Contact lens zonometer

Apparatus for the measurement of the size of an optic zone of a lens and/or the refractive power of that optic zone, comprising a light source, an illumination system including a first lens train adapted to produce a collimated beam of light from the light source, and a second lens train adapted to focus the collimated beam, mounting means holding the lens being measured and positioned between the first and second lens trains to hold the lens to be measured in the collimated light beam, substantially planar opaque means including an adjustable knife-edged device positioned between said second lens train and an observer and within a part of the focussed beam from said second lens train to occlude said part of the focussed beam, an observation system coaxial with the illumination system, the observation system being adapted to allow the observer to observe the lens to be measured and comprising said second lens train and a further lens which forms an eye piece, said eye piece having an anterior focal plane coincident with the image of the lens to be measured, which image is a single image of said focal plane and is formed by the second lens train, and measurement means including a cross wire fitted to the eye piece at the anterior focal plane and a linear measurement device to measure the translation of the lens to be measured across the mounting means relative to the cross wire to determine the size of the optic zone of the lens.