Abstract: A test pattern is displayed on a planar display surface 14. The power of a test lens 20 is determined by measuring the magnification of the test pattern as seen through the test lens with the test lens at two different lens distances dl1, dl2 from the display surface and calculating the power from the two magnification values and the difference in lens distance ?dl. Apparatus for carrying out the method includes a digital display screen 14 for displaying the test pattern and a digital camera 16 for capturing images of the test pattern through a test lens 20. The apparatus has a lens carriage 18 in which a test lens 20 is mounted to hold the test lens between the display screen and the camera. The lens carriage 18 is movable under control of an electronic control system 28 in a linear direction perpendicular to the display screen to vary the distance between the test lens and the display screen.

Abstract: A test pattern (170) comprising a set of dots (174) which define a first ellipse (176) of best fit in which the major and minor axes R1, R2 are equal (i.e. a circle) is displayed on a plane surface and a digital image of the (usually distorted) test pattern seen through a lens is captured. A second ellipse of best fit joining the dots in the set is derived from the distorted test pattern in the image. Characteristics of the first and second ellipses are compared to determine the degree and nature of distortion to the test pattern, from which the power of the lens is calculated. The major and minor axes of the first and second ellipses may be compared. The test pattern can include a number of said sets of dots distributed over an area of the surface with each set being analysed to determine the optical parameters of the lens at multiple locations.

Abstract: A system (101) for examining lenses in a pair of glasses includes a tablet computer (112), a camera (128) mounted above the computer screen and a glasses mount (156) for holding a lens in a pair of glasses between the camera and the display screen. The camera (128) is operatively connected to the computer for storing and processing image data captured by the camera. In use, a test pattern is displayed on the screen below the camera and an image of the test pattern seen through a lens is captured by the camera. Image data is saved to the computer which processes the data to determine the power of the lens from the distortion to the test pattern caused by the lens. The results are displayed on another section of display screen. The camera mount (156) may be a plinth slidably positioned on the display screen.

Abstract: A test pattern (170) comprising a set of dots (174) which define a first ellipse (176) of best fit in which the major and minor axes R1, R2 are equal (i.e. a circle) is displayed on a plane surface and a digital image of the (usually distorted) test pattern seen through a lens is captured. A second ellipse of best fit joining the dots in the set is derived from the distorted test pattern in the image. Characteristics of the first and second ellipses are compared to determine the degree and nature of distortion to the test pattern, from which the power of the lens is calculated. The major and minor axes of the first and second ellipses may be compared. The test pattern can include a number of said sets of dots distributed over an area of the surface with each set being analysed to determine the optical parameters of the lens at multiple locations.