Re: Insomnia = brilliance?

[Brian Reynolds <reynolds@xxxxxxxxx>]

Bob wrote:
> 
> >   I'm thinking of just removing the taking
> > lens/shutter from all the cameras and
> > using them as a projection lens. Use them
> > to project some corner dots, mark them
> > on the wall and try the next lens. We'll
> > have to discuss this more later.
> > 
> >   Ideally we could have a standard method
> > then Bob and I can each measure our lenses
> > and then do some swapping if necessary to
> > get the best match.
> > 
> Yes, that would be great--I was thinking along the same
> lines, but don't have any concrete ideas yet.  Maybe we
> could build a crude, shipable optical bench set-up with
> a projection bulb, condensor lens, slide-holder, and a
> place to mount a camera with the back taken off?
> 

Sam Brown's "All about Telescopes" (from Edmund Scientific) has a
section on building an optical bench and collimator.  You can measure
the focal length of a lens either by measuring the images size of a
test target (basically the projection method that Greg mentioned), or
by auto-collimation.  Unfortunately auto-collimation requires a good
(i.e., flat) first surface mirror.  The bench and collimator are
pretty easy to make (the collimator needs a good achromat, 3 inch
diameter with a 24 inch focal length is mentioned as being good for
testing 6 inch diameter telescopes), and if you make a postscript or
PCL file of the test target available on the web you wouldn't need to
ship anything.

-- 
Brian Reynolds                  | "Humans explore the Universe with five
reynolds@xxxxxxxxx              |   senses and call the adventure science."
http://www.panix.com/~reynolds/ | - Edwin P. Hubble