyepieces case with the “transverse” knurling.
   2nd version: the one with double-ring type lens frames (starting from 1908 and up to 1913) https://binocollection.com/catalog/binoculars-carl-zeiss-jena-df8x-1.html;
   3rd version: the one with rounded objective covers in two variants: with grooves on the objective covers to minimize stray light and without them (starting from 1913)  
   This device belongs to the third, rare version with grooves on the objective covers, intended to minimize stray light, and it has the eyepieces with base diameter equal to 24.5 mm and the top prism cover width equal to 50 mm (see photo). The eyepieces possess a diopter scale and the diagonal knurling (located at an angle 45 degrees). The binocular’s body height (including the upper prism cover) is equal to 80 mm.
   There are inscriptions "Carl Zeiss Jenna" on the left prism cover. There is also an inscription - “D.F. 8x 359126" 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 binocular’s serial number is "359126" and it was manufactured in 1913 as a 400 pieces batch.