Camera Lens Parts: Focusing Ring
One of the most common camera lens parts on any SLR is the focusing ring. This is a ring on the lens body, which moves the lens elements inside the lens. By adjusting the position of the glass elements, the image produced by the lens can be brought into clear focus. Although most modern lenses feature auto-focus, they will usually have a focusing ring to allow for manual control if desired. Generally, a switch needs to be flipped from AF (auto-focus) to M (manual) to engage the focusing ring and allow for manual focus.
Third Party Lenses
When using third party lenses, such as a Leica lens on a Nikon body, the auto-focus may not be compatible. In these times, use the focusing ring to bring images into focus.
Many focusing rings have markings or a window indicating a distance. This shows the approximate distance of objects in focus for the current setting, measured from the front of the lens to the object. Its main use is for close-up photography. A common technique is to turn the focusing ring to as close of a distance as possible, then physically move the camera to focus the image.