[ATM] Beeswax

[Jim Burrows]

At 2009-10-10 12:26 +0200, Vladimir Galogaza wrote:

>1 nm can be neglected compared to usual amount of p-v errors in figuring and
>polishing. Why then should we bother and abandon HCF use.
>What will 1 nm structured "ripple" do to image?

It might behave like a diffraction grating, so in 
some off-axis direction, there would be a maximum.

>But nevertheless, the few last strokes  are still strokes.
>Why should hexagon edges be sharp not smeared out.

The HCF hexagonal pattern has 3 sets of parallel 
edges 120° apart.  If the stroke were along one 
of these directions, the maximum action would be 
in parallel groves along those edges.  Now if you 
rotated the mirror by 60°, the stroke would be 
along another set of edges, and the mirror would 
end up with a pretty hexagonal micro-ripple.

I think it is possible that this explains the 
non-hexagonal HCF ripple shown in Tex's Fig. 
41C.1 on page 90.  A pair of groves show up which 
might be the result of the last stroke, but the 
rest of the random bumps might be coming from 
random rotations of the mirror between strokes.

And it might also be an explanation of why, as 
all the ancient experts say, don't complete 
figuring with HCF - finish with pitch.

         -- Jim Burrows
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