GB784144A - Improvements relating to the counting, size ascertainment, density measurement or other examination of objects - Google Patents

Abstract

784,144. Photo-electric apparatus for examining objects. CASELLA (ELECTRONICS), Ltd. Oct. 21, 1955 [Oct. 21, 1954], No. 30302/54. Class 40 (3). Apparatus for examining objects such as microscope slides and photographic plates or films comprises a mask 1, having an aperture such as a slit 2 illuminated by means of a steady light source 3, means for scanning the image of the aperture over the object 11 and registering or recording means 19 indicating the light transmitted by the object as determined by photocell 18. The scanning means comprises a rectangular (or other multisided) prism 5 rotated so as to cause the image of the slit to move across a section of the object. The repeated vertical scans across the object caused by rotation of the prism 5 may be combined with movement of the object at rightangles to the direction of scan so that the whole area of the object is investigated. As shown, a sharp reduced image of the mask aperture is obtained by introducing an inverse microscope 8 between the prism 5 and the image plane. This also reduces the linear scanning movement due to rotation of the prism and to prevent the reduction the inverse microscope may be placed before the prism (Fig. 5, not shown). Alternatively the image produced by the inverse microscope may be formed in the plane of a second apertured mask and an optical magnifying system used to produce an image in the plane of the object (Fig. 3, not shown). In a modification of the apparatus two dimensional scanning of a fixed object is achieved by the use of two refractive prisms 5a and 5b rotating about axes at right-angles to each other. The apparatus may be used for particle counting, size determination, and density or colour measurement. Specification 714,350 is referred to.