From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


The shearing interferometer as described in Peter John Smith's webpage,
should show about 2 to 10 fringes on the half mirror segment visible.  If
you move the plate closer and adjust the angle, you see fewer fringes. 
More than 10 leaves no visual ability to see how straight they are.

Is you eye close enough to get full illumination?  Just as in the Foucault,
your eye must accept the full width of the returning beam.

http://www.users.bigpond.com/pjifl/page15.html

Colin

-----Original Message-----
From: Jean-Guy Moreau [mailto:jgmoreau{at}cablevision.qc.ca]
Sent: Monday, February 17, 2003 5:29 PM To: CSC
Subject: Re: ATM Tesing a spheriod?


hi Colin,

i built one also, seems to work as it should but i can only see 4 bands in the
center
of the spherical 10" mirror i use for the test. I use a slit source.
what am i doing wrong ?

thanks for suggestions,

jean-guy
in Quebec


-+-
> I do not use a slit for the shearing interferometer.  I find the size of
the
> diode is small enough for this test, and also small enough for an
artificial
> star test.  At 700X, it is still a point in the eyepiece, with beautiful
> textbook refractor type diffraction rings.
>
> I think the plate over the diode will not make a difference.  This test
> takes the entire returning beam and splits and folds it on itself.  It is
> the same wavewfront until it hits the shearing plate.  Known as a Common
> Path Interferometer.
>
>
> The glass plate that does the wavefront reversal (shear) must be almost
> exactly on the axis at the COC/focus of the rays.  It is in the same place
> that a knife edge would be, and it may help to actually laterally cut the
> returning beam with the glass plate as if Foucault testing, then back it
> just out of the path.  Then twist it to get the shear. If you are too far
> off the axis, it won't recombine the wavefront at the extremely small
angle
> required to get fringes.
>
> Setting the block that holds the glass plate on a strip of stiff paper,
like
> from a file folder, makes it easy to adjust the angle.  Simply use the
paper
> strip as a handle to rotate the block assembly.
>
>
> It's touchy at first.  Then it's real easy ever after.

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