Method and apparatus for visualizing phase object

1. A visualization method comprising:

illuminating an observation target object in an oblique illumination to acquire a plurality of first electronic images of the observation target image illuminated from different illumination directions; and

calculating the plurality of first electronic images to generate a second electronic image;

wherein the observation target object is illuminated in an oblique illumination such that 0.4≦d/r, where d denotes a distance between a pupil center of an image forming optical system and a position where light entering the image forming optical system at a position closest to the pupil center of the image forming optical system passes through a pupil of the image forming optical system, and r denotes a pupil radius of the image forming optical system.

2. The visualization method according to claim 1 , wherein acquiring the plurality of first electronic images comprises:

acquiring a first electronic image of the observation target image illuminated in an oblique illumination from a first illumination direction; and

acquiring a first electronic image of the observation target image illuminated in an oblique illumination from a second illumination direction,

wherein the first illumination direction and the second illumination direction are substantially symmetric with respect to an optical axis of an illumination optical system configured to illuminate the observation target object.

3. The visualization method according to claim 1 , further comprising, before acquiring the plurality of first electronic images, displacing the observation target object, in a direction of an optical axis of the image forming optical system, from a focal position of the image forming optical system where an optical image of the observation target object is formed.

4. The visualization method according to claim 1 , wherein generating the second electronic image comprises calculating a difference between the plurality of first electronic images.

5. The visualization method according to claim 1 , wherein acquiring the plurality of first electronic images comprises:

illuminating the observation target object in an oblique illumination from a first illumination direction;

illuminating the observation target object in an oblique illumination from a second illumination direction;

acquiring a first electronic image of the observation target object illuminated in an oblique illumination from the first illumination direction; and

acquiring a first electronic image of the observation target object illuminated in an oblique illumination from the second illumination direction,

wherein the first illumination direction and the second illumination direction are substantially symmetric with respect to an optical axis of an illumination optical system configured to illuminate the observation target object.

6. The visualization method according to claim 1 , wherein acquiring the plurality of first electronic images comprises:

illuminating the observation target object in an oblique illumination simultaneously from a first illumination direction and from a second illumination direction;

acquiring a first electronic image of the observation target object illuminated in an oblique illumination from the first illumination direction; and

acquiring a first electronic image of the observation target object illuminated in an oblique illumination from the second illumination direction,

wherein the first illumination direction and the second illumination direction are substantially symmetric with respect to an optical axis of an illumination optical system configured to illuminate the observation target object.

7. A visualization apparatus comprising:

a light source;

an illumination optical system configured to guide light from the light source to an observation target object;

an image forming optical system configured to form an optical image of the observation target object on an image plane;

an image pickup element arranged on the image plane;

a calculation device configured to calculate a plurality of first electronic images of the observation target object obtained from the image pickup element to generate a second electronic image; and

an oblique illumination control section configured to control an illumination direction of oblique illumination provided by the illumination optical system,

wherein the plurality of first electronic images include first electronic images of the observation target object illuminated from different illumination directions by the oblique illumination control section;

wherein the oblique illumination control section comprises an oblique illumination section arranged near or at a pupil of the illumination optical system and comprising a plurality of apertures configured to define an illumination angle of the oblique illumination; and

wherein 0.4≦s d/r, where d denotes a distance between a pupil center of the image forming optical system and an aperture end of each of a plurality of aperture images obtained by projecting the plurality of apertures at a pupil position of the image forming optical system, the aperture end being closest to the pupil center, and r denotes a pupil radius of the image forming optical system.

8. The visualization apparatus according to claim 7 , wherein the plurality of first electronic images include:

a first electronic image of the observation target image illuminated from a first illumination direction; and

a first electronic image of the observation target image illuminated from a second illumination direction,

wherein the first illumination direction and the second illumination direction are substantially symmetric with respect to an optical axis of the illumination optical system.

9. The visualization apparatus according to claim 7 , wherein the image forming optical system is arranged in such a manner that a focal position of the image forming optical system is displaced from the observation target object.

10. The visualization apparatus according to claim 7 , wherein the calculation device calculates a difference between the plurality of first electronic images to generate the second electronic image.

11. The visualization apparatus according to claim 7 , wherein the oblique illumination control section further comprises:

a first polarizer arranged over a first one of the plurality of apertures to allow light in a first polarizing direction to pass through;

a second polarizer arranged over a second one of the plurality of apertures to allow light in a second polarizing direction orthogonal to the first polarizing direction to pass through; and

a polarizing direction control section arranged between the light source and both the first polarizer and the second polarizer to control the polarizing direction of light,

wherein the first polarizer and the second polarizer are arranged substantially symmetrically with respect to an optical axis of the illumination optical system.

12. The visualization apparatus according to claim 7 , wherein the plurality of apertures comprises at least a first aperture and a second aperture, and the first aperture and the second aperture are arranged substantially symmetrically with respect to an optical axis of the illumination optical system, and

wherein the light source comprises:

a first light source configured to illuminate the first aperture; and

a second light source configured to illuminate the second aperture.

13. The visualization apparatus according to claim 7 , wherein the oblique illumination control section further comprises:

a first optical filter arranged over a first one of the plurality of apertures to allow light in a first wavelength region to pass through; and

a second optical filter arranged over a second one of the plurality of apertures to allow light in a second wavelength region different from the first wavelength region to pass through,

the first optical filter and the second optical filter are arranged substantially symmetrically with respect to an optical axis of the illumination optical system, and

the image pickup element comprises:

a plurality of first-pixels configured to detect the light in the first wavelength region; and

a plurality of second pixels configured to detect the light in the second wavelength region.

14. The visualization apparatus according to claim 7 , wherein the oblique illumination control section further comprises:

a first polarizer arranged over a first one of the plurality of apertures to allow light in a first polarizing direction to pass through; and

a second polarizer arranged over a second one of the plurality of apertures to allow light in a second polarizing direction orthogonal to the first polarizing direction to pass through;

wherein the first polarizer and the second polarizer are arranged substantially symmetrically with respect to an optical axis of the illumination optical system, and

the image pickup element comprises:

a plurality of first pixels configured to detect the light in the first polarizing direction; and

a plurality of second pixels configured to detect the light in the second polarizing direction.

15. The visualization apparatus according to claim 7 , further comprising a display device configured to display the second electronic image generated by the calculation device.