GB796406A - Improvements in or relating to periscopes - Google Patents

Abstract

796,406. Periscopes. BRITISH IRON & STEEL RESEARCH ASSOCIATION. June 27, 1955 [April 8, 1954], No. 10354/54. Class 97(1) A periscope comprises a casing with a number of light transmitting apertures at one end thereof and within the casing an optical system including a reflecting surface designed to cause the entrance pupil of the system to fall near to or externally of the casing, the reflecting surface being movable to align the entrance pupil with any of the apertures to provide the periscope consecutively with different fields of view. As shown in Fig. 1, the periscope has an optical tube 1, inside which is located an optical system comprising, in order from the rear end, an eye piece 2, a central objective 3, a partially light transmitting reflector 4 and a concave mirror 5. In the front of the tube, apertures 6 and 7 are located in the side of the tube 1 and an aperture 8 is located behind the mirror 5. The apertures contain protective windows 12, and register with apertures in a water-jacket 11 surrounding but spaced from the tube 1. Compressed air is supplied to the passage 22 between the water-jacket and the tube 1, and escapes at the apertures 6, 7, 8. Light rays entering one of the apertures 6, 7, 8 fall on the reflector 4. The reflected rays fall on the concave mirror 5 which forms an image I<SP>1</SP>, an inverted image I<SP>2</SP> of which is formed by the objective 3. The image P is viewed by the eye or for photography by a Ramsden eye piece 2. The partial reflector 4 is mounted on a plate 13 pivoted on a shaft 14 and has indexing mechanism whereby it may take up any of three angular positions to select the aperture 6, 7 or 8 to be used. The focal length of the concave mirror 5 and the position of the reflector 4 are so chosen that the entrance pupil, i.e. the image of the central objective 5 formed by the mirror 5 and reflector 4, is located at or outside the optical tube 1. The mirror 5 is apertured to allow passage of light from the aperture 8, which is placed behind it. If desired, a second convex lens 17 may be placed between the reflector 4 and the objective 3 in order to increase the field of view. This lens is slightly tilted to reject a ghost image of the aperture 8 which might otherwise be formed by light reflected from the lens into the concave mirror 5. The aperture of the system is controlled by an iris diaphragm 9 mounted on a slidable inner sleeve 9<SP>1</SP>.