Most cameras produced these days have varying forms of automation. There are Full Auto mode, Program (P) mode, Aperture Priority (AV) mode, Shutter Priority (TV) mode, Manual (M) mode and some cameras have a multitude of special Program modes like Portrait, Landscape, Close-up, Action, etc.
The method of using apertures/shutter speeds outlined above is generally suitable for cameras with the Manual (M) mode. In other modes, any change in either the aperture (in AV mode) or the shutter speed (TV mode) will be compensated for by the camera’s internal computer. For example, if you have your camera set to AV mode, and has decided that you want lots of depth of field in your image, and you have set your aperture to f/11 (aperture priority), the camera will select a shutter speed to give what it computes to be the correct exposure. Likewise, if you have your camera set to TV mode, and have decided that you want a shutter speed of 1/250 second (shutter priority) to freeze movement, again the camera will set an aperture to give what it computes to be the correct exposure.
In Program (P) mode, most cameras set both the aperture and shutter speed for what it computes to be optimum exposure. However, most cameras also have what is called “Program Shift” which is a facility whereby if you change one of the settings, say the aperture setting, the camera will automatically compensate by changing the other setting for you. This is very useful and could be seen to be an alternative method to using AV or TV modes.
In the other modes, i.e. Full Auto and special Program modes, there is not usually any adjustment to the camera settings possible.
Finally, whilst all settings may be changed as outlined above, be aware that the camera will not be able to make settings outside the capability of the lens or camera. For example, if you wanted to use a higher shutter speed than suggested, and the resulting aperture was outside the range of the lens, lights would flash in the viewfinder to warn you of the fact. Likewise, if you wanted a large aperture and the resulting shutter speed was out of the camera’s range, you would also be warned.
