GB410518A - Improvements in projection screens - Google Patents

Abstract

410,518. Projection screens. ZAFIROPULO, J., 51, Rue de Passy, Paris. Nov. 18, 1932, No. 25375/33. Divided on 410,515. [Class 97 (i).] A screen for the projection in relief of pictures obtained in the manner described in Specifications 410,515 and 410,517 is made of a number of lens elements having an aperture ratio of at least f /4 and preferably f /2.5. The screen can be used with an objective A, Fig. 1, the effective aperture of which is increased by means of reflectors S, Z, so as to bear the above ratio to its distance from the screen Q, i.e. a /b = 2.5. The foci of the lens elements of the screen Q are in the rear surface of the screen. To avoid the necessity for increasing the diameter of the objective A, a filter consisting of three colour bands i, k, l, Fig. 3, may be placed in front of the objective and corresponding colour strips J<1>, K<1>, L<1> applied to the rear surface of each element of the screen. This surface is turned towards the projector and the pictures are seen by transmitted light. The screen shown in Fig. 4 has convex front elements g, and concave rear elements h, the curvatures being so related, having regard to the thickness of the screen, that parallel rays incident on the front refracting surface are, after refraction thereat incident normally on the rear surface to which a layer c of silver &c. is applied. This screen may be homogeneous as shown, or it may consist of two layers of acetyl cellulose &c. in which the lens elements are formed and an intermediate layer of glass to which the lenticular layers are cemented.