BINO PRISM Mk4 6E/383 5×40 RAF Spotter Binoculars with Fixed Focus. No.8586

Description

This is a pair of vintage British BINO PRISM Mk 4 6E/383  5×40 RAF spotter binoculars with serial number 8586. These binoculars are in good working order.

Some Main Features:

Model: BINO PRISM Mk4  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: 8586

Dimensions (when binoculars fully open): 180mm (W) x 190mm (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: x5 BINO. PRISM. Mk 4. No.8586

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

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. Lenses and prisms have been cleaned where accessible. (Note: the top prism covers can be opened by loosing the three fixing screws. This can open the cover together with the eyepiece barrel).

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.

General wear and tear appropriate with age and services.

Note: According some information from the web, the manufacture is Ross and the Model is “Bino. Prism Mk4  6E/383 5×40”, with good condition, lens Clear and clean no marks or scratches. 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 gave10%, 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). 

Please see photos for further details.

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