[ATM] Phase contrast and the 10 incher.

[Dale Eason]

Dominic-Luc,
Perhaps you missed the following

http://home.comcast.net/~doeason/bvmirror/bvmirror.pdf

as you can see from that posting the mirror is not
coated.

The mirror is 1.75 inches thick.


Now to reply to other issues by multiple posters.

I'm no expert on the theory but here is what I know.
Humans only see intensity of light and not its phase. 
Phase contrast changes the phase into intensity that
we can see.  It does that with light reflected from
the object.  The object changes the phase of light
through both reflection and transmition.  So light
that is reflected by the back passes through the glass
twice and if the path is a little different the phase
is altered by both the back and the interior.
Irregularities in the glass can change its phase
without changing its intensity. That is how features
on the back, interior, and front can all be seen in
one image.

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. 

What I call the worm tracks have broad smooth floors
and steep sides, usually are curved and many have a
serpentine shape.  Whether they have steep rising
sides or deep valleys at the side of them depends on
how your brain sees them.  You can turn the image
upside down and they usually reverse.  Texereau has
images of them on page 62 of the second edition.  He
does not identify them exactly in his description. 
Instead he says the image shows micro ripple from
polishing and veins in the glass.  What I think are
veins in his images are more or less parallel to one
another.

This mirror does have veins in the glass that are
easily visible from the side.

My images also have the ripples so I believe them to
be on the surface.  I don't know for sure if the worm
tracks are part of the ripples or veins. 

Many of the worm tracks have large heads and thin
tapering tails.  These look like pouring features so
that is why I believe them to be veins in the glass.

The worm tracks could be the last broad strokes of a
few lap faces.  The ripples could then be the last
vestiges of the worm tracks having been crossed by the
lap many times.  If so then they too are on the
surface and are not veins in the glass.  At present I
don't believe the lap works as I just described. 


Dale Eason

--- Dominic-Luc Webb <dlwebb at canit.se> wrote:

> 
> 
> Oh yeah, one more point, don't mark the front (with
> anything
> like ink). Mark the back.
> 
> Yet another reason to think this is not actually on
> the
> back, is that apparently this is a mirror that has
> already been coated, so I do not think we will see
> the
> back. Marking the back side with thick blank ink
> should
> settle this. However, coating seems to involve both
> aluminizing and a protective coating, and this could
> explain a few things, maybe even the multiple images
> we
> discussed earlier. Perhaps this is inside the
> coating?
> 
> Dominic
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com