Re: [ATM] Foucault imaging fast mirrors?

[aart@insightbb.com]

Use a microscope
objective to reimage the foucault image plane.  The knife edge is
placed at the standard spacing behind
the objective lens (160 or 170mm are common), where the eyepiece would be
(although you
don't use an eyepiece) and your eye or camera is
behind that.  The mirror sees the knife edge imaged at the object
end of the lens, where the microscope slide would be.  The lens has to
have a
numerical aperture able to capture your mirror's f/3.1 light
cone.  It's a bit of trouble to set up, but in
addition to making the spacing comfortable, this also decreases
(by the magnification of the lens, e.g. 10X) the off-axis measurement astigmatism caused by lateral separation of
light source and
knife edge, so it's a good thing for fast mirrors generally.

Aart Olsen

----- Original Message -----
From: Dominic-Luc Webb <dlwebb@canit.se>
Date: Wednesday, May 2, 2007 4:08
Subject: [ATM] Foucault imaging fast mirrors?
To: ATM Superheros <atm@atmlist.net>

> 
> I set up my Foucault rig (classic/generic razor blade 
> construct). Test
> subject is a 310 mm diameter F/1.55 partially polished plate glass
> sphere (slumped). I thought this was going to be quick and easy, but
> I encountered a couple of difficulties. First, light source had 
> to be
> changed because it was only illuminating part of the mirror, and when
> that was fixed I realized my rather small Canon A-85 CCD camera
> cannot get close enough to capture the fully illuminated surface with
> the light source within 5 cm of COC: lens hits razor blade before
> getting close enough to obtain a fully illuminated surface.
> 
> Anyone have experience with actually getting CCD image of Foucault
> pattern for such fast system? Is this worthwhile test?
> 
> Dominic
> 
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