Magnification

Magnification is the factor by which an object's appearance is enlarged by an optical instrument or image processing. It can be angular, describing how large the object appears to the eye when viewed through the instrument, or linear, describing the ratio of image size to object size on a given plane. Angular magnification is common for eyepieces and viewing devices, while linear magnification is used for photography, projection, and microscopy.

In optics, magnification is produced by lenses or mirrors that bend light. For a thin lens, the linear magnification m is the ratio of the image height to the object height and equals the image distance divided by the object distance (m = v/u). Angular magnification depends on how the instrument channels light to the eye; for telescopes, M ≈ - fo/fe, where fo is the focal length of the objective and fe that of the eyepiece. A magnifying glass provides increased angular size approximately equal to near point distance divided by focal length, often stated as M ≈ 25 cm/f.

Digital magnification refers to enlarging an image by sampling rather than increasing true spatial resolution. While it can make details appear larger, it does not add real detail and often reduces image quality, especially when upscaling low-resolution images.

Limitations include resolution and diffraction. The maximum useful magnification is constrained by wavelength and aperture; beyond a certain point, further magnification only enlarges blur. Instrument design seeks a balance between magnification, resolution, depth of field, and brightness.

Applications span scientific instruments (microscopes, telescopes), photography, eyeglasses, virtual reality displays, and metrology.