Re: [CAD_CAM_EDM_DRO] Re: Camera software

I thought of that, but I don't know enough about laser speckle to make it
work. I understood that much of laser speckle is in the optics of your eye
and is illusory in that it isn't really originating where it looks like it's
originating. As I understand it, the light is really coming from the center
of the spot and the interference pattern from the surface texture there
causes the speckle to spread out once it hits your retina.

But then I ran up against the biggest problem -- that a bright enough laser
illuminator to be seen in daylight would not be eye safe, and if you put a
tight-band filter on the imager, you can't use it for anything else.

Besides, the idea is to have a passive system using cheap off-the-shelf
parts -- the white noise projector is to get out of trouble in case we have
a lot of problems with flat, featureless surfaces.

On 8/3/06, Graham Stabler <eexgs@...> wrote:
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Elliot Burke" <elliot@...> wrote:
> >
> > Dennis,
> > If you need wideband white noise (white in the spatial frequency sense),
> > wouldn't laser speckle work for you?
>
> good idea
>
> > A laser beam passing through a piece of ground glass will project a
> > speckle pattern. Focusing the laser beam to different sizes on the
> >ground glass will change the size the speckle: small laser
> >beam->large speckle, large laser beam -> small speckle. Changing the
> >position of the ground glass slightly ( a fraction of the beam size)
> >will change the speckle pattern completely.
>
> I have used speckle illumination for wide field microscope systems, I
> used a disk of polycarbonate (perspex is fine), ground this carefully
> with some abrasive paste and mounted it on a small brushless motor.
> Spinning the disk provides a constantly evolving speckle pattern, if
> you spin fast enough this is averaged by the camera but if done more
> slowly you see streaks. Perhaps mounting the disk on a stepper motor
> so you can just change the speckle pattern as required.
>
> 3D Digitizing using cameras seems a very useful thing for lots of CNC
> users.
>
> Graham
>
>


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