A method for configuring an iris imaging apparatus comprising an image sensor and an optical assembly (206, 301) including an image-side surface (303, 405) and an object-side surface (302, 404) 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 one of interposing a refractive optical element between the image-side surface of the optical assembly and the imaging surface and removing a refractive optical element from between the image-side surface of the optical assembly and the imaging surface, wherein the 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: when modifying the imaging configuration comprises interposing the refractive optical element between the image-side surface of the optical assembly and the imaging surface, the second object distance is greater than the first object distance; and when modifying the imaging configuration comprises removing the refractive optical element from between the image-side surface of the optical assembly and the imaging surface, the second object distance is less than the first object distance 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. 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 one of interposing a refractive optical element between the image-side surface of the optical assembly and the imaging surface and removing a refractive optical element from between the image-side surface of the optical assembly and the imaging surface, wherein the 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; (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: when modifying the imaging configuration comprises interposing the refractive optical element between the image-side surface of the optical assembly and the imaging surface, the second object distance is greater than the first object distance; and when modifying the imaging configuration comprises removing the refractive optical element from between the image-side surface of the optical assembly and the imaging surface, the second object distance is less than the first object distance when modifying the imaging configuration comprises interposing the refractive optical element between the image-side surface of the optical assembly and the imaging surface, the second object distance is greater than the first object distance; and when modifying the imaging configuration comprises removing the refractive optical element from between the image-side surface of the optical assembly and the imaging surface, the second object distance is less than the first object distance 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.