Re: [ATM] First Timer Polishing Questions

[Mark Holm <mdholm@telerama.com>]

Meeks Robert-PT1784 wrote:
> Thanks to all for your input.  A couple of follow-ups below:
> 
> <Bob May Wrote>
> "The thing that you have to remember is that the glass surface
> will reflect about 4% of the light from the pointer."
> 
> Hi Bob - I've read your past posts regarding the 4% but I have been
> confused on this point.  I don't know if this will come across, but let
> me try a little text "drawing" to illustrate my question.  
> 
>  A   B   C      D
>   \     /
>    \   /
>     \ /
>  ---------------
>       \
>        \
>         E
> 
> If the laser is at point A, and the mirror surface is the horizontal
> line, then some amount of light passes through to point E and some
> amount of light is reflected up to point C.  Are you saying that on a
> perfectly polished surface, 96% of the light passes through to point E
> and 4% is reflected to point C?  If yes, then I would expect to see NO
> reflection at points B or D.  If no, then you are indicating that points
> C and E together represent 96% of the light, and 4% of light is
> scattered around, such as to points B and D.  In that case, I would
> always expect to see some small disk on the surface of mirror.
> 
> What's confusing is that the Stellafane site indicates pretty adamently
> that you will see no scatter of light at points B or D, but I've tried
> this test on eyeglass lenses and my wife's crystal wine glasses when she
> wasn't looking and I always see a little red dot on the surface of glass
> from different positions, even though most of the light either passes
> through or is reflected at the appropriate angle.  Hence, my confusion.
> Thanks for you time to help clear this up for me.  Interesting website,
> BTW.

Eyeglass lenses very likely do not have a good polish of the sort that
astronomers want on their mirrors and lenses.  Eyeglass polishing
emphasizes speed and cheapness over polish quality.  In typical use, the
small amount of extra scattered light from the lens isn't noticed.  I
just don't know what sort of surface to expect on crystal ware.  The cut
faces are going to be terrible.  Don't know about the blown surfaces.
Also, isn't crystal ware rather soft glass?  Even with careful washing
and drying, it would be hard to avoid a forest of sleeks on the surface.

Mark Holm
mdholm@telerama.com


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