Mirror in Medium n

Setting the refractive index of the image space to n' = —n for a mirror in medium n, from (1.21) the power is

The focal lengths, conjugate distance equations and magnification are

1 = 1 = 2, 1 +1 = 2, cc = * , M = — z- , (1.26b) f' f R Z z R h h 4 ' z whatever the n index of the medium.

For a mirror in a refractive medium equal to unity, n = 1 = -n', the power is

In the sign convention of the incident light propagating towards z > 0, a concave mirror is with f, f and R all negative and its power K is positive.

With centered systems that are composed of several axially separated diopters, the Gaussian theory provides a powerful method for determining the efl f of the global system. The concept introduces the notion of object and image principal points and principal planes. For a single diopter these planes are both at its vertex. For a global system, the image-side principal plane goes through the intersection point of a ray parallel to the axis in the space object with its conjugate passing through the image focus. Thus, the efl is the distance from the image principal plane to the image focus; this is the rigorous definition of the focal length of an optical system. Its efl calculation uses abscissa transformations of the axial locations of the successive principal planes.

This process provides the paraxial properties of thick lenses and of axially separated surfaces.

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