Nikon D40x D40X User's Manual - Page 39

Getting Good Results with Autofocus Autofocus does not perform well under the conditions listed below. The shutter release may be disabled if the camera is unable to focus under these conditions, or the in-focus indicator (z) may be displayed and the camera may sound a beep, allowing the shutter to be released even when the subject is not in focus. In these cases, use manual focus ( 28) or use focus lock ( 26) to focus on another subject at the same distance and then recompose the photograph. There is little or no contrast between the subject and the background (e.g., the subject is the same color as the background). The focus area contains objects at different distances from the camera (e.g., the subject is inside a cage). The subject is dominated by regular geometric patterns (e.g., a row of windows in a skyscraper). The focus area contains areas of sharply contrasting brightness (e.g., the subject is half in the shade). The subject appears smaller than the focus area (e.g., focus area contains both foreground subject and distant buildings). The subject contains many fine details (e.g., a field of flowers or other subjects that are small or lack variation in brightness). Reference: More on Photography (All Modes)/Focus 27