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equivalent focal length
noun
- optics the ratio of the size of an image of a small distant object near the optical axis to the angular distance of the object in radians
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Example Sentences
The equivalent focal length of a negative or Huygens eyepiece is equal to half the focal length of the larger or field lens.
From Project Gutenberg
When the simple67 expression "focal length" is used, it always refers to the equivalent focal length.
From Project Gutenberg
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