Binoculars Carl Zeiss Jena D.F.8x (6) Trentact design

Magnification: 8x
Aperture (objective diameter): 30 mm
Field of view: 6.0°
Exit pupil diameter: 3.75 mm
The closest focusing distance: 6.5 m
Width: 17 cm
Height: 10.3 cm
Weight: 645 g
Production date: 1912.

   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 binocular which we are considering is the pride of any optical instruments’ collection. For the time being, there are no more than 4-5 such devices in private collections. It doesn’t belong to any of Carl Zeiss Jenna catalogues, and there are no mentions of it in the official documents of that time either. The D.F.8x is the first Carl Zeiss Jenna military binocular with an aperture (objective diameter) equal to 30 mm and 8x magnification. The D.F.8x has its own civilian “brother”, not less rare than itself, namely Carl Zeiss Jenna Trentact 8x. There is also a civilian version of this binocular with a unique side focusing – it is Carl Zeiss Jenna Trentactem 8x (a rare binocular with an identical focusing type - ).
   The binoculars with 8x magnification and 30 mm lenses’ diameter produced by other manufacturers were quite in demand among both civilians and military people before the outbreak of World War I. Why did this model never become as mega-popular as, for example, the wide-angle (with Erfle eyepieces) Carl Zeiss Deltrentis 8x30 (D.F.8x30)? Perhaps the reason should be sought in the following: even before the outbreak of World War I, the Carl Zeiss company employee, a famous German optician Heinrich Erfle, developed a popular wide-angle eyepiece that acutely increased the binoculars’ visible field of view. Perhaps, the Carl Zeiss management decided that new binoculars with Erfle eyepieces would be simply out of competition compared to the D.F.8x with “ordinary” eyepieces, which we are considering now (the first wide-angle binocular with Erfle eyepieces appeared in 1917) and they simply stopped producing the latter one.
    So far, we know about two modifications of the D.F.8x binoculars:
   - the one with double-ring type lens frames;
   - the one with rounded objective covers
   This early version of the device belongs to the first group of binoculars, namely with double-ring type lens frames. The upper and lower prism covers are made of brass and they are fixed to the carcass with the help of three screws. The prism covers’ width is equal to 51.5 mm (see photo). The binocular’s body height (including the upper prism cover) is equal to 77.5 mm.The eyepieces’ base diameter is equal to 24.5 mm, and the eyepieces’ anterior lens diameter is equal to 11.5 mm. The eyepieces also have a diopter scale and the diagonal knurling (at 45 degrees angle).
   The binocular’s “military" application is proved by the large diameter of the central hinge clamp (lock) and the goniometric grid in the right eyepiece presence (see photo). The interpupillary distances scale is indicated on the upper hinge disk.
   There are inscriptions “Carl Zeiss Jena” on the left prism cover. There is also an inscription “D.F.8x 309703” 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 “309703” and it was manufactured in 1912. According to Hans T.Seeger book Zeiss-Feldstecher, Handfernglaser von 1894-1919, Modelle-Merkmale-Mythos, p.817) this number belongs to a Turact 8x 200 pieces batch (numbers 309701-309900). Perhaps, a small part of binoculars from the beginning of this batch still belonged to the D.F.8x model.
   The binocular’s coffer has military features peculiar to that period (see Hans T.Seeger. Zeiss Handfernlaser 1919-1946, Modelle-Merkmale-Mythos, pp. 607-627): the top cover attachment to the coffer carcass, specific rivets, a wide loop for coffer attachment to the waist belt. The top cover is made using seamless technology. There is a poorly readable inscription “Hptm. ???? PA6” on the coffer top cover: probably the binocular belonged to a soldier - hauptmann (hauptmann - Hptm. – is a junior officer rank in the German imperial army).