Magnification

Lore & Background

Magnification is quantified by optical magnification, a dimensionless ratio of apparent size to true size. For real images projected on a screen, linear or transverse magnification is used, measured in linear dimensions. For virtual images seen through an eyepiece, angular magnification is defined as the ratio of the tangent of the angle subtended by the image to that of the object, often approximated by the angle ratio for small angles. For example, the Moon's angular size of about 0.52° appears as about 5.2° through 10× binoculars.

Reader's Guide

Magnification is a fundamental concept in optics, enabling the detailed observation of small or distant subjects. It is applied in instruments such as magnifying glasses, telescopes, microscopes, slide projectors, and zoom lenses. The magnification of a thin lens is given by formulas involving focal length and object distance, with sign conventions indicating image orientation (negative for inverted, positive for upright). Angular magnification is standard for magnifying glasses and microscopes, using the near point of 25 cm as a reference. Understanding magnification is crucial for designing optical systems and interpreting visual data, as it does not alter perspective but only apparent size.

Did You Know?

• Optical magnification is sometimes referred to as 'power', e.g., '10× power', though this can be confused with optical power.
• For a thin lens, linear magnification M = -di/do = hi/ho, where negative M indicates an inverted image.
• The mean angular size of the Moon's disk as viewed from Earth's surface is about 0.52°; through 10× binoculars it appears to subtend about 5.2°.
• Longitudinal magnification ML is defined along the optical axis direction, using the Newtonian lens equation f² = x0 xi.