of the picture than say f4 over the same focal length.
Depth of field can also be increased or decreased by using different focal lengths. Depth of field increases when we use wide-angle lenses and it decreases when we use longer focal length lenses, a 200mm lens for example.
However, remember that it isn’t simply a matter of increasing or decreasing the aperture. Simply changing the f number can give you over or under exposed photos. The aperture and the shutter speed have an inverse relationship in continuous light, that is, the bigger the aperture, the faster should be the shutter speed and vice-versa. Suppose you have set your correct exposure for a shot to f16 aperture and 1/125 shutter speed. You then realise that you need to step down the aperture to f2.8 because you want only the subject in focus. This means that you will open up the aperture by five full stops from f16 (11-8-5.6-4-2.8). For the exposure to remain correct, you will correspondingly have to increase the shutter speed by five full stops from 1/125: 1/250-1/5001/1000-1/2000-1/4000. At an aperture of f2.8 you will require a shutter speed of 1/4000 to maintain the original exposure.
When using flash, you will have to control the exposure by increasing or decreasing the light intensity or moving the light source away or closer to the object.