Annular illuminator

DETAILED DESCRIPTION Referring to the Figure, there is shown a sectional view of a preferred embodiment of the annular illuminator of the present invention.
The annular illuminator comprises an elliptic surface 10, a cylindric surface 12 and a spheric surface 14.
All three surfaces are symmetrical with respect to the optical axis Oz and all three surfaces are surfaces of revolution about the optic axis.
A source S is located at point D which is at one focus of the ellipse on the optic axis.
The major axis 16 of the ellipse is at an acute angle .
alpha.
with respect to the optic axis.
Rays from source S which are reflected by elliptic mirror 10 would come to a focus on a circle of radius r far off the optic axis but are intercepted and reflected by cylinder 12.
Spheric surface 14 reflects rays, that would otherwise be lost, back into the illuminator system.
As shown in the Figure, the sample is located at 0, i.
e.
, x=y=z=o.
The radius of the circular cylindric surface is 1 unit, i.
e.
, y=1.
For the cross-section shown, x=o.
Therefore: 1/A=tan 50.
degree.
=1.
1918 1/B=tan 45.
degree.
=1.
0000 1/C=tan 40.
degree.
=0.
8391 E=2A F=2B G=2C A=0.
8391 B=1.
0000 C=1.
1918 E=1.
6782 F=2.
0000 G=2.
3835 Source S must lie on the optic axis Oz.
The source distance D must exceed C to avoid having the sphere reflect itself.
The sphere must extend to but not beyond line CD so that the cylinder is not directly illuminated by divergent flux.
The sphere may extend to but not beyond the line AE so that the cylinder is fully illuminated by light reflected from the ellipse.
Thus, source S must lie between C and E, i.
e.
, between 1.
1918 and 1.
6782.
It has been found that a good choice for D is about 1.
5 units.
Under these circumstances the source is located at (0, 0, 1.
5) and the center K of the ellipse is located at (0, 1, 0.
75).
The ellipse is generally described by the equation: ##EQU1## where X and Y are coordinates of an auxiliary coordinate system, a is the semimajor axis and b is the semiminor axis.
The distance from the center of the ellipse to a focus is c, where a