Page 70 - Modern Optical Engineering The Design of Optical Systems

Chapter
4

Optical System Considerations

4.1 Systems of Separated Components
An optical element is a single irreducible optical lens or mirror.
An optical component may be an element, or several elements which
are treated as a unit.
An optical member is one of two parts of a system, separated by a
diaphragm: the front member and the back member.
An optical system is a complete set of optics which produces an
image of the desired size, in the desired location, and with the desired
orientation.
In order to simplify and organize the design of optical systems, it is
convenient (especially in preliminary work) to treat an optical system
as an arrangement of components, each with zero thickness. In pre-
liminary work we can deal with components as simple, unified pieces.
A component may consist of several elements, but in creating a system
layout scheme, we simply specify the power (or focal length) of a com-
ponent and its location. When the initial layout is done, the zero thick-
ness components are replaced by real, physically possible components.
This avoids having to handle the system by means of surface-by-surface
calculation. To this end we can introduce the paraxial ray height y into
the equations of Sec. 2.3, just as we did in Sec. 3.3.
An optical component (which may be made up of a number of elements)
is shown in Fig. 4.1 with its object a distance s from the first principal
plane and its image a distance s′ from the second principal plane. The
principal planes are planes of unit magnification, in that the incident
and emergent ray paths appear to strike (and emerge from) the same
height on both the first and second principal planes. Thus, in Fig. 4.1

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