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 (16,18) 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 (16,18), 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 and a rear lens axially disposed between said front lens and said image sensor, a rear surface of said front lens and a front surface of said rear lens 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 and the rear lens 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 (16,18) 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 (16,18), 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 and a rear lens axially disposed between said front lens and said image sensor, a rear surface of said front lens and a front surface of said rear lens 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 and the rear lens 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.