BINO PRISM MkIV 6E/383 5×40 RAF WWII Spotter Binoculars with Fixed Focus. No. 2980

Description

This is a pair of vintage British BINO PRISM MkIV 6E/383  5×40 RAF WWII spotter binoculars with serial number 2980. These binoculars are in good working order.

Some Main Features:

Model: BINO PRISM MkIV 6E/383 5×40 spotter binoculars

Magnification: 5 x

Objective lens diameter: 40mm

Eye lens diameter: 17mm

Fixed focus (i.e., no need to adjust image focus while using the binoculars, an important feature for aircraft spotting, see note below).

Serial number: 2980

Dimensions (when binoculars fully open): 180mm (W) x 185mm (H) x 65mm (D)

Solid metal body construction with admiralty style thick layer of black paint protection.

Net weight: approx. 1.05 kg

Engraved on top left prism plate: BINO. PRISM. Mk IV. No.2980

Engraved on top right prism plate: 6E/383 B

Marked with the Ministry of Defence broad arrow

General wear and tear appropriate with age and services.

Comes with original leather neck strap.

Please see photos for further details.

Note: The binoculars are in good working condition with correct collimation and reasonably nice images for their fixed focus design feature and age. No damage to the optics. Eye lenses and prisms under the eyepiece cover have been cleaned where accessible. (N.B.: the top prism cover can be opened by loosening the three fixing screws. This can open the cover together with the eyepiece barrel).

When looking into the binoculars through objective lenses, there appears to be some small dusts on the lenses which have not been opened for cleaning. However, these are not visible while looking through the binoculars in normal way and it does not seem to affect the image and performance of the binoculars in any way.

For further technical information, while these fixed focus spotter binoculars allow their users such as aircraft pilots to quickly find targets in different distances, their image clarity is not as high as the binoculars with fine focus adjustment. This is a design feature of those fixed focus spotters in the old days.

According to some information from the web, the manufacture is Ross and the Model is “Bino. Prism Mk IV  6E/383 5×40”. The “B” marking on right prism cover indicates the optics are “bloomed”, i.e. coated, and the marking “6E/383” is a Royal Air Force stores code for this type of instrument. This is a fixed focus aircraft spotting and maritime reconnaissance including U-boat spotting binocular. It is reported but not confirmed that it was used by observers in Beaufighters and other nightfighters during WWII. The Mk.IV was built by Ross under Royal Air Force contract, introduced in 1941, and continued to be used at least into the 1960’s. It was succeeded by the 5×40 6E/392. It is the first British war-time binocular to employ coated lenses. According to a 1943 report by the Admiralty Research Laboratory, the x5 Mk. IV’s 8 mm exit pupil gave 10%, 15% and 25% “improvements” (in light transmission) under respectively half-moonlight, starlight and dark conditions compared to a 7X50 Admiralty Pattern 1900 (probably a Barr & Stroud CF41). 

More information on How to identify or estimate the production dates of vintage binoculars.