Optimized imaging apparatus for iris imaging

1. A method for configuring an imaging apparatus comprising an image sensor and an optical assembly including an image-side surface and an object-side surface and configured for imaging an object plane onto an imaging surface of the image sensor, the method comprising:

modifying a first imaging configuration of the imaging apparatus to achieve a second imaging configuration of said imaging apparatus, wherein modifying the first imaging configuration comprises interposing a refractive optical element between the image-side surface of the optical assembly and the imaging surface, wherein the interposed refractive optical element is configured to:

(i) shift an image-side principal plane of the optical assembly, by a shift distance in the direction of the imaging surface; and

(ii) shift an image-side focal plane of the optical assembly, by the shift distance in the direction of the imaging surface;

wherein in the first imaging configuration, the optical assembly images onto the imaging surface, an in-focus image of an object positioned at a first object plane located a first object distance away from the object-side surface of the optical assembly;

wherein in the second imaging configuration the optical assembly images onto the imaging surface, an in-focus image of an object positioned at a second object plane located a second object distance away from the object-side surface of the optical assembly, such that the second object distance is greater than the first object distance;

and wherein the shift distance is a distance between a first image plane at which the optical assembly images an in-focus image of an object positioned at the first object plane, and a second image plane at which the optical assembly images an in-focus image of an object positioned at the second object plane.

2. The method as claimed in claim 1 , wherein width and refractive index of the refractive optical element are selected such that the image-side principal plane and image-side focal plane of the optical assembly shift in the direction of the imaging surface, by the shift distance.

3. The method as claimed in claim 1 , wherein one of the first and second imaging configurations is optimized for iris imaging.

4. The method as claimed in claim 3 , wherein the first imaging configuration is optimized for iris imaging.

5. The method as claimed in claim 1 , wherein the optical assembly is a fixed focus optical assembly.

6. The method as claimed in claim 1 , wherein at least one of:

focal length of the optical assembly, and

distance between the imaging surface and the image-side surface of the optical assembly, is constant in both of the first and second imaging configurations.

7. A method for configuring an imaging apparatus comprising an image sensor and an optical assembly including an image-side surface and an object-side surface and configured for imaging an object plane onto an imaging surface of the image sensor, the method comprising:

modifying a first imaging configuration of the imaging apparatus to achieve a second imaging configuration of said imaging apparatus, wherein modifying the first imaging configuration comprises removing a refractive optical element from between the image-side surface of the optical assembly and the imaging surface, wherein the removed refractive optical element is configured to:

(i) shift an image-side principal plane of the optical assembly, by a shift distance in the direction of the imaging surface; and

(ii) shift an image-side focal plane of the optical assembly, by the shift distance in the direction of the imaging surface;

wherein in the first imaging configuration, the optical assembly images onto the imaging surface, an in-focus image of an object positioned at a first object plane located a first object distance away from the object-side surface of the optical assembly;

wherein in the second imaging configuration the optical assembly images onto the imaging surface, an in-focus image of an object positioned at a second object plane located a second object distance away from the object-side surface of the optical assembly, such that the first object distance is greater than the second object distance;

and wherein the shift distance is a distance between a first image plane at which the optical assembly images an in-focus image of an object positioned at the first object plane, and a second image plane at which the optical assembly images an in-focus image of an object positioned at the second object plane.

8. The method as claimed in claim 7 , wherein width and refractive index of the refractive optical element are selected such that the image-side principal plane and image-side focal plane of the optical assembly shift in the direction of the imaging surface by the shift distance.

9. The method as claimed in claim 7 , wherein one of the first and second imaging configurations is optimized for iris imaging.

10. The method as claimed in claim 9 , wherein the refractive optical element is a plano-parallel element.

11. The method as claimed in claim 9 , wherein the refractive optical element is a plano-parallel optical filter.

12. The method as claimed in claim 11 , wherein when the first imaging configuration is optimized for iris imaging, the optical filter is an infra-red pass filter.

13. The method as claimed in claim 11 , wherein when the second imaging configuration is optimized for iris imaging, the optical filter is an infra-red cut filter.

14. The method as claimed in claim 7 , wherein the optical assembly is a fixed focus optical assembly.

15. The method as claimed in claim 7 , wherein at least one of:

focal length of the optical assembly, and

distance between the imaging surface and the image-side surface of the optical assembly, is constant in both of the first and second imaging configurations.

16. An imaging apparatus configured for switching from a first imaging configuration to a second imaging configuration, the apparatus comprising:

an image sensor comprising an imaging surface;

an optical assembly including an image-side surface and an object-side surface and configured for imaging an object plane onto an imaging surface of the image sensor such that:

in the first imaging configuration, the optical assembly images onto the imaging surface, an in-focus image of an object positioned at a first object plane located a first object distance away from object-side surface of the optical assembly;

in the second imaging configuration, the optical assembly images onto the imaging surface, an in-focus image of an object positioned at a second object plane located a second object distance away from the object-side surface of the optical assembly; and

the second object distance is greater than the first object distance;

a refractive optical element configured to be interpositioned between the image-side surface of the optical assembly and the image sensor to switch from the first imaging configuration to the second imaging configuration, such that the interpositioned refractive optical element:

(i) shifts an image-side principal plane of the optical assembly, by a predefined shift distance in the direction of the imaging surface; and

(ii) shifts an image-side focal plane of the optical assembly, by the shift distance in the direction of the imaging surface;

wherein the shift distance is a distance between a first image plane at which the optical assembly images an in-focus image of an object positioned at the first object plane, and a second image plane at which the optical assembly images an in-focus image of an object positioned at the second object plane.

17. The imaging apparatus as claimed in claim 16 , wherein the refractive optical element is configured to be removed from between the image-side surface of the optical assembly and the imaging surface to achieve the first imaging configuration.

18. The imaging apparatus as claimed in claim 17 , wherein width and refractive index of the refractive optical element are selected such that the image-side principal plane and image-side focal plane of the optical assembly shift in the direction of the imaging surface, by the shift distance.

19. The imaging apparatus as claimed in claim 17 , wherein one of the first and second imaging configurations is optimized for iris imaging.

20. The imaging apparatus as claimed in claim 19 , wherein the refractive optical element is a plano-parallel element.

21. The imaging apparatus as claimed in claim 19 , wherein the refractive optical element is a plano-parallel optical filter.

22. The imaging apparatus as claimed in claim 21 , wherein when the first imaging configuration is optimized for iris imaging, the optical filter is an infra-red pass filter.

23. The imaging apparatus as claimed in claim 21 , wherein when the second imaging configuration is optimized for iris imaging, the optical filter is an infra-red cut filter.

24. The imaging apparatus as claimed in claim 16 , wherein the optical assembly is a fixed focus optical assembly.

25. The imaging apparatus as claimed in claim 16 , wherein at least one of:

focal length of the optical assembly, and

distance between the imaging surface and the image-side surface of the optical assembly is constant in both of the first and second imaging configurations.