2.9 Summary of Important Points
1. Lenses and other optical imaging systems can, in most cases, be treated
as two-dimensional, shift-invariant, linear systems.
2. The assumptions involved in the use of linear analysis of optical systems
begin to break down as one moves far off the optical axis, particularly
for wide-aperture, low-magnification systems.
3. Under coherent illumination, an optical system is linear in complex
amplitude.
4. Under incoherent illumination, an optical system is linear in intensity
(amplitude squared).
5. An optical system having no aberrations is called diffraction-limited
because its resolution is limited only by the wave nature of light
(diffraction effects). This is an ideal situation that real systems can
only approach.
6.