The
decrease in illumination away from the optical axis in an
optical system caused by clipping of off-axis rays by apertures
in the system.
Virtual
Image
A
virtual image does not represent an actual convergence of
light rays. A virtual image can be viewed only by looking
back through the optical system, such as in the case of a
magnifying glass.
Visible
Radiation (light)
Electromagnetic
radiation which can be detected by the human eye. It is commonly
used to describe wavelengths which lie in the range between
400 nm and 700-780 nm. The peak of the human spectral response
is about 555 nm.
Visible
Spectrum
The
region of the electromagnetic spectrum ranging from 400 nm
to approximately 700 nm.
