Re: [ATM] Ritchey-Chrétien

["Jerry" <wa4guu@verizon.net>]

Support for Vladimir ....

I don't think you are wrong. I was just thinking of something along the
lines of what you just said.

The randomness that we are looking for in hand work only blends the work
slightly to the next zone. If you are working with a full size lap and
stroke a perfect non random 1/3 stroke, at the end of the work you can see a
clear zone of demarcation located at the extent of inward travel of the edge
of the lap on the face of the mirror. If each stroke is exactly the same it
will be a sharp slope change. By sharp I mean the change of slope will occur
at a very narrow zone.

If you stroke by hand and do a "ballpark" 1/3 stroke with some strokes
slightly longer and some slightly shorter, the demarcation becomes slightly
blurred. The change of slope will occur over a slightly wider zone.

In machine work it would be the operator of the machine who would be
responsible for making slight jogs of the position of the work to blend
zones. Some machine operators will be better at doing that than others, just
as some hand workers will do better than others.

There is no law of physics that says that randomness will be random in the
proper way to produce a better shape. You must apply order in the work to
force it to the desired shape. Constrained randomness might blur the zones
but the logical application of an ordered non-random technique can do it
too. Randomness relies somewhat on luck, doesn't it.

That seems to me to be much the same as what Vladimir said.

I occasionally say to put some randomness in, but that is not really what I
mean exactly. A short COC stroke makes zones. The W blurs the slope changes
over a wider zone. If you want some feature of the short stroke result but
don't want the over all shape or the sharp zones, you may be able to use the
W to remove what you don't want without removing what you liked about the
result of the COC stroke. That is not really random, it is mixing strokes
and doing it in an ordered fashion. That can be done on a machine too. 

I might remove the word random from my ATM vocabulary.

Jerry


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Vladimir Galogaza
Sent: Sunday, January 20, 2008 12:14 PM
To: ATM List
Subject: Re: [ATM] Ritchey-Chrétien

Some thoughts on "randomness".

Last few months worth of postings from mirror makers on the
list is enough to show that dreams of randomness are false.
For example al those w-strokes  wide and narrow, overhangs
big or small, inevitably end in advising something "accentuated".
Which is another word for non randomness.
Constant "going back to sphere", TDE's, central holes, zoning
and attempts to rectify it are witnessing that without clever thinking,
constant measurements and tests, all speaks against  hope that
randomness will automatically provide anything nearly acceptable
for ATM standards. Loosely used word "randomness" puts it in realm of urban 
legends,
similar to "Grind more worry less" proverb.
At the start of grinding, effects of factual non-randomness are invisible
because everything is rough. But at the final stages, the more we are
close to the ideal (sphere or anything else) the less we rely on randomness.
Just few strokes or few minutes of action before test, are allowed. If there

will be
real randomness, than final actions could last minute or hundreds, result 
will be always the sphere.
But nobody believes in this. People are cautious and do few strokes and lot 
of
measurements to find out where to put further non-random efforts.

Perhaps I am all wrong, but in order to see how and why,  I will appreciated
to be straightened (or supported).

Regards
Vladimir.






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