- 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.
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 ofoptical imaging systems and the direction where no birefringence occurs in optically birefringent non cubic crystals.
- Optical Density
Optical Density (OD) is the logarithm, base 10, of the ratio of the incident light to the transmitted light:
where Io is the incident intensity and I is the transmitted intensity. If neutral density filters are placed in series, the optical density of the combination is the sum the individual density values.
- Optical Glass
Optical Glasses are transparent, usually amorphous, and essentially homogeneous materials whose manufacturing processes are controlled in such a way as to create a desired variation in glass material characteristics such as Refractive Index, Transmission Range, Dispersion, etc.
- Optical Path Lenght (OPL)
The OPL of a light ray passing through a medium of constant Refractive Index, is the product of the geometrical distance d and the index of refraction n:
- Principale Plane
In a lens system, that surface at which the projections of an entering and exiting ray intersect.
In optics, Reflection is the return of radiation upon contact with a boundary between two different media.
There are two types of Reflection:
Diffuse Reflection from a rough surface
Direct Reflection from a smooth surface.
The characteristics of Reflection at the boundary of a weakly or non-absorbing media are summarized by Fresnel's equation.
- Relay Lens
An optical system able to transfer an image plane to another with appropriate Magnification.
- Resolving Power
Is the measure of the ability of an optical component or instrument to image two closely adjacent object details as two separate details.
In general Resolving Power is given as the angular distance at which these details appear or as the number of resolvable lines per mm.
- Telecentric System
Is an optical system where the aperture stop is located at the focal point of the objective lens resulting in the chief rays being parallel to the optical axis, i.e. the exit pupils at infinity.
- Total Internal Reflection
f light is incident on a boundary between two optical media of different optical densities and is incident from the denser medium, it will experience Total Internal Reflection.
The critical angle for the two materials is described by Snell's law:
where n' is the index of the denser medium.
Is the passage without frequency change of radiation through an optical medium.
Vignetting is a mechanical limitation of oblique light rays passing through an optical system.
Vignetting cannot be caused by the aperture stop.
- Visible Light
It is radiation which as the capacity to generate visual sensation.
Spectral Range of Visible Light lies between 380nm and 780nm.
- Working Distance
It is the distance between the first lens and the object plane.
- Zoom Lens
It is an optical system of variable Focal Lenght, with the Focal Plane remained in a fixed position, while some of the elements move along the lens axis.