10x80 Flakfernrohr (Flak Glass)

Date: WWII

AFOV: ~74 degrees

TFOV: ~7.4 degrees

Eye Relief: ~16-17mm

Prisms: Schmidt roof prism, 45 degrees

The 10x80 Flakfernrohr or flak glass is probably one of the most recognized German binoculars from World War II.  It was produced in large numbers by several manufacturers.  Emil Busch, Rathenow originated the design around 1935, beating other models in a design competition for the German military.  The other makers of the flak glass included Schneider, Leitz, Goerz, eug (see below), and R. Fuess.  While one of the primary uses for the flak glass was to direct antiaircraft fire, it was also likely used for general observation and  various other purposes.

The optical design of the flak glass uses 45 degree Schmidt prisms and five element Erfle eyepieces with a 2-1-2 configuration.  The focal ratio is rather short at f/3.5, keeping the instrument relatively compact.  See Abb. 145 in Seeger's gray book for diagrams of the optical layout.  The flak glass is basically two telescopes side by side with a knob on the top of the right side to move the left half.   The flak glass is equipped with filters.   The ones I have seen have a knob to select "klar" (clear), "hell" (light), "mittel" (medium), "dunkel" (dark).  Very few had antireflection coatings.

The optical performance of the 10x80 flak glass is very good considering the short focal ratio and lack of coatings.  The field is very wide but it is easy to see the crisp field stop, at least without glasses on.  There isn't quite enough eye relief to see the entire field with glasses.  There is a small amount of the usual field curvature, astigmatism, and pincushion towards the edge but these are not objectionable.  Of course, without coatings, ghost reflections from bright objects are noticeable.

Accessories for the 10x80 flak glass include a rubber padded headrest,  objective shields, aiming sight, illuminator, cradle, tripod, and case.  Very few are found with all the accessories.

For more information on the 10x80 and related models, I highly recommend Stephen Rohan's book "Eyes of the Wehrmacht".

eug 10x80 Flak Glass

Mfr: Optische Prazisionswerke, Warschau (Poland)

Serial Number: 9675 (also stamped 25668 on base)

The eug made flak glass  is uncommon, according to Stephen Rohan.  It is uncoated.

cxn 10x80 Flak Glass (coated)

Mfr: Emil Busch, Rathenow

Serial Number: 77301 36733

The cxn made flak glass is one of the  most commonly encountered.  However, this particular sample is one of the rare ones with anti-reflection coatings.  The coatings have a gold-rose-violet tint and it has been speculated that they are an early multilayer technology, possibly applied during a factory reconditioning.  The coatings appear to be fragile as they show many signs of wear on this sample.

French Hybrid Flak Glass

Mfr: ?

Date: ca 1950?

Serial Number: 80294

This unusual flak glass appears to be a hybrid built for the French Military after WWII from German parts.  One can see on the side the usual German markings but the serial number has been redone.   There are no other markings but the source of this unit said it was French in origin.  The eyepieces are fixed focus but otherwise seem to be similar in performance if not identical to the German design.  My guess is that fixed focus eyepieces, common in French naval optics, were used for water tightness.  The optics are at least partially anti-reflection coated.  The filters are absent.  The other major difference is that the objectives have an aperture of only about 73mm, not 80mm.

In use, this version provides views very similar to the standard flak glass, with essentially the same power and field of view.  One hardly notices the smaller aperture and the coatings are a plus. 

Not present on this unit but seen on other samples of this version is a compass assembly mounted under the right eyepiece, see photo below (thanks to Jean-Laurent Pernice for this photo).