demagnification

Demagnification refers to a reduction in the linear size of an image relative to its object. It is the opposite of magnification and is defined by the linear magnification m = hi/ho, where hi is the image height and ho the object height. Demagnification occurs when |m| < 1. If m is negative, the image is inverted relative to the object.

In optical systems, demagnification is common when the goal is to fit large objects into a smaller image plane or to transfer patterns to a smaller medium. Examples include projection optics in photolithography, where the reticle patterns are reduced to create smaller features on a silicon wafer; typical demagnification factors range from 2x to 5x and higher in modern deep ultraviolet steppers. Demagnification also occurs in camera and sensor systems that capture a scene with a finite sensor size; many relay or imaging lenses produce a smaller image on the sensor than the object size.

Demagnification is not limited to industrial contexts; it can occur in general imaging where the image plane is closer to the lens than the object or where a sequence of optical elements reduces the image size. The effect is sometimes designed into an instrument to control field of view, fit images to a particular detector, or manage resolution and sampling. Overall, demagnification describes any situation in which the image produced by an optical system is smaller than the object being imaged.

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