Re: [ATM] RE: Foucault Simulation analysis of non-symmetricaberrations

[Bernard Maugoust <maugoust@free.fr>]

In message <200410021725.AA2628255914@mail.johnspics.com>, 
 "john sherman" <atm@mail.johnspics.com> wrote:
 
> Hi Bernard, 
> 
> >the recipe for making the tiny *round* hole.
> 
> I learned that trick right here, on the atm list. I'm sorry I don't
> remember who posted it - as I recall, a few people have given the same
> recipe.

I did search, probably with the wrong choice of keyword. I might try again.
 
> Take a nice needle and look at the tip with a loupe (or 25mm eyepiece). It
> will probably not look very sharp. Sharpen it up with very fine sandpaper
> or a hone. Take a stack of aluminum foil pieces. I usually cut a bunch of
> pieces from a beer can and stack them up. Put your stack on a very hard
> thing, like a steel slab. Poke the needle into the stack of foils, give it
> a light tap with a small hammer if need be. It is best if the needle
> doesn't poke all the way thru to the bottom layer. 
> 
> Now examine the holes created and you will find a variety of different
> sizes. Take care to illuminate the hole evenly. I use very fine sandpaper
> to roughen up a green led.

Lovely. A quick trial already brought better results than my yesterday's
attempts with food wrapping foil ;-) Cutting the light path with a hair
unmistakingly shows the 'Phi' picture. Many thanks for the tip John.

I'll refine my hole-making technique now and get a brighter LED. I'm
currenttly using a blue one (3mm diam.) rated at 470 nm and 570 Mcd, and find
it pretty dim compared to what I see using the traditional knife-edge method.
I'd go for a green (520 nm) at 5600 Mcd.

As for the spot, I'm yet trying to get hold of microscope slides, which
proves less easy than anticipated :-(

> If you have any more questions, please ask.

Thanks. If I produce good enough pictures while testing, I'll upload them
onto my list page.

Right now the only one (knife edge) is here:

http://www.atmlist.net/contrib/maugoust-at-free-dot-fr/Foucault%20Pics/fouc2.jpg

Regards,

-- 
Bernard Maugoust 3°59'E 44°28'N

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