Patent GB-551157-A (GB)
Title: Improvements in profile projectors
IPC: G02B21/00
Filed: 1941-06-03
Abstract: 551,157. Optical gauging-apparatus. SMITH, Ltd., C. F and SMITH, C. F. June 3, 1941, Nos. 7037 and 14222. [Class 106 (ii)] [Also in Group XX] In optical-projection apparatus for gauging objects, the test object and one or more standard objects are each illuminated by a substantially parallel beam from a separate light source, comparison images are formed by objectives each associated with one object, the front foci of the objectives are arranged in close proximity, and reflecting means is arranged at or near the foci to produce a nearly common light beam and to enable substantially the whole area of each objective to be utilized ; images formed by the objectives at infinity may be projected on to a screen by one of alternative imaging lenses of different powers, variation of throw being effected by variation of mirrors between the imaging lenses and the screen, or may be viewed by means of a telescope system. Fig. 16 shows an optical system in which light sources 8, 82, and condeners 10, 16, produce parallel beams received by objectives 11, 17 having nearly coincident front foci, a prism 18 being located at the front focus of the objective 17 to direct the beam therefrom into substantial coincidence with the beam from the objective 11. The objects 83, 84 may be placed at the back foci of the objectives, thus producing images at infinity which are both imaged on a screen 4 by one imaging lens 20 at its focal length from the screen. One or more additional light sources, objects, objectives, &c., may be provided, with additional reflectors at the front foci, and an additional lens forming, at the back focus of each condenser, an image of each light source of unit magnification may be provided in each lighting system. Figs. 2 and 4 show in elevations at right angles, apparatus wherein a light source 8, unit magnification lens 9, and condenser 10, illuminate a test object mounted between centres 7, and an objective 11 has a roof prism 13 at its front focus. A standard held between centres 53 is illuminated by a similar lighting system having a horizontal optical axis, and an objective 17 has an isosceles reflecting prism 18 at its front focus, the prisms 13, 18 being juxtaposed. Two imaging lenses, respectively having focal lengths 25 and 50 times that of the objectives, are carried by a plate 19 rotatable by a knob 22 to bring either lens before the prisms. The lens of shorter focal length, in conjunction with reflectors 25, 26 and 27, produces images on a screen 4 beneath a hood 5 ; their images may be brought into coincidence by plane-parallel plates 23, 24, respectively rotatable about vertical and horizontal axes by means associated with graduations providing measures of the adjustments. When the other imaging lens is used, the reflectors 25, 26 are swung out of position, and the beam is reflected by mirrors 31, 32 and 27 to the screen. The centres 7 are carried by crossed slides 37, 71, respectively adjustable by micrometer heads 36, 73 by means described in detail. The centres 53 are adjustable vertically and horizontally by means described in detail, and may be replaced by a graticule bearing a representation of a screw thread form &c. or by a protractor. The lighting system for the centres 7 may be swung between cheeks 80 to tilt the axis of the light beam in accordance with the helix angle of a screw held by the centres. A telescope system comprising a reflecting prism, and a Romsden eyepiece is described for use instead of the imaging lenses reflectors and screen.