Re: ATM horror story

[Stephen Tonkin <sft@aegis1.demon.co.uk>]

Glen,

If I understand you correctly, you have a 6" mirror and are finding the
*Centre of Curvature* 9 feet from the mirror. This will equate to the
focal length being 4' 6" -- f/9.

Just let's check -- are you 9' from the mirror when the flashlight,
which is also 9' from the mirror, suddenly fills the mirror? If so, that
is CoC, not FL -- you are pretty close to where you want to be, so don't
regrind.

You are not the first and won't be the last to muck up a perfectly good
mirror through a little miscalculation. I recently made a moving-source
tester and treated my results as though they were from my fixed-source
one. When my mistake dawned on me, I (foolishly) went back over all my
test data, only to find that I had gone through a very good paraboloid
the previous week...

Glen Bankston <microsys@alltel.net> wrote:
>i kept playing with it tonight, not getting what i was expecting.  so in
>an experiment, i put the mirror way far away and shined a flashlight in
>it.  all of a sudden the imaged magnified greatly, and showed a fairly
>well defined focus 9 feet away.  Boo hoo!  what a dummy!!



--
Stephen Tonkin