[Phys-L] Ray Diagrams

[cvbritton at EARTHLINK.NET (Chuck Britton)]

Please, when 'doing' ray diagrams, include MORE rays than the
requisite 'principal' rays.
The principal rays are only 'special' because we can do the geometry
with them easily.
I think that it is important to emphasize that ALL rays that share
the same origin as the principal rays do - will end up at the same
point as do all of the principle rays.
It's awful easy to JUST do the principle rays - and this sometimes
makes these rays seem overly 'special' or somehow the 'only' rays
that behave in this manner.

> I have found ray diagrams less then obvious to students unless
> you spend some time working with them in a simple context.  I use
> McDermott's...no relation??...material on projecting light through
> holes to do this.  We take ray diagrams as simple and straight (pardon
> the pun) forward.  My experience is that they are not to the
> uninitiated.