All lenses suffer from chromatic aberration. Its a fact that each color of light comes to a focus at different distances from the lens. If your camera lens is simple as to design, your images would be marred by a terrible rainbow fringe surrounding the outline of objects. This lens is not simple;it has been designed to mitigate chromatic aberration. This is accomplished by pairing a convex and concave lens. The convex one has a shorter focal length than needed. The concave one lengthens the overall focal length to specification. Each has opposite chromatic aberrations, thus they nearly cancel this menace. Thus, red, green and blue come to a focus at nearly the same distance downstream from the lens. Sorry to report that infrared is not corrected; it comes to a focus much further downstream. If you are imaging under IR light, you must apply a focus position correction. The red point on the lens barrel is a revised index point. In other words, you manually shift and set the distance to this index location.