Abstract
Photograph is often used in geological survey to measure the length or width of a snapped object, placing some scales such as scale itself, a hammer or a cigarette box nearby the object. However, it is difficult to place a scale nearby the object when the object is too far and high from the taking point or too dangerous to get to the object. In this study, practical applicability of magnification equation of lens for indirect calculation of the length of an object was examined. From this study, following points were made clear (1) Upper limit of applicable distance of magnification equation of lens is more than 300m when the lens whose focal length is longer than 100mm is used. (2) Distortion of a snapped image is within 1.0-2.0%, when the lens whose focal length is longer than 100mm is used. (3) Distortion of a snapped image can be revised using the relationship between the displacement from the correct point and radius from the optical axis. (4) Indirect scale measurement method of a long distant object using a camera and a non-prism razor telemeter is useful. However, accurate measurement of the distance, use of a lens of accurate focal length and accurate measurement of the snapped image on a film are absolutely necessary.
