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Field of View:
The field of view is the outer most point of the field angle capable of
being transmitted through a lens system to form an image. A field stop, an
aperture stop, or images in either object or image space can induce this
spatial limitation.
Focal Length:
Focal length is
defined as the distance between the principal plane and the corresponding
focal point for parallel rays. Focal length is a function of lens radii,
glass type and thickness and is the most important characteristic of any
optical imaging system.
Index of Refraction:
The index
of refraction is the ratio of the velocity of light in a vacuum to the
velocity of light in an optical material at a certain wavelength:
N=Cv/Cm
Magnification:
Magnification is the radio of
image size to object size measured normal to the optical axis: m’=y’/y.
Modulation Transfer Function
(MTF):
MTF is a quantitative
description of the image forming power of an imaging system. To measure MTF,
increasingly fine lines of known contrast are imaged by the optical system
and the image modulation is measured in the image plane. The ratio of the
image modulation to the object modulation for different line resolution and
separation (spatial frequency) yields the modulation factor. The MTF is a
plot of this factor versus spatial frequency. Most MTF’s are calculated.
Numerical
Aperture:
Numerical aperture is defined as the sin of the half angle of
the widest ray-bundle capable of entering a lens, multiplied by the index of
refraction of the medium through which the ray-bundle passes. NA=nxSin u.
The term numerical aperture has special significance for microscope lenses.
Objective
Lens:
An optical system able to focus an image at infinity.
Optical
Axis:
In optics, the term optical
axis has two meanings: The symmetrical axis of optical imaging systems
and the direction where no birefringence occurs in optically birefringent
non-cubic crystals. |
