Nikon makes over 200 different types of optical glass for its extensive line of lenses. Nikon uses this glass to manufacture its DX and non-DX camera lenses. Nikon designed its DX lens line to meet the needs of consumers using the company's smaller format line of cameras. DX lenses offer you Nikon quality at a price comparable to third-party lens manufacturers.
DX vs. FX
Nikon makes two digital SLR camera sensor sizes -- DX and FX. FX sensors represent a sensor size equivalent to a frame of 35 mm film, or 36 mm by 24 mm in size. The DX sensor measures only 24 mm by 16 mm in size. This smaller sensor utilizes only a portion of the field of view of a lens designed to fit on an FX sensor camera body. Nikon has designed a family of lenses to specifically fit the smaller frame, DX camera bodies. These lenses have a "DX" designation on the lens body and also in the naming convention of the lens, such as the AF-S DX Nikkor 35 mm f/1.8G.
Why DX Lenses?
Because Nikon has designed the DX lens line to work specifically with the company's DX camera bodies, the lenses are lighter weight and less expensive than lenses made for full-frame FX bodies. Lenses designed for Nikon full-frame bodies typically cost a premium over DX lenses because of the additional manufacturing cost associated with their production. Additionally, DX body cameras like the Nikon D90, D3100 and D5000 can also accommodate full-frame non-DX lenses. Although some functionality may get lost during use -- auto-focus and some metering modes -- the ability to use non-DX lenses opens up the available lens options for DX camera owners.
The Crop Factor
Because DX camera bodies have smaller sensors than a standard frame of 35 mm film, any lens used on a DX body must have a crop factor applied to its focal length. In essence, any lens used on a DX camera, including DX and non-DX lenses, must have the focal length multiplied by a factor of 1.5X. The crop factor approximates the focal length of the lens as if it were used on a 35 mm full-frame FX body camera. For instance, a 100 mm lens on an FX body has a field of view that reflects its focal length of 100 mms. Put the same lens on a DX body and the field of view no longer resembles a 100 mm lens but a 150 mm lens. That's because on the DX body the focal length, 100 mm, is multiplied by a factor of 1.5, making the 100 mm lens view like a 150 mm lens.
Considerations
DX lenses certainly have a few factors in their favor -- less cost and less weight being the two biggest. However, DX lenses don't come in as many different varieties and specialties as non-DX lenses. For example, an architectural photographer typically requires lenses that have tilt/shift or perspective control movements. These movements aren't available in DX lenses. Also, as of early 2011 Nikon doesn't make any super-telephoto lenses in the DX format.
Tags: focal length, non-DX lenses, camera bodies, field view, lens body, Nikon designed