Microscope illuminator

1 . A microscope, comprising:

a base;

a slide holder coupled to the base and configured to accept a slide;

an illuminator movably coupled to the base and comprising a light emitting diode (LED) having a light-emitting surface configured to project light on an optical path toward the slide with a separation distance between the light-emitting surface and the slide when the slide is accepted by the slide holder; and

an objective coupled to the base and disposed so as to observe a portion of the slide illuminated by the projected light;

wherein:

there is no light-shaping optical element disposed on the optical path between the illuminator and the slide holder;

the objective has a Field of View (FOV);

the projected light has a peak intensity on an axis perpendicular to the light-emitting surface and a 90% intensity at a determined half-angle from the perpendicular axis; and

the projected light has an intensity over the entire FOV that is within a range of 10% of the peak intensity when the separation distance is at least the arcsine of the half-angle.

2 . The microscope of claim 1 , wherein the illuminator can be moved along the optical path.

3 . The microscope of claim 2 , wherein:

the objective has an aperture and an acceptance angle;

the projected light reaches the aperture of the objective within an arrival angle that is inversely related to the separation distance; and

increasing the separation distance reduces the arrival angle of the projected light that enters the aperture of the objective, thereby reducing a realized numerical aperture of the microscope.

4 . The microscope of claim 3 , wherein changing the separation distance changes the realized numerical aperture of the microscope.

5 . The microscope of claim 2 , wherein:

the illuminator has an adjustable intensity; and

the intensity is adjusted automatically based in part on the separation distance.

6 . The microscope of claim 5 , wherein the intensity is adjusted automatically to maintain a selected brightness as the separation distance is changed.

7 . The microscope of claim 1 , wherein the projected light is essentially grainless.

8 . An illuminator for use with a microscope having a base, a slide holder configured to accept a slide, and an objective having a Field Of View (FOV) covering a portion of an accepted slide, the illuminator comprising a light-emitting surface and configured to be movably coupled to the base, wherein a clear and focused image can be provided by the objective with no light-shaping optical element disposed along an optical path from the illuminator to the accepted slide;

wherein:

the illuminator is movable with respect to the base to selectably determine a separation distance between the light-emitting surface and the slide;

the light emitting surface configured to project light on the optical path;

the projected light has a peak intensity on an axis perpendicular to the light-emitting surface and a 90% intensity at a determined first half-angle from the perpendicular axis;

the projected light has an intensity over the entire FOV that is within a range of 10% of the peak intensity when the separation distance is at least the arcsine of the half-angle.

9 . The illuminator of claim 8 , wherein changing the separation distance changes the realized numerical aperture of the microscope.

10 . A method of operating a microscope, comprising:

projecting light from a planar light-emitting surface directly onto an underside of a slide accepted by the microscope; and

adjusting a separation distance between the light-emitting surface and the underside of the slide to achieve a selected value of a realized numerical aperture of the microscope;

wherein:

the light emitted by the light-emitting surface has an intensity that is uniform within a defined range over a dispersion cone having a defined half-angle;

the projected light is not shaped between the light-emitting surface and the underside of the slide; and

increasing the separation distance reduces a maximum half-angle of the emitted light that enters an entrance aperture of an objective of the microscope.

11 . The method of claim 10 , wherein:

the light-emitting surface comprises a light emitting diode (LED); and

reduces the maximum half-angle of the emitted light that enters the entrance aperture of the objective reduces the realized numerical aperture of the microscope.