10x80 80 Degree Flak Glass

Date: WWII

AFOV: ~70 degrees

TFOV: ~7 degrees

Eye Relief: ~22mm

Prisms: Amici roof prism, 80 degrees

The 10x80 flak glass with eyepieces inclined at 80 degrees was used by the German Kriegsmarine primarily for antiaircraft spotting.  It was introduced circa 1938 and manufactured by Zeiss and Optische Prazisionswerke (eug).  The 80 degree incline facilitated pointing it at steep angles into the sky, compared to the standard 45 degree flak glass.  Other differences with the standard flak glass are the integrated cradle and mount, and antireflection coatings as a standard.  The focal ratio appears to be longer than that of the standard flak glass, which likely helps the optical performance.

Originally the 10x80 80 degree model came in case with accessories including filters, batteries and illuminators for the reticle and aiming circles.  The binocular mounts onto a standard German military optics tripod.  Early versions had a simple aiming tube while later versions included a blc (Zeiss) optical aiming device.  The blc aiming device (also found on other instruments) presents a roof or pyramidal shaped pattern, which can be set for day ("T") or night ("N") use by rotating the front section.  The day setting uses natural light illumination for the aiming pattern while the night setting uses internal illumination (believed to be from a radium type paint).

The optical performance of the 10x80 80 degree is outstanding, noticeably better than the 45 degree flak glass.  The field of view is essentially the same but there is better eye relief with the 80 degree model, enough to see the entire field with glasses on.  The edge of field correction is quite good, helped by the long focal ratio.  The antireflection coatings also help to improve performance.  According to Kevin Kuhne the eyepieces are six element Erfle types.  The oversized Amici type prisms put the roof lines well off the center of the field, so they do not affect the image as much.  The 80 degree 10x80 binocular is a real pleasure to view through.

eug 10x80 Flak Glass

Mfr: Optische Prazisionswerke, Warschau (Poland)

Serial Number: 62034

This particular sample of the 10x80 80 degree binocular was made by eug.  Note the "T" on the cradle, indicating coated optics.  The handle on the left sets the altitude, while the handle on the right locks in the azimuth.  There is also a knob on the right to set the interpupillary distance.  This model has the blc aiming sight on the right side tube, attached to a dovetail mount.  Originally the eyepieces had rubber eyecups, missing on this example.