This invention relates to a device for varying focal power along one principal meridian and maintaining a fixed focal plane along the other principal meridian of an optical system. More particularly, the invention relates to such a device having utility in ophthalmic instruments.
U.S. Pat. No. 3,669,530 issued June 13, 1972 to Guyton describes a device for varying cylinder power in an optometer showing arrangements where two cylinder lenses are used in a device to vary the cylinder power. However, the device requires at least two separately moveable segments, i.e. two cylinder lenses or a cylinder lens and a target.
U.S. Pat. No. 3,664,631 issued May 21, 1972 to Guyton describes an optometer having a plurality of cylinder lenses which are slideable along the optical axis. In FIG. 2, believed to be the most pertinent, the center cylinder lens of a three-cylinder lens system is independently moveable within the slideable three-lens system.
The present invention relates to an apparatus which permits variation in the focal power along one principal plane while maintaining a fixed focal plane along the other principal plane. The present invention further permits rotation of the optical assembly for selectively orienting the principal plane having variable focal power.