Light Source
§Designed
to give an even irradiance over a large area on the sample.
§The
source is an quartz-halogen lamp with integral faceted ellipsoidal
reflector.
§Light
is focused on an opal glass diffuser to depolarize it, then collected by an aspheric condenser lens. An adjustable iris aperture is
used as a spatial filter to even the
illumination; this is placed at the focal plane of a Nikon 135mm camera lens, focused at infinity, which relays the light to the
sample.
§Mounted on a 3-foot optical rail which can rotate across
a range of 180 degrees to illuminate
the sample from any angle.
§The source optics are
fairly complex in order to meet the goals of good collimation, lack of polarization bias, even illumination across the
sample, and high output. 
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