Re: [ATM] ritchey cretians

["Lawrence D. Lopez" <lopez@mv.mv.com>]

Mitchell:

    It's an observation, not an ambition.

    It has been observed that many mechanical mirror making
    mechanisms turn out terrible mirrors because they are systematic.

    This doesn't mean that it can't be done or that it hasn't been done.

    By the same token humans systematically grinding mirrors have the
    same problems.

    It's only by introducing randomness in the right way that
    you get a perfect surface.

    It isn't magic.

    You are trying to get two surfaces to meet at any orientation.
    The only surfaces that do that are planes and spheres.
    Everything else is worn down.
    To meet the any orientation requirement you need to randomly
    grind in all orientations.

    This is very very basic mirror making.
   
Larry



Mitchell R wrote:
> Interesting - as a novice to this whole optical fabrication thing,
> I am not familiar with the details of current practice in design
> and using of machines for working glass, so I may be talking through
> my hat here... but why is it your ambition to never use machines to
> make mirrors? I should think that (in principle at least) it should
> be possible to make a grinding/polishing machine that would give full
> control of the profile of the work and better blending of the surface
> figure than the normal hand methods (even for glass of more modest size)...
>
>      **Quite the opposite actually. Machines do the exact same motion over
> and over and over and over (I think you get it ;) so small errors are
> multiplied many times. With hand work no two strokes will ever be exactly
> the same so they blend very nicely if you keep them all reasonably the same
> length/pressure.
>
> Mitchell 
>
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