| 摘要 |
PROBLEM TO BE SOLVED: To provide a focal distance measuring method capable of measuring the focal distance of a lens simply and precisely. SOLUTION: In this focal distance measuring method, the light emitted from a light source 2 is condensed by a microlens array 3, the light expanded again after being condensed is condensed by a measuring lens 4, it passes through a neutral density(ND) filter 5, and an image is formed on a light detector 6. The microlens array 3 or the measuring lens 4 is moved to obtain the relative distance between the microlens array 3 and the measuring lens 4 when the received light quantity of the light detector 6 becomes the maximum and the relative distance between the microlens 3 and the measuring lens 4 when the received light quantity of the light detector 6 becomes the minimum, and the focal distance of the microlens array 3 is obtained from the difference between both relative distances.
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