Re: [ATM] Flat Tester

["Bob May" <bobmay@nethere.com>]

The beam splitter is indeed a piece of flat (stock flatness is fine) plate
glass as it is just there to reflect the light from the tested optics out to
your eye.  Nothing critical at all in any part of the system at all and a
piece of clear plastic can be used if desired.
The light source wants to be a diffused source and bare mercury vapor lamps
can be used for that if you want although the green lamps are preferred as
they are more towards the center of the eye's light sensitivity.
Single line vapor lamps of any color may be used (that includes neon bulbs
as long as they are single line ones) or you may, with reduced sensitivity
and contrast, use flourscent bulbs with a filter for one of the output
lines.
In truth, the whole design of a light box is a very broad and general one
that is more just a light block holding a light above the tested optics that
is putting out a somewhat pure color of light in a diffused fashion with an
additional optic (the flat glass at 45deg.) to bring the light out where you
can see it easily.
Another choice is a spherical mirror at the bottom of a viewer and the
reference flat top is at one focus and a eyepiece as the other focus of the
mirror with a neon bulb generating the light from a spot just out of view
beside the eyepiece.  Light goes down to the reflector and back up to the
flat surface where it is compared to the surface under test and then the
results are reflected back to the eyepiece where the fringes are seen.

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