GB1140352A - Improvements in or relating to focimeters - Google Patents

Abstract

1,140,352. Focimeters. HANWELL OPTICAL CO. Ltd. Feb.22, 1966 [Jan. 21, 1965], No.2691/65. Heading G2J. A focimeter comprising a graticule D, an optical system for projecting an image of the graticule on to a screen C and means for supporting a spectacle lens under test between the graticule and the screen, is provided between the lens support and the screen C with an optical correcting element L which is movable transversely of the optical axis to ensure that the graticule image is centred on the screen C. The spectacle lens is supported at the free end of an objective tube A<SP>2</SP> which is mounted in a wall of the focimeter housing A. Light passing from a source B through the graticule D, the objective F, and the lens under test is directed by a mirror K outside the focimeter housing towards an aperture therein which is closed by a low powered negative lens element L. This lens element is releasably clamped to the housing wall and is adjustable in a plane at right angles to the optical axis. When the lens under test is in position, the graticule D, is moved along the optical axis until a sharp image appears on the screen C, the distance moved being a direct measure of the power of the lens. The distance may be indicated by a scale E6 fixed to the graticule D, an image of which scale is projected by a further optical system on to a screen C' so as to register with a pointer marked on the screen C'. The graticule D may comprise an opaque disc bearing a plurality of double rows of transparent dots arranged radially of the disc. In order to find the axis of astigmatism in the lens under test the graticule is rotated until the dots of the graticule image merge into lines. Means may be provided for marking the horizontal axis of the lens under test during the test.