Carpe Camera, Continued
In the last article we ended with a question: Why would a photographer want to take control of exposure? We have established that shutter speed settings and apertures pair up in specific ways at different light levels in order to give us a good exposure and capture our image. However shutter and aperture controls have an even greater effect on our images.
Shutter speed effects are easy to see. If the speed is too low we get blurry pictures caused by subject movement or the tiny shakes and tremors of our hands. In general, most people can reliably hand hold a camera at 1/60 of a second. However this isn’t a fast enough speed to stop the motion of somebody walking fast let alone running.
Here are a few ‘Rules of Thumb’ for shutter speeds:
• In general, a shutter speed of 1/125 or higher will usually stop the motion of somebody walking or jogging. For a runner select 1/250, for a car or plane try 1/500 and higher.
• When shooting at speeds slower than 1/60 use a tripod or monopod. Below 1/15 shooting is only suggested with a tripod.
• In order to minimize the effects of hand tremor while hand holding, select a shutter speed that is faster than “1/lens length”. In other words, on a zoom lens set to 200mm choose a shutter speed higher than 1/200. (Most newer cameras will do this for you in Program mode provided there is enough light!)
So, selecting shutter speed is important. Setting the shutter speed can have a lot of impact on how we perceive the sharpness of the subject in the final image.
On the other hand, aperture effects can be quite subtle. Aperture selections contribute to the feeling of depth in a two dimensional photograph. As the aperture is opened wider, the background behind a subject will become increasingly blurry and out of focus. This is a very useful technique that can add a feeling of depth to a two-dimensional photograph.
Not only can aperture effect the perception of depth in our images but by selecting a wider aperture the photographer can create a sense of separation between subject and background.
The effects of aperture selection also follow a few ‘Rules of Thumb’
• Very few lenses are at their sharpest at the fully open aperture setting. Most cameras tend to have the greatest degree of critical sharpness at the middle range of their aperture scale – f 5.6 to f 8.
• A landscape photographer will more often work the aperture toward the smallest size possible in order to assure great depth of focus in their images. The opposite goal of a portrait photographer.
So back to the original question about why a photographer would want to shift the camera’s chosen exposure settings. From what we have just learned, a photographer shooting in Program mode now has a reason to choose between the exposure pairings that the camera’s meter has set.
• A faster shutter speed to stop action
• A slower shutter speed to blur action
• A wider aperture to blur backgrounds
• A smaller aperture to increase background sharpness
And all of these choices can be made “on the fly” by simply rolling the Program Shift wheel.
Aperture Priority and Shutter Priority are auto-exposure modes too, however the photographer selects one value and the camera responds by selecting the other value in order to achieve exposure. (Keep in mind that the photographer has also selected the ISO setting)
Suppose that we want to shoot a portrait. In order to capture consistent subject and background focus we select “Av” mode. We then select the aperture we want to use, essentially locking in this part of the exposure calculation. In this case f 2.8 is chosen to maximize background blur.
With this setting, no matter how the light changes our aperture will remain the same.
When the photographer selects Aperture Priority Mode the camera is given two of the three exposure components – the ISO sensitivity and the desired aperture value. The camera’s computer determines the correct setting for the shutter speed to complete the exposure calculation.
Aperture Priority exposure is the most commonly used auto-exposure mode by photographers. By controlling the aperture the photographer is also controlling the sense of depth and space in an otherwise two dimensional image.
Please keep in mind that if the aperture selected is too open or too closed for the available light the camera will flash exposure warnings in the viewfinder and on the LCD menu screen. If this happens simply select another aperture value or alter the ISO setting to maintain the chosen aperture.
Selecting a shutter speed in S (Tv) Mode
In this case imagine that we are shooting a sporting event. We want to remove as much motion blur from the images as possible. We select 1/250 as our shutter speed to help assure we get the motion-stopping capability we expect.
With this setting, no matter how the light changes our shutter speed will remain the same.
Just as happened in Av Mode, when the photographer selects Shutter Priority Mode the camera is given two of the three exposure components – the ISO sensitivity and the desired shutter speed. The camera’s computer determines the correct setting for the aperture in order to complete the exposure calculation.
While Aperture Priority may be the most common auto-exposure mode selected by photographers, Shutter priority is the number one choice for sports photographers. In sports photography rendering a fast moving player in crisp, sharp focus is the goal. Capturing a sense of depth and dimension is an important but secondary concern.
Once again, if the shutter speed selected is too fast or too slow for the available light the camera will flash exposure warnings in the viewfinder and on the menu LCD. If this happens simply select another shutter speed or alter the ISO setting to maintain the chosen shutter speed.
An Important Note: Please be aware how your specific camera alerts you to a situation where you have picked an exposure combination that is outside the capabilities of the light that is present! Even in auto exposure modes it is possible to get over or under exposed images if you aren’t aware of your camera’s exposure warning symbols!
• In order to capture images that are better than “above average” the photographer can use Program, Aperture and Shutter priority modes.
• The photographer can choose these modes to select a specific component in the camera’s exposure calculation in order to create the effect desired.
• Program mode allows for shifting between various combinations of aperture and shutter that yield the same exposure. The “Program Shift Wheel” is the dial that provides this control.
• For even tighter control the photographer can select to control two of the three exposure controls allowing the camera to automatically respond with the correct setting on the third control.
• Aperture Priority Mode to control depth of field
• Shutter Priority Mode to control motion blur
There are many next steps that can enhance your photography:
• Learn about exposure compensation
• Add an automatic flash into your shooting
• For sport shooters, learn about the “peak of action” and how it can help stop motion
• For portrait or still life shooters learn how the distance between subject and background further increases the blurring effect of a wide aperture.
Future articles in this series will cover exposure compensation as well as discuss aperture and shutter priority plus full manual exposure modes in greater depth.
Editor’s Note: We tried to avoid using the phrases ‘proper exposure’ or ‘correct exposure’, this was not an omission. While there are images that are obviously under- or over-exposed, the judgment of good or bad is entirely subjective. Exposure variations are important tools in creative photography often used to focus attention on (or direct it away from) elements in the scene.