Another lake

Finally, generalizing the example treated in circular lake let us consider the lake delimited by two arcs of circumference of radii not necessarily equal, and with the same extremes.

In the case of light, this problem corresponds to the study of a lens.

In this example, we are particularly interested in observing several rays starting from a point, crossing the indicated region and, eventually, intersecting after that crossing.

• In the next interactive application, the radius and size of the arcs can be modified, as well as the size of a diaphragm that prevents the passage of very off-centre rays; the observation of the effects of these manipulations allows a better understanding of this rudimentary model of a camera lens.