GB823129A - Improvements in prism lens systems - Google Patents

Abstract

823,129. Optical systems. KODAK Ltd. Aug. 30, 1955 [Aug. 30, 1954], No. 24803/55. Class 97(1) A non-anamorphotic optical system comprises two anamorphotic prismatic systems crossed at right-angles, each system being formed of two refracting prism doublets each rotatable about an axis parallel to its refracting edge, all the prism doublet being rotationally interconnected such that in any position the magnification given by the two prismatic systems is the same and the range of rotational operation giving a magnification from M to 1/M when M is greater than unity. The system shown in plan in Fig. 19 and in elevation in Fig. 20 comprises two compound prisms 191, 192 with their effective refracting edges parallel and arranged on opposite sdes of the optical axis of an objective 57, and two similar compound prisms 193, 194 similarly arranged but with their refracting edges perpendicular to those of the front pair. Thus the prims 191, 192 produce a magnification or reduction in a vertical plane and the prisms 193, 194 a magnification or reduction in a horizontal plane. To vary the magnification each prism is rotatable about an axis parallel to its refracting edge, the pairs of axes being interconnected for simultaneous rotation in opposite directions by gears 231, 232 and 233 and 234 respectively, driven by worms 241, 242 on a rotatable shaft 240. To permit rapid selection of a number of predetermined positions the shaft 240 may slide axially in a bearing 243 being held in the said positions of engagement of a spring- pressed ball with notches 244 in the shaft 240. The system forms an image in plane 58 and to ensure that only collimated light falls on the prisms a lens system consisting of a fixed pane convex lens and a planoconcave lens axially movable for focussing may be provided the two curved surfaces having the same radius of curvature and, when in contact, having their centre of curvature near the entrance pupil of the parts of the system following the lenses. Alternatively rotatoion of the prisms may be effected by a sliding rack engaging the gears 231 and 233, In a modification the prisms may be fixed within a casing the change of magnification being effected by reversing the casing before the objective 57, two such systems being used one behind the other to increase the range of magnification. The prism system may be used to give variable magnification in a telescope, being placed in a position where the light is collimated such as between the lenses of an eyepiece. The system may also be used as a direct vision magnifier the object to be viewed being placed in the plane 58. Specifications 823,130 and 823,131 are referred to.