In the mid 2000s, Nikon and Canon broke open the DSLR camera market with a few models that crossed the $1,000 barrier, allowing photographers with a modest budget to buy professional-quality digital cameras. The D40 wasn't Nikon's first prosumer DSLR digital camera, but it was an important first for the company. Unlike its predecessor the D50, the D40 does not have an autofocus motor built in to the camera body, which causes some compatibility issues with certain lenses.
Lens Mount
The D40 uses Nikon's F-mount lens system, which means that any Nikon Nikkor lens made since the 1970s will mount to the camera. You can even attach some other, older Nikkor lenses to the D40 using adapters to expand your lens library, but most of Nikon's lenses will fit on the D40, with two key exceptions: pre-AI lenses, which date from the 1950s and 1960s, and non-AI lenses. Pre-AI lenses have a prong that connects to an aperture coupler inside older camera models, but which will stick into your camera body on the D40 and break the mirror when you try to take a picture.
Autofocus
Most of Nikon's camera lenses are called "Autofocus" or "AF" lenses. Each AF lens has further sub-classifications, such as "D," which measures distance information or "S," which stands for "silent wave motor" (a type of internal focus motor). Any Nikkor AF lens will fit on the D40, but to have full functionality with a lens, you want to make sure it has its own focus motor. AF-S and AF-I lenses have motors built in, so you don't need a camera body with a focus drive. The D40 is fully compatible with these lens types.
Non-Autofocus Lenses
You can still attach Nikkor lenses that don't have an internal autofocus system to your D40, but you can't expect them to work in all shooting modes. The D40 takes AF-D and AI lenses, which fit the lens mount and communicate with the camera, but you can't auto-focus these lenses. This means that when you have the D40 on auto mode, the camera will show you a lens error every time you half-tap the shutter. Shoot on manual, shutter priority or aperture priority modes and turn the focus selection dial to manual to use AF-D or AI lenses.
Third-party Lenses
You don't need to buy Nikon's Nikkor lenses to fit your D40. Third-party lens manufacturers built DSLR camera lenses for a variety of popular camera mounting systems. Sigma (sigmaphoto.com) and Tamron (tamron.com), for example, might make one lens and then sell it with a lens mounts for Canon, Nikon, Pentax and Sony DSLRs. These third-party manufacturers always list compatible cameras for their lenses. Don't be afraid to call Nikon and ask if a lens will work correctly before you attach it, at 800-NIKON-US.
Tags: camera body, Nikkor lenses, AF-D lenses, camera lenses, DSLR camera
