Nikon digital SLRs have either an FX or a DX sensor. The FX sensor, measuring 24x36mm, is roughly equivalent to the size of the 35mm film frame. The DX sensor is smaller, measuring 15.8x23.6mm.
DX-NIKKOR lenses are engineered and optimized for use on Nikon DX-format D-SLRs and are designed to cover the smaller image area of the DX sensor. When a DX lens is mounted on an FX-format Nikon D-SLR, the camera’s DX-Crop Mode is automatically engaged, introducing a 1.5x magnification (cropping) factor.
Nikon digital SLR cameras that utilize the DX-format imaging sensor are designed as smaller camera bodies than those utilizing the larger FX-format sensor. Therefore, DX-format NIKKOR lenses can be made smaller as well. Because fewer materials are used, these lenses are less costly to produce.
The FX/35mm lenses are designed for use on Nikon digital SLR cameras that utilize the FX-format or 35mm full frame imaging sensor.
To learn more about the DX and FX formats, click here.