When I teach photography to beginners, I spend a lot of time discussing the exposure triangle – aperture, shutter speed and ISO. Most landscape photographers use aperture priority, as depth-of-field is an important element of their composition, when they require both the foreground and background to be in sharp focus. If your camera has a large sensor, stopping down the lens may still not give you enough depth of field, especially in low-angle vertical frames. In this case I see more and more photographers using focus stacking and Tilt and Shift lenses to ensure perfect focus from front to back.
However, there are times when the shutter speed is more important to give the effect you are after. For example, with waves curling on to a beach, the best effect is often obtained at a quarter to half a second. This combines a sense of movement in the breaking water but still retains the curving shape of the wave. Alternatively, 6 or 10 stop ND filters can lengthen the shutter speed to introduce a dreamy quality to the water surface, which is a very popular look at the moment.
In the days of film you were stuck with a fixed ISO setting, depending on what film you put in your camera. One of the great advantages of digital photography is the ability to ...