GB402516A - Improvements in or relating to sight-testing apparatus - Google Patents

Abstract

402,516. Sight-testing apparatus. PULZER, L. S., STEARMAN, S. R., 45, Hatton Garden, London, and MAXWELL, E. H., 472, London Road, Croydon. July 4, 1932, No. 18911. [Class 97 (i).] In apparatus of the kind in which two lens holders, one carrying a set of positive lenses and the other a set of negative lenses, are so mounted on a frame that the positive and negative lenses can be placed in succession independently of one another into the field of vision by adjusting the holders, the negative lens holder is arranged to carry as many or substantially as many lenses as the positive lens holder carries. The apparatus comprises two similar casings, one for each eye, each containing a set of positive and a set of negative lenses, and each having an aperture in the field of vision. As shown, the negative lens carrier comprises two discs 15, 16 mounted co-axially on a plate 19 which is connected by spacing members to the main frame plate 18 having an aperture 20 in the field of vision. Each disc 15, 16 has six apertures which can be brought successively by rotation of the disc into register with the aperture 20, five of these apertures carrying negative lenses and the sixth being blank. The disc 16 is freely mounted on the hub 33 of the disc 15 which is provided with a toothed rim gearing with an idle pinion 47 which can be rotated by a toothed wheel 48 secured to a spindle 49 having an actuating knob 50. Secured to the disc 15 is a wheel 52 having a single tooth 53 which engages once in each revolution of the disc 15 with a star wheel 55 fast with a toothed wheel 57 meshing with a toothed wheel 58 secured to the disc 16 so that the disc 16 turns through one-sixth of a revolution for each revolution of the disc 15 ; thus all the lenses in the disc 15 can be brought in turn into register with each lens of the disc 16 and with the aperture 20. The lenses in the disc 15 may have powers of -À25, -À5, -À75,- 1, and - 1À25 D, while those in the disc 16 may be - 1À5, - 3, - 4À5, - 6, and - 7À5 so that all powers from -À25 to -8À75 D by steps of -À25 can be obtained. An auxiliary lens of - 9 D may be pivoted to the casing so that it can be brought into the field of vision when required to enable powers from - 9 D to - 17À75 D to be obtained. The power of the lens or lenses in the field of vision is indicated by graduated discs 62, 61, the disc 62 being secured to the spindle 49 and of such diameter that it turns through 90‹ for each step of the disc 15. This disc bears the graduations 0, À25, À50, and À75 while the disc 61 bears the whole numbers from 0 to 8 and is intermittently rotated by the disc 62 by gearing similar to that described above so as to turn through one ninth of a revolution for each revolution of the disc 62. The disc 61 has gaps through which the numbers on the disc 62 can be read and both sets of numbers are observed through a window 63.