As described in Chapter 6, the skeleton is divided into axial and appendicular portions (see Figures 6.1 and 7.1). The axial skeleton is structured from 80 bones segregated intothree major regions: the skull, vertebral column, and thoraciccage (Figure 7.1) . This part of the skeleton (1) forms the lon-gitudinal axis of the body, (2) supports the head, neck, and Chapter 7 The Skeleton 199 7 Figure 7.1 The human skeleton.
Above: Some cameras have a switch to set it to auto or manual focus. Manual focus, meanwhile, disables autofocus and enables you to adjust it yourself. This is useful when the focusing system can't find focus for whatever reason, such as when it's too dark or when there's little contrast in the scene.
AF and AF-S NIKKOR Lenses. We know there are two series of autofocus lenses: AF NIKKOR and AF-S NIKKOR. Both AF and AF-S NIKKOR lenses can also be used in manual focusing mode. AF NIKKOR lenses use a mechanical coupling between the lens and the camera body. On several Nikon DSLR camera bodies, the focus motor is in the camera and a series of gears drives the lens' focusing mechanism, which allows the lens to focus. Autofocus (AF and AF-S lenses) are further categorized into G-type or D-type lenses.