Compact system for presenting wide field object target to test optic or system
Apparatus for evaluating optical components and systems that uses a precision compact mirror support structure to present to an optical system or electro-optical system (e.g., a camera) multiple images of at least one optical evaluation target over a wide field to allow assessment of the performance or alignment of the optical or electro-optical system over its intended field of use. The mirror support structure generates multiple images of an optical evaluation target by providing multiple folded optical paths between the target and the desired field locations of the test optic. The mirrors employed may either be parallel or at angles with respect to one another.
1. Apparatus for providing a plurality of images of at least one optical evaluation target over a predetermined field of use of a test optic, said apparatus having an optical axis and comprising:
a generally hollow mirror support structure, said hollow mirror support structure having entrance and exit apertures in line along the optical axis, said generally hollow mirror support structure having a plurality of individual mirror mounts positioned around the optical axis with each mount arranged to locate each mirror at a predetermined angle with respect to the optical axis, each individual mirror mount having at least three points sufficient to establish the planar location and angular orientation of its corresponding mirror, said hollow mirror mount support structure also having a deterministic reference plane with which the optical axis is precisely aligned; and
a plurality of mirrors one each of which is placed in a corresponding one of said mirror mounts, the length of said apparatus along the optical axis, the position and orientation of said mirrors with respect to the optical axis and said entrance and exit apertures being such that said apparatus generates multiple images of an optical evaluation target apparent through said entrance aperture by providing multiple folded optical paths between the optical evaluation target arid the desired field locations of the test optic.
2. The apparatus of claim I wherein said generally hollow mirror support structure includes a mounting base in which said entrance aperture is formed and from which said mirror mounting planar frames depend.
3. The apparatus of claim 2 wherein said mirror mount support structure is machined of a single piece of material to provide built-in dimensional precision and thermal stability.
4. The apparatus of claim 3 wherein said single piece of material is aluminum.
5. The apparatus of claim 2 wherein said mounting base is generally perpendicular to the optical axis.
6. The apparatus of claim 1 wherein said mounting base further comprises a three point adjustable ball mount by which said mounting base can be adjusted to be parallel with respect to a reference flat.
7. The apparatus of claim 1 wherein said mirrors are parallel to the optical axis so that the off axis images formed thereby all lie in flat field.
8. The apparatus of claim 1 wherein said generally hollow mirror mount support structure is generally in the form of a truncated polyhedron that is tapered along the optical axis from said entrance aperture to said exit aperture and wherein said individual mirror mounting planar frames lie in planes at predetermined angles with respect to the optical axis so that the plurality of off axis field images generated by said apparatus lie in a slightly curved spherical surface that sags from a plane by a known amount.
9. The apparatus of claim 8 wherein said sag is approximately given by:
S
=
W
E
2
2
L
(
1
+
W
L
W
E
-
W
L
)
=
W
E
(
W
E
-
W
L
)
2
L
where:
W E is the width of said entrance aperture near an optical evaluation target'
W L is the width of exit aperture near a lens under test'
L point where the entrance pupil of the apparatus is located with respect to said exit aperture.
10. The apparatus of claim 1 further including and auxiliary focusing lens located between said apparatus and the optical evaluation target to alter the apparent location of the optical evaluation to create a virtual image of the optical evaluation target at an appropriate distance relative to the end of said apparatus.
11. The apparatus of claim 1 further including an auxiliary focusing lens located between said apparatus and the test lens to alter the apparent location of the optical evaluation to create a virtual image of the optical evaluation target at an appropriate distance relative to the end of said apparatus.
12. The apparatus of claim 1 further including a plurality of said apparatus arranged in serial fashion to allow for insertion or removal of optical evaluation targets to provide testing at different object conjugates.
13. The apparatus of claim 1 further including at least one optical evaluation target positioned near said entrance aperture and selected from the group comprising fishtails, lines, crosses, star targets, sinusoidals, pinholes, checkerboards, dots, and USAF resolution patterns.
14. The apparatus of claim 1 wherein the number of paths along which images propagate is given by:
[tanΘ] L/W=N− 1,
where L is the length of said apparatus. W is the width of said entrance aperture, N is the number of paths, and Θ is the semi-field angle for the path of the second mirror bounce of said apparatus.
15. The apparatus of claim 1 further including a fixture for mounting a test optic with respect to said exit aperture.
16. The apparatus of claim 1 further including a fixture for mounting a test optic and an auxiliary lens with respect to said exit aperture.
17. The apparatus of claim 1 further including a fixture for mounting a test optic with respect to said exit aperture and an auxiliary lens with respect to the entrance aperture.