[ATM] Phase contrast and the 10 incher.

[Dale Eason]

You are making sense.  I thought you were asking about
the phase contrast images and not the Foucault image
since the subject references phase contrast.

I do know that Foucault can see stuff on the back
surface and front surface combined.  I have seen that
case and it was clear where each feature was comming
from.  

I'm still not certain where the worm tracks are
located but am leaning towards inside.  Only because I
believe they are the veins that Texereau talks about.
However an argument against that is what you say and
that they have smooth floors.  If they were below the
surface then we should also see lap caused ripple over
top of them and we do not.  

I have done the phase contrast camera lens foucus
experiment and the features stay but just get a little
blurry.  It takes a defocus of more the 3 feet from
them to get only a tiny bit blurry.

Moving the knife is a different thing and that only
changes the very lower order SA terms that change the
surface from a bowl, torus, and hill.  The worm
features remain throught that movement.

Dale Eason

--- Arjan te Marvelde <arjan.te.marvelde at hetnet.nl>
wrote:

> Dale, Dominic-Luc,
> 
> Maybe I don't understand how the foucault test
> works, but as far as I know,
> the intensity of the returned light is to a large
> extent related to
> measuring in the image of the lightsource, as it is
> created by the mirror
> surface shape. What you normally see as structures
> on the surface (usually
> larger scale) are deviations from the surface shape.
> Light that is reflected by just any randomly shaped
> sub-surface structure
> just scatter the light, and hence will be
> overwhelmed by the in focus image
> itself.
> If this were not the case, the visibility of the
> structures must be
> independent of foucault focus! This is an easy test
> to do: just move the KE
> a few inches in or out, or don't use a KE at all...
> 
> So assuming this statement holds, the only
> structures that will become
> visible in foucault focus would have to be related
> to the surface, being
> either on the surface, in the surface or in an other
> way follow the shape of
> the surface.
> 
> Am I making sense?
> 
>    Arjan
> 
> > I carefully focus on the front surface using a
> target
> > placed on the mirror.  When not focued on the
> surface
> > then features that I am sure are on the surface
> are
> > slightly blurred.  All features show regardless of
> > focus.
> >
> > Perhaps focus is a way to figure out the dept of
> them.
> >  What I recall however is that the finger prints
> are
> > usually sharp.  I will have to check that.  I know
> the
> > finger prints are only on the back surface. I
> don't
> > believe they are etched into the front surface
> > although I know it can happen.
> 
> 


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