GB560721A - Improvements in or relating to means for determining courses and distances from charts - Google Patents

Abstract

560,721. Optical projection apparatus. BUNSTON, J. E. T. Oct. 13, 1942, No. 14359. [Class 97 (i)] To enable a great-circle guide-screen as described in Specification 414,308 to be used with Mercator charts of differing scales, the screen and chart are combined with means enabling images of each of them to be formed, on the same scale and in superposition, in the eye of an observer; the means may comprise. optical-projection apparatus, or means for ensuring that the screen and chart are at appropriate distances from the observer's eye. As shown in Fig. 1, the screen is carried by a slide in an optical projector 13 mounted under a table 11 having a transparent panel 12 supporting the chart, a screen image being projected on to the chart with the aid of a mirror 29. The projector is'carried by a rack 15 and is adjustable along it to vary the scale of the projected image ; the slide may be moved through a large distance in its carrier 19, by means of a rack and of a pinion rotatable through a flexible connection 23 by a knob 25 at one side of the table. A modification is described in which a projector on a tripod, and a reflector on a standard at a distance from the table 11, produce a beam reflected to the panel 12 by a mirror beneath the table, the standard being adjustable in position to vary the throw and the scale of the projected image. Fig.. 4 shows a chart 51 carried by a wall, a holder 56 for a transparent slide carrying the greatcircle guide-screen, and a ring 54 at which the observer's eye is placed. The slide holder and ring are carried by movable standards 55, 52, connected by a telescopic member 58 so that they may be positioned in accordance with the scales of the chart and screen, and the screen may be moved across the line of sight by a rack-and-pinion mechanism operable by a knob 61 and telescopic spindle 60.