Patent GB-291771-A (GB)
Title: Improvements in or relating to photographic apparatus
IPC: G03B17/02
Filed: 1928-06-08
Abstract: 291,771. Sequin, A. June 8, 1927, [Convention date]. Void [Published under Sect. 91 of the Acts]. Cameras, baseboard fittings for.-A focusing- device is provided on the camera, whereby the objective may be adjusted to focus sharply objects lying within a desired range, and the device when set indicates automatically the diaphragm aperture which must be used in the object to ensure the necessary sharpness of focus. In the form shown in plan in Fig. 1, the objective panel 3 is drawn forward, from its housed position, along guides on the slide 2 until it is arrested in the infinity position by a stop 6. The folding baseboard 1 has slideways 16 along which the slide 2 may be racked forwards by turning the knob 11 in order to focus near objects. Between the slide 2 and the baseboard 1 are mounted two parallel plates 20, 21 rigidly connected together and adapted to turn on a pin 13 fixed to the baseboard 1. The plate 20 carries a pointer 8 moving over a focusing-scale 10 on the baseboard, and the plate 21 is slotted at 25 to receive a pin 12 fixed to the slide 2, so that when this is racked forwards from the infinity position shown in full lines in Fig. 1, the plates 20, 21 are rotated, and the pointer 8 moves over the scale 10, until the slot 25 reaches the position shown in dotted lines in Fig. 1 and the pointer 8 is arrested simultaneously at the end of the scale 10. Further forward movement of the slide 2 causes the pin 12 to slide along and out of the slot 25 without rotating the plates 20, 21. Mounted loosely on the shaft 13 are two elbow levers 7a, 9<a> carrying pointers 7, 9 working over the scale 10 on each side of the pointer S, and equidistantly therefrom. These pointers are caused to move simultaneously towards or away from the pointer 8 by moving a pointer 36 over a scale of diaphragm apertures 37 engraved on the plate 21. The pointer 36 is carried by a lever 33 turning on a pin 35 journaled in the plates 20, 21, and carrying an eccentric 32 resting in an aperture 31 in a sliding plate 27 guided parallel to the line y-y of Fig. 2 as by racks and pinions 28, and slotted at 30 to permit it to move relatively to the pin 13. Pins 40 fixed to the plates 20, 21 in symmetrical positions with regard to the line y-y of Fig. 2, engage slots 38 in the tails of the levers 7<a>, 9<a>. Rotation of the lever 33 thus turns the eccentric 32, which displaces the slide 27, and this in turn, through the pins 40 and slots 38, rotates the levers 7<a>, 9<a> through opposite equal angles. In order to set the objective, from its infinity position, so that it will sharply focus all objects included betweean two specified distances from it, the slide 2 is racked out until the pointer 8 lies midway between the readings on the scale 10 which correspond to the two specified distances, and the pointer 36 is then moved over the scale of diaphragm apertures 37 until the pointers 7, 9 rest at the aforesaid readings on the scale 10. The pointer 36 then indicates the diaphragm aperture to be used in order to obtain the degree ot sharpness for which the scales 10, 37 are calculated. The optical considerations underlying the construction of these scales are discussed mathematically in the Specification.