Binoculars Carl Zeiss Jena Turolem 4x20 (1)

Magnification: 4x
Aperture (objective diameter): 20 mm
Field of view: 10.3°
Exit pupil diameter: 5 mm
Visible field of view (eyepiece FOV): 41°
The closest focusing distance: 2.3 m
Width: 7.5 cm
Height: 10.4 cm
Weight: 300 g
Production date: 1914.

   In 1913 Carl Zeiss produced a small prismatic binocular with a 20 mm objective lens - Turol 4x. The device found application where light weight and small dimensions were required: namely in tourism, sports, theater, etc. A military version of the Turol appeared in 1914 – it was the D.F.4x binocular. It was supposed to be used in light cavalry due to its small size and light weight. However, it didn’t become wide spread, because the cavalry gradually lost its importance for conducting the hostilities during World War I. Therefore, this military binocular became a rarity among the collectors. Both versions (the “civil” and the military one) had the same distance between the lenses and the eyepieces (base), which affected the binocular’s plasticity negatively. It was a rather unusual design solution for Carl Zeiss binoculars of that time, since there even was a condition of Carl Zeiss patent in the period from 1896 to 1908, according to which other manufacturers of prismatic binoculars were required to produce their models with the same distance between the lenses and the eyepieces. This design decision may have been dictated by the desire to reduce the size and weight of these devices.
   The Turolem 4x model with central focusing was launched in 1913 simultaneously with the Turol 4x. Its production continued until 1929, with a break during World War I. Several modifications of this model with various design differences are known for the time being.
   The considered binocular’s specimen belongs to the early modification (produced from 1913/14 up to 1919/20). It has the following peculiarities:
   - rounded objective covers without the grooves to minimize stray light and without the central hinge clamp (lock);
   - the binocular’s marking is made on the central focusing bridge shoulders (later made on the prism covers);
   - the central focusing bridge shoulders are the same thickness (later they had the thickened in the middle part);
   - the focusing scale is located on the focusing flywheel, which is located closer to the binoculars objectives (later - closer to the binoculars eyepieces).
   The binocular’s eyepieces have base diameter equal to 17 mm and the upper prism cover width equal to 38 mm (see photo). The eyepieces’ front lens diameter is equal to 9.5 mm. The eyepieces have a diopter scale and a longitudinal knurling. The binocular’s body height (including the upper prism cover) is equal to 47.3 mm; this value is equal to 39 mm without the lens barrel. The prism covers are pressed to the binocular’s body with the help of lens covers and the “skirts” at the eyepieces’ base. The prism covers are attached on the side to the housing with the help of one screw.
   There are inscriptions “Carl Zeiss Jenna” on the left focusing bridge shoulder. There is also an inscription “Turolem 436141 4x20” on the right bridge shoulder.  The inscription is made in block letters on the background of Carl Zeiss Tessar photo lens schematic image. In addition, the upper disc of the interpupillary distance scale hinge bears the inscription “DIXEY & SON 3 NEW BOND STREET” (see photo). This is a trading partner of Carl Zeiss, the oldest English (London) company, which has been manufacturing and selling various optics for almost 250 (!) Years:      
   The binocular’s serial number is “436141” and it was manufactured as a large 1060 pieces batch in 1914.
   The binocular’s model Turol 4x20 with separate focusing can be checked here.