Parts of a Camera Lens: Adapter
A camera lens adapter allows photographers to use lenses which were not designed to be used with their cameras. Every camera manufacturer has a unique mount to attach their lenses to their cameras. Sometimes, manufacturers have multiple mounts, such as Canon with their EF and EF-S lines of lenses. However, there may be times when a photographer will wish to use a lens that does not fit directly onto his camera body. For example, many photographers like to use Leica lenses, even though they do not own a Leica camera body. A lens adapter attaches to the lens on one end and to the camera body on the other, mounting the lens onto the camera.
Use of an Adapter
Adapters must be specifically designed for both the camera and the lens. Photographers need to know specifications for both the lens to be adapted, and the camera body to be used. For example, an adapter may convert a Nikon Nikkor lens to fit a Canon EOS. Since they must be specific, adapters may list the lenses and bodies for which they will work.
Disadvantages of an Adapter
Adapters move the lens farther away from the camera body, so there will be a magnification factor. This means that the edges of the viewable area will be cut off, and that there will be a zoom effect. For example, a 50mm lens on an adapter may give the image of a 70mm lens.
Also, electronic communication is usually not possible through an adapter. Manual focus and aperture adjustments are generally required.