Optical Enlargement

The optical enlargement is a Grandeur without dimension which corresponds to the report/ratio of the angle under which is seen the object observed through the instrument optical compared to that under which he is seen with the naked eye.

Contrary to the angular concept of growth, the enlargement does not connect a size of the object to its equivalent for the image, but two sizes referring to two images distinct from the same object. Nevertheless when the object is ad infinitum both concepts of growth and enlargement coincide. Thus the optical enlargement is used to characterize a telescope or the glasses of approach, astronomical or terrestrial or any other subjective instrument whose object is appreciated under an angle only (star, remote object).

The commercial enlargement is a standardized value of the enlargement for which one fixes the distance to which the object with the naked eye to 0,25 m is seen (median value minimum of vision distinct from a healthy eye). It is used to characterize a Oculaire or a Loupe for example.

A contrario, it is not directly used to characterize:

a Microscope, of which one of the characteristics is the optical power (ratio of 2 different physical sizes). Subjective instrument.
a Camera, for which one uses the linear growth (report/ratio of the same physical sizes). Objective instrument .

Article related

Law of Snell-Descartes
Growth (optical)

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