Overview General Information Nikon manufactures five lens converters for modifying the on-camera focal length. The following image shows all five Nikon lens converters. All of these lens converters screw on the on-camera lens and change the combined focal lengths. The following table gives the range of the combined focal length of each converter. 3 x 114mm - 345mm Please keep in mind that these lens converters are of type afocal .
Parallel lights entering an afocal lens are also parallel when they exit.
Thus, an afocal lens does not have focal length, or, its focal point is at infinity. As a result, afocal lens are only used to modify focal lengths and other optical characteristics and must be used with other prime lenses. This means afocal lens are not supposed to be used alone. These include lens flare, ghost image, field curvature, aberration and so on. Please refer to On-Camera Lens Overview for the details.