[Phys-L] Re: optics terminology

[John Denker <jsd@AV8N.COM>]

Kilmer, Skip requested:
>  a better term for the definition all our testbooks are calling "focal point"?

Two answers:

*) In the special case where that point happens to coincide with the focus,
  I'd just say "at the focal point".

*) In the general case where the focus is somewhere else, I'd might say
  "at a point one f from the mirror" ... but more likely I wouldn't
  say anything at all, because such a point has no particular physical
  significance in this case.  Indeed, for a spherical mirror, there
  are innumerably many points one f from the mirror, none of which
  have much significance except in special cases.  (The _center_
  has significance, but that's something else entirely.)
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