There is a standard piece of terminology which is that the “focal point” is the point lying on the optical axis at a distance from the mirror equal to the focal length. In particular, it is not normal...There is a standard piece of terminology which is that the “focal point” is the point lying on the optical axis at a distance from the mirror equal to the focal length. In particular, it is not normally the place where the rays come to a focus! --- that would be the image point. That is, it appears to be what grammarians call a “skunked term” --- a word that bothers half the population when it's used incorrectly, and the other half when it's used correctly.
