[Phys-L] Re: optics terminology

[SSHS KPHOX <kphox@CHERRYCREEKSCHOOLS.ORG>]

Forum for Physics Educators <PHYS-L@list1.ucc.nau.edu> on Tuesday,
February 7, 2006 at 12:41 PM -0700 wrote:
> When I first responded to John's question, I was not in my office and
> didn't have a supply of textbooks to examine.  Now that I'm in my
> office, I find the same thing John said.  Every book I examined says the
> focal point is the place where paraxial rays come to a focus.  That
> makes the focal length always equal to the distance between the lens and
> the focal point, just like John said he read.

Not an expert, but when I started teaching in 1966, using the PSSC text,
the point of convergnce of the parallel rays was called "principal focus".
I have always liked that term and still use it my self.

Ken Fox
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