Aside from the creative ability of photography composition itself, aperture and shutter speed variability are two different mechanisms to creatively express a given scene. For a given exposure of a scene, varying either will often have a dramatic effect on the photograph. This article will explain how using aperture and shutter speed can affect your photograph.
Aperture is a method to control your depth of field. The depth of field is the area in a photograph (from front to back – foreground to background) that appears with an acceptable level of focus. In reality, the depth of field is determined by the aperture size, focal length of the lens and distance from the subject.
For a given aperture and subject distance, the depth of field will decrease with an increasing focal length of the lens. For example, the depth of field in front of and behind a tree 100 feet away at an aperture of f/4 will be much wider using a 28mm wide angle lens than with a 200mm telephoto lens. Also, for a given focal length and aperture, the closer the subject, the narrower the depth of field.
So, why would you want to “flex” your depth of field? Good question. Take a look at the picture of the squirrel. What do you notice?
It’s pretty obvious – the squirrel. Why is that? Think for a second about depth of field. In this picture, is the depth of field wide or narrow? It’s quite narrow – the depth is not much more than the squirrel himself. In fact, this picture was shot with an aperture of f/1.8 – which is considered quite a large or fast aperture. The bench posts in the foreground and background blur away to practically nothing. The sharpness of the squirrel demands your attention (the bench posts also create lines leading to and away from the squirrel, but that is another artistic point).
So, a narrow depth of field, causing a blurred background (also know as bokeh), is a technique that helps highlight a subject, or focus on a particular area of the photograph.
Now look at this picture from Peru:
Everything is in focus – from the small person in the bottom left foreground to Salkantay Peak probably miles away. What do you think my aperture was for this photograph? This was taken with a very small aperture, f/16 to be exact and the depth of field has responded accordingly. It should be pretty clear that you would use a small aperture – f/11 or smaller – for landscapes or any photograph where you want the foreground, midground and background to be in focus.
Now what about shutter speed? How would you compare the follow pictures?
Both pictures involve moving water. The waterfall creates a fluffy, soft effect with the water by using a longer shutter speed of 0.3 seconds, emphasizing the movement and flow of the water. The wave hitting the rock does just the opposite. Using a very fast shutter speed, action is frozen to the point where individual water droplets are frozen in time. Freezing the action as in the wave picture creates a more stunning effect compared with the softer waterfall.
Shutter speed is therefore a means to control how movement appears in a still picture. Lengthening the shutter time adds a blur to movement, often creating a softer effect. Remember, if you are using longer shutter times, you will need to use a tripod for support, otherwise, your own movement will blur the entire picture rendering whatever movement you were trying to capture useless! I’ve found that unless you are using a very wide angle lens (focal length in the 24mm range) any photograph with a shutter speed slower than 1/100th of a second should probably be taken with a tripod or requires image stabilization. And, as a general rule of thumb, the minimum hand-hold-able shutter speed should be the inverse of your focal length. So if you are shooting at 200mm, if your shutter speed is anything slower than 1/200th of a second, you either need a tripod or a lens with image stabilization to prevent the entire picture from being blurry.
Now what about this picture?
In this picture, the background is blurred while the horse and rider are sharper. Note to that the horse’s legs are also blurred despite being at the same depth as the rider and horse. If the background were blurred due to aperture modification, then the horse’s legs should be in the same focus as the rest of the body. This picture is an example of panning. With panning, using a slower shutter speed, the photographer moves the camera along with the moving subject. This creates a blurred background and sharp (or sharper) subject. While I completely hand held the camera for the panning in this picture, I’d advise using a tripod for a more steady and smoother pan. The skill is to move the camera at the same speed as the moving object in order to maintain the same location of the object on the camera’s sensor. This will keep the object sharp and while everything else blurs in the linear direction of the movement. For a far better example, with better technique, click here.