equivalent focal length

noun

1. 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

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