PURPOSE: Demonstrate on-axis astigmatism.

DESCRIPTION: On-axis astigmatism is the type which occurs in the eye. Light from a bright point source is focused onto a pinhole, which acts as the object for the system. The pinhole object is then focused by an "astigmatic lens" consisting of a 10 cm focal length spherical convex lens and a 30 cm focal length cylindrical convex lens. The vertical focus is a horizontal line and the horizontal focus is a vertical line; between these two foci is the "best" focus circle of confusion. The foci are shown by moving a ground glass screen along the optic axis.


REFERENCES: (PIRA 6A65.34) Also see Demonstration L6-37: ASTIGMATISM, which demonstrates off-axis astigmatism from a lens, and Demonstration L6-36: STRING MODEL - ASTIGMATISM.

EQUIPMENT: Bright point source with 10cm lens, pinhole, 10cm focal length spherical convex lens and 30cm focal length cylindrical convex lens, with ground glass screen, on portable optical rail cart.

SETUP TIME: 5 min.

Go back to Lecture-Demonstration Home Page.