Lensometer, Automatic, Testing
Monday, September 11, 2006
An Automatic Lensometer is an optical bench consisting of an illuminated moveable target, a fixed field lens, and a telescope eyepiece focused at infinity. The fixed field lens is located with its focal point at the back surface of the lens being analyzed. The small movement of the target is amplified optically. The distance between the target and the field lens is always proportional to the power of the unknown lens. This particular setup allows the Lensometer linear scale to be read in diopters.
To determine the power of an unknown lens, insert the lens into the lensometer, locate the principal meridian ray, focus the target lines and record the power of the lens. Refocus a second target, which is rotated 90 degrees from the first target, and record the power of the lens again. Using both recorded powers of the two principal medians and the axes, the actual prescription can be calculated.
The Lensometer can rapidly measures lens powers for any meridian ray. It then selects the median rays with the greatest differences in power between them. This designates the major meridian rays of the lens. The lensometer computer processes the information, calculating the prescription..
Source: Various Publications
References: None Available
Industrial Products
posted by JD52 @ 7:33 PM,
1 Comments:
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At 3:38 PM,
Tom said...
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To actually see how the lensometer reading is performed, you might find the video at this site useful:
lensometer video
It goes through each of the focusing steps.
