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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.

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.

sin(\theta_{c}) = \frac{n_2}{n_1}

[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°
1.9, 31.8°
2.0, 30.0°

for an interactive example, see refraction