Stigmatic points

Any point on the diopter is the image of itself, this image conjugate is of course stigmatic.

Any luminous ray arising from the curvature center C is perpendicular to the diopter and is not deviated. Therefore C is the image of itself and the image conjugate is stigmatic.

There is another diopter stigmatic conjugate for which the relationship (7) is rigorously verified. These points which are situated on the same side as the diopter rigorously satisfy the relationship : n'.IA' = n.IA

The optical path (AA'), is rigorously nil, this shows stigmatism. Figure 14 is an example of this conjugate image type (n = 1,8 et n'= 1). These particular points are Young-Weierstrass' points, they are often used in microscopy.

For these points :