RE: [ATM] Star test with laser light sources

[Woodchuck <djv@bedford.net>]

On Mon, 26 Jul 2004, Jerry wrote:

>
> I have no first hand knowledge. Are you trying to "see" or "image" the
> rings?
>
> Why not just use an incandescent light? Must you have monochromatic light?

Certainly not for Foucault null testing on a mirror!

> The monochromatic nature of the laser may be causing you trouble such as the
> speckles and rings. Or those speckles you couldn't remove might be pits...
> Nah! Just dust on the surface and strange diffraction effects with the dust
> from the monochromatic light. Alternatively the grain of the steel ball may
> be causing you to see a "cluster" of stars on the ball surface.
>
> Jerry

One of the ATM books reports polishing the steel ball against
a pitch lap with rouge (presumably by pitching the ball to a stick
and using a spinning lap, as in polishing small lenses), and that
this solved a similar speckling problem.  An impromptu vertical
spindle is easily rigged up using a hand-held electric drill, and
a lap should be fairly obvious.  What was being polished away here
(steel, gunk-crud, iron oxide, grease/oil) may be unknown, but it
worked for that fellow.

I seem to recall that when using incandescant lights, one wants
to focus an image of the filament on the ball; I don't know if this is
necessary.

Some use the Sun as the light source, and some use little aluminized
spheres (Christmas tree ornaments) as the sphere.

Dave

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