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-S is AF 'single'- your camera will focus on a fixed object when you press the AF button and will remain focused on that point for as long as you hold the button down.This is best for static subjects.AF-C is AF 'continuous' - the camera will focus on whatever is in the relevant AF points (depending on how you have your AF coverage set up) and will attempt to keep the subject in focus wherever it moves, whether that's towards/away from the camera or laterally.F-A is AF 'auto' and automatically switches between the two AF modes depending on what the subject is doing. This requires less effort on the part of the photographer, but you are relying on the camera guessing correctly what you are focussing on, and may result in unexpected focus.