Re: [ATM] Additional phase contrast and Foucault images

["Stephen Koehler" <s.c.koehler@gmail.com>]

Dominic,

> In a sense we are opposites; I have not done simulations, but I
> do have practical hands on experience with phase contrast
> imaging (about 20 years).

I have gravitated toward simulations as a learning tool, because of
lack of time to pursue real mirror making and testing, at the moment.
Simulations can be a great learning tool, but are no substitute for
real experience.

> Since I am in the coming weekend or
> two needing to set up my Foucault tester, maybe even more valuable
> than those nice pics (Stephen) just provided would be a pic or two
> of the actual rig from the poster (Dale?) that showed that pic
> with the multiple mirror images, and I can see what I can do with
> it? Not sure I'll have a comparable parabola (after all, I had a
> reason for setting up my tester, like checking a surface I'm working).

The second mirror in Dale's post my 18" f/4.5.  It is coated.  Here's
what I know about Dale's setup.  Perhaps Dale can fill in any gaps.
The light source is from a slide projector with a slit in front of the
lens.  I don't know what slit widths he used, but I understand he got
the best results with a pretty narrow slit.  The phase plate was
constructed from a 3x3 square of glass with a 5 to 10 mm wide soot
line deposited on it by a candle.  One side of the line was cleaned up
by scraping the glass with a sharpened wooden stick (like a dull
chisel).  Only the cleaned edge was used.  Images were taken near the
COC of the 70% zone.  I don't know the transmission of the soot line.
I looked through it, yesterday, and I estimated it to be somewhere
between .1 and .25 transmission.

-- 
Steve Koehler
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