Collecting Military Binoculars
Kern Focalpin 7 - 7 x 50 - 1961
The Swiss-made Kern Focalpin was introduced in 1950 at a Basel trade fair show and was manufactured at least into the 1970’s and possibly until 1988 when the company was taken over by Leica. It was available in three configurations - a 6X40, 7X50 and 10X60. Even though the model was sold for over 20 years, few are found today. The Focalpin has a high build quality and an extremely innovative design and in its time was as expensive as a comparable Zeiss or Leitz product. However, its optical performance was not nearly as good and may have led to low sales and low production numbers accounting for its scarcity.
The Focalpin was meant to be a state-of -the-art weatherproofed, compact and streamlined instrument with large light gathering objective lenses for the outdoorsman and boater. A circa 1970’s advertisement promotes it as having “Maximum proofing against dust, rain and snow...achieved by internal focusing with central adjustment” to be appreciated by “yachtsmen and hunters”. Even though Kern's efforts were successful, this was at the cost of optical performance. The binocular abounds in innovative features. It has a two element air-spaced objective lens to shorten focal length for compactness and to theoretically reduce off-axis aberrations along with a revolutionary third objective lens behind them which slides back and forth for true internal focusing anticipating the construction of today’s roof prism binoculars. It also has very small objective prisms and large ocular ones for compactness, and most unusually one sloping side of each ocular prism is silvered (or possibly aluminized) to provide total internal reflection because, oddly, its reflection surface is not at a 45 degree angle to entrance and exit surfaces as on a normal Porro prism. This was probably done to reduce the height of the prism to save space and streamline the binocular.
As attractive as this innovative binocular is in appearance and as high as it is in build quality, many users find its optical performance disappointing. It has a narrow 5.7 degrees field of view (the 7X50 model has a likewise narrow 6.6 degrees FOV); in spite of its air-spaced objectives the view goes soft about 65% from center which considering its narrow FOV is poor; and the view suffers from a dull grey/green tone. This tone is likely attributable to the nature of the binocular’s anti-reflective coatings, a large number of light reflecting surfaces due to its many lens elements, and the silvering of a prism slope further reducing light transmission and possibly introducing a color bias. Also if, over time, the silvering darkened at all, the view would suffer even more.