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 wave lengths; 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 com prises 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.. Patent Number 10212366. U.S.A.