GB1142064A - Optical focusing arrangements - Google Patents

Abstract

1,142,064. Automatic lens focusing. BELL & HOWELL CO. 24 Oct., 1966 [24 Oct., 1965; 30 Aug., 1966], No. 47587/66. Heading H4D. [Also in Division G2] The Specification describes automatic lens focusing means, especially useful in camera apparatus. The main lens 27, which is to be focused on a film &c. 29, is slaved to an imaging lens 11, by means of co-operating racks 37, 33 and worm gear 41. Light from the object to be focused is nominally focused on to a lenticular screen 13, which is moved across the optical path, such that, due to the passage of the lens elements of the screen through the beam, a photo-cell 15 will receive pulses of light from the beam, unless the lens 11 is exactly focused on the screen 13, corresponding to the focusing of lens 27. The screen 13 may be rotated by a motor 19 in which case the screen may be circular as in Fig. 2, having radial lens elements 52 extending over all the disc or only over part thereof (Fig. 3, not shown). The phase of the alternating current which energizes motor 19 is compared with the phase of the output of the photo-cell in phase discriminator 23 and the resultant signal used to energize a servomotor 25 driving worm gears 41. The screen may comprise parallel cylindrical lenses 57, Fig. 5, and be oscillated in a direction perpendicular to the lenses by a solenoid 63, Fig. 4. If the lens 11 is spring biased to be normally at one end of its movement (Fig. 7, not shown), the phase discriminator may be dispensed with, and the amplified and integrated output of the photo-cell used directly to energize the worm drive motor. If the lens 52 or 57 focal length is greater than a predetermined value, the output of the photo-cell will give shallow nulls for other than the focused condition. To overcome this, lenses of different size are used (Figs. 8, 9, not shown), together with integration of the photo-cell output as in Fig. 7. The screen may comprise three radial cylindrical lenses (Fig. 12, not shown) co-operating with a cam which operates a switch when a lens crosses the beam. Operation of a switch opens a gate at the photocell output, thus reducing the effect of noise which may occur in the photo-cell output between said beam crossing times. The gated output of the photo-cell goes negative or positive, depending on whether the focal point of lens 11 is in front of or behind the lenticular screen. A negative or a positive bi-stable circuit is accordingly triggered, to provide the driving power for motor 25.