Unity Vision Block with Focal Plane

The vision block is essentially a window 8 in. wide, 2 in. high and 4 in. thick. Because of refraction, this gives a very wide almost 90 deg horizontal field of view, with a wide aperture which permits binocular vision over much of the field. It is impossible to achieve all these features with an intermediate focal plane within the space limitations. The design problem then is to make an optimum tradeoff among field of view, aperture and image quality, consistent with conforming to the 4 inch vision block dimensions and intended use. A unity-magnification telescope with an intermediate focal plane has been designed to fit into the outer housing of a standard No. 6300790 tank vision block. This has a 29 deg field of view with an exit pupil of 16 mm, at an eye relief of 70 mm. A slide permits insertion of test cells in the intermediate focal plane for evaluating laser protection devices. The intensity of an incident laser beam is increased by a factor of 50,000 at the intermediate focal plane. Two units have been built and tested. They show no degradation of normal vision over the entire focal plane.