# tangential plane

A tangential (also called meridional) plane in 3D is in general a plane containing the optical axis.

The tangential plane through a point is the plane in 3D that contains the point and the optical axis.

The tangential ray trough a point in 3D is the ray in the tangential plane through the point, headed to the centre of the entrance pupil.

In the following interactive graphics you can move the green point (click to change directions from x-y to z). The rays leave the point direction entrance pupille and ‘fill’ it completely.

Perpendicular to it is the sagittal plane.

# Tele Lens

Entocentrical lens with a focal lengthlarger than the sensor diagonal, for example a f=8mm lens on a 1/3“ Sensor (that has a 6mm sensor diagonal).
When we use the word “tele lens”, it must be perfectly clear, which sensor is involved.

(Depending on the sensor) the same lens can be wide angle lens, tele lens or normal lens.

# telecentric

With telecentric lenses the image size of an object doesn’t change when the object changes it’s distance from the lens (a little).

a telecentric lens has the same DOF of an entocentric lens (with the same F-number).
Say, the image doesn’t change size when coming closer, but the image starts to blur.

see “comparison entocentric – telecentric – pericentric

# third order optics

does (different from first order optics) include the effects of aberrations on the performance of an optical system.
The image quality is evaluated and the effects of diffraction sometimes included in the analysis.

# total internal reflection

Total internal reflection (“TIR”) occurs, when the angle of incidence of a ray propagating from a higher indes medium to a lower index medium exceeds the critical angle.

[table caption=”Examples for critcal angles” width=”200″ colwidth=”100|100″ colalign=”left|left”]
,
1.3, 50.3°
1.4, 45.6°
1.5, 41.8°
1.6, 37.8°
1.7, 36.0°
1.8,33.7°
1.9, 31.8°
2.0, 30.0°
[/table]

for an interactive example, see refraction