Abstract: An iris image acquisition system for a mobile device, comprises a lens assembly arranged along an optical axis and configured for forming an image comprising at least one iris of a subject disposed frontally to the lens assembly; and an image sensor configured to acquire the formed image. The lens assembly comprises a first lens refractive element and at least one second lens element for converging incident radiation to the first refractive element. The first refractive element has a variable thickness configured to counteract a shift of the formed image along the optical axis induced by change in iris-lens assembly distance, such that different areas of the image sensor on which irises at different respective iris-lens assembly distances are formed are in focus within a range of respective iris-lens assembly distances at which iris detail is provided at sufficient contrast to be recognised.

Abstract: An iris image acquisition system for a mobile device, comprises a lens assembly arranged along an optical axis and configured for forming an image comprising at least one iris of a subject disposed frontally to the lens assembly; and an image sensor configured to acquire the formed image. The lens assembly comprises a first lens refractive element and at least one second lens element for converging incident radiation to the first refractive element. The first refractive element has a variable thickness configured to counteract a shift of the formed image along the optical axis induced by change in iris-lens assembly distance, such that different areas of the image sensor on which irises at different respective iris-lens assembly distances are formed are in focus within a range of respective iris-lens assembly distances at which iris detail is provided at sufficient contrast to be recognised.

Abstract: An iris image acquisition system comprises an image sensor comprising an array of pixels including pixels sensitive to NIR wavelengths; at least one NIR light source capable of selectively emitting light with different discrete NIR wavelengths; and a processor, operably connected to the image sensor and the at least one NIR light source, to acquire image information from the sensor under illumination at one of the different discrete NIR wavelengths. A lens assembly comprises a plurality of lens elements with a total track length no more than 4.7 mm, each lens element comprising a material with a refractive index inversely proportional to wavelength. The different discrete NIR wavelengths are matched with the refractive index of the material for the lens elements to balance axial image shift induced by a change in object distance with axial image shift due to change in illumination wavelength.

Abstract: An iris image acquisition system comprises an image sensor comprising an array of pixels including pixels sensitive to NIR wavelengths; at least one NIR light source capable of selectively emitting light with different discrete NIR wavelengths; and a processor, operably connected to the image sensor and the at least one NIR light source, to acquire image information from the sensor under illumination at one of the different discrete NIR wavelengths. A lens assembly comprises a plurality of lens elements with a total track length no more than 4.7 mm, each lens element comprising a material with a refractive index inversely proportional to wavelength. The different discrete NIR wavelengths are matched with the refractive index of the material for the lens elements to balance axial image shift induced by a change in object distance with axial image shift due to change in illumination wavelength.