longitudinal magnification
Quick Summary
In optics, longitudinal magnification refers to the factor by which an image increases in size when measured along the optical axis. This is distinct from linear magnification, which measures the ratio of image length to object length perpendicular to the optical axis.1
If an object moves a short distance along the axis, the corresponding image shift is related by the longitudinal magnification, denoted as m. This relationship is expressed as:
[ m = m^2 ]
where m is the lateral magnification. This indicates that the longitudinal magnification is always positive, meaning the image moves in the same direction as the object. A large lateral magnification results in an even larger longitudinal magnification, explaining the very small depth of field in microscopes. Conversely, a small lateral magnification, as seen in cameras, results in a small longitudinal magnification, allowing a wide range of distances to appear in focus.2
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