I can speak for myself when I say that fractions and decimals make everything difficult when they come into play in and outside of math, but sadly, they appear in photography for aperture. Rob Sheppard's definition of aperture in The Magic of Digital Nature Photography is "a variable opening inside the lens that controls the amount of light coming through" (Sheppard, 52). Aperture is measured in f/stops, in which the numbers are fractions. If you understand the concept that larger denominators make the fractions smaller and small denominators make the fractions bigger, then aperture and shutter speed will be easier to grasp. In aperture, large numbers like f/16, are small apertures while small numbers like f/5.6 or f/2.8 are large apertures. Small apertures have a smaller amount of light coming in the lens, while large apertures have more light entering the lens. Aperture also affects the depth of field. According to Sheppard, "depth of field increases as you choose f/stops toward the f/22 end, and it decreases as you move toward f/2" (Sheppard, 52).
Fractions also have to make shutter speed more difficult to understand at first as well. Shutter speed influences the light coming into the lens, like aperture does, but in a different way. According to Sheppard, "shutter speed affects how long the light is allowed to come through the camera and strike the sensor" (Sheppard, 53). Shutter speed is measured in seconds and is also a fraction but can be seen as a single number, like 125. 1/125 second is twice as much as 1/250 second, so 1/125 second lets in light twice as much. Faster shutter speeds, like 1/250, will stop action in a scene but slower shutter speeds will blur a moving subject. When taking photographs without a tripod and/or having fast moving subjects, it's best to have a faster shutter speed so that the movement of your arms isn't seen as blurs in the photograph. Depending on the program/mode your camera is on, your shutter speeds may need to differ. In addition, there are different minimum shutter speeds depending on what kind of lens you are using on your camera. In the case of my camera, in which the lens is under the four thirds category and is a wide-angle lens and is 18mm and wider, my minimum would be 1/30 second. If you would like to set your own shutter speed and aperture, it's best to use the Manual Exposure setting on your camera to take better pictures in accordance to the setting.
Rob Sheppard's definition of ISO is "an international standard for film from the International Organization of Standards (ISO was chosen as a simple letter designation for certain standards, like the speed of film, it is technically not an acronym)" (Sheppard, 56). Different ISO settings have their own sensitivity to light. For example, a low ISO setting, like 100, is less sensitive to light than 400. ISO values of 100 or less give the best results with better sharpness, color, tonality, and low grain/noise, but it also means a slower shutter speed. Nature photographers with APS-C or Four Thirds cameras will use ISO 100 or less for better results, while DSLR's will use ISO settings up to 400.
In the first photograph, I my camera set to the ISO setting of 400, a shutter speed of 1/320 (because I was carrying my camera), and an aperture of f/5.6. Because of the higher ISO setting, my camera was more sensitive to the light coming into the lens, which made the photograph over exposed and the colors are really washed out. In the second photograph, I changed the ISO setting to 100, which made a big difference in how the light affected the exposure and color in the photograph. We can see that the light entry is more controlled, which helped see the colors better in the photograph and it's not so overexposed. In both photographs, the small aperture affected the depth of field, so we only see a thin line in the background of what was farther away, rather than an outline of some sort.
To wrap all of this up, what aperture, shutter speed, and/or ISO setting has been the most helpful to you for nature photography? Which have you found more difficult?
Bibliography: Sheppard, Rob. The Magic of Digital Nature Photography. New York: Lark, 2007. Print.
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