SECTION H       PHYSIOLOGICAL OPTICS AND OPTICAL CONSTANTS

Leitz, Wetzlar and Physiological Institute, Gottingen University

1. Magnification

   Work on the desirable magnification for tank sights had been done by the Waffenampt. Reports on this work had been received by Leitz, but were stated to have been removed by assessors. As far as Leitz could remember, the latest work had indicated that a magnification of X10 might be desirable, but the work was based on a comparison of binoculars and the result appears to have been influenced by conditions in Russia where engagements at 4000 -5000 metres were common. Leitz could remember no details of the trials. The Physiological Institute of Gottingen University stated that a Prof. Ranke had worked on magnification for the Army and it was believed that he was in the Munich area.

2. Exit Pupil

   Here again., Leitz reports had been removed. They stated that the Navy had carried out trials with binoculars and had come to the conclusion that it was not worth while increasing the exit pupil above 6 mm. No details of the work could be remembered.

3. Apparent Field

   Leitz stated that there was a strong demand from the Army for a 70deg apparent field for tank sights. The Army would actually have liked still more, but Leitz felt that the gain was not worth the extra complication in eye-piece design.

4. Binocular V. Monocular Sighting Instruments

   The dropping of the binocular tank sight was not due to any considerations of the relative merits of monocular and binocular vision, but was due to production difficulties when the variable power telescopes with interchangeable erectors were introduced. It was realised that binocular telescopes would show most advantage when contrast rather than angular size was the important factor in visibility.

5. Colour Filters

   The extensive use of didymium glass by the Germans was due to the fact that it improved blue to red contrast. Considerable research was also done on the use of colour filters against camouflage, especially from the point of view of increasing contrast between spectral and composite colours.

6. Form of and Obscuration by Graticule Lines

   No information on this subject was obtained. Work had been done both for the Luftwaffe and for the Army by Prof. Henke.

7. Dark Adaptation

   Extensive researches had been carried out in Germany in an attempt to improve dark adaptation by artificial means. On the whole, the experiments have been unsuccessful,