Small program to calculate the depth of field of a lens, so this is for photographers or people interested in optics theory. It is written in User RPL and the source is rather simple. The source code is commented to help explain things.
This calculates the hyperfocal distance for a lens. When the lens is focused at the hyperfocal distance for a given focal length, eveything from half the hyperfocal distance to the infinite is considered sharp. See source and PDF documentation for details.