When zoom lens are used for military sighting, the drift of optical center caused by the change of focus length will reduce the sighting accuracy severely.
长焦变焦镜头用于军事瞄准时，变焦过程中较大的光中心漂移，降低瞄准精度。
2
When the diffractive opticallens is illuminated by white light, its focal length not only relates to material dispersion and wavelength dispersion, but also to aperture factor.
在白光照射下，衍射光学透镜的焦距不仅同材料色散和波长色散有关，而且还同孔径因子有关。
3
In common physics optical experiment, single lens is used often as to wait for measuring lens in measuring of focal length.