An iris image acquisition system comprising: 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; a processor , operably connected to said image sensor and said at least one NIR light source , to acquire image information from said image sensor under illumination at one of said different discrete NIR wavelengths; and a lens assembly comprising a front lens (12-1) and a rear lens (12-2) axially disposed between said front lens and said image sensor , a rear surface of said front lens (12-1) and a front surface of said rear lens (12-2) consisting of even aspheric surfaces to correct for field aberrations, the lens assembly having a total track length of no more than 4.7mm, the front lens (12-1) and the rear lens (12-2) each comprising a material with a refractive index inversely proportional to wavelength, said different discrete NIR wavelengths being matched with the refractive index of the material for the lens elements such that the lens assembly : balances axial image shift induced by a change in object distance with axial image shift due to change in illumination wavelength, focusses NIR light at a first NIR wavelength reflected from an iris imaged at a first object distance between about 200mm and 270mm on said image sensor ; and focusses NIR light at a second NIR wavelength, longer than said first NIR wavelength, reflected from an iris imaged at a second object distance, between about 270mm and 350mm, on said image sensor . 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; a processor , operably connected to said image sensor and said at least one NIR light source , to acquire image information from said image sensor under illumination at one of said different discrete NIR wavelengths; and a lens assembly comprising a front lens (12-1) and a rear lens (12-2) axially disposed between said front lens and said image sensor , a rear surface of said front lens (12-1) and a front surface of said rear lens (12-2) consisting of even aspheric surfaces to correct for field aberrations, the lens assembly having a total track length of no more than 4.7mm, the front lens (12-1) and the rear lens (12-2) each comprising a material with a refractive index inversely proportional to wavelength, said different discrete NIR wavelengths being matched with the refractive index of the material for the lens elements such that the lens assembly : balances axial image shift induced by a change in object distance with axial image shift due to change in illumination wavelength, focusses NIR light at a first NIR wavelength reflected from an iris imaged at a first object distance between about 200mm and 270mm on said image sensor ; and focusses NIR light at a second NIR wavelength, longer than said first NIR wavelength, reflected from an iris imaged at a second object distance, between about 270mm and 350mm, on said image sensor . balances axial image shift induced by a change in object distance with axial image shift due to change in illumination wavelength, focusses NIR light at a first NIR wavelength reflected from an iris imaged at a first object distance between about 200mm and 270mm on said image sensor ; and focusses NIR light at a second NIR wavelength, longer than said first NIR wavelength, reflected from an iris imaged at a second object distance, between about 270mm and 350mm, on said image sensor . <EOS>