Wildlife Photography_ From Snapshots to Great Shots - Laurie Excell [19]
Figure 3.3 Setting the camera to its lowest ISO setting of 200 produced a smooth, noise-free sky.
Higher ISO settings (800, 1600, etc.) allow you to maintain a faster shutter speed or smaller aperture in low light. The resulting effect of high ISO is more noise (Figure 3.4). Even though I prefer to keep my ISO as low as I can, if raising the ISO makes the difference between capturing a sharp, noisy image and one that ends up being deleted because it is blurred due to slow shutter speeds that were unable to stop the action, I’ll choose a higher ISO. High ISO settings enable me to handhold my camera in low light.
Figure 3.4 The low light of late-evening skies forced me to increase my ISO to capture a late-night visitor outside my cabin in Alaska.
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Tip
I start every exposure by setting my ISO value first, based on the amount of light for a given scene.
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Digital Noise
Digital noise is the result of long exposures or high ISO settings and shows up the most in areas of smooth colors in both light and dark images. It is caused by heat—the longer the shutter is open, the more the sensor heats up—and by high ISO where the signal gain is increased to capture an image in low light, which causes noise. Noise is recognized as colorful “speckles” scattered throughout the image. There are a couple ways to reduce noise in these situations: using in-camera noise reduction, which I don’t recommend when photographing wildlife because it slows down the camera’s performance, and using noise-reduction software when processing the image in your computer.
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Aperture
Aperture (often referred to as an f-stop) is the size of the lens opening that allows light to pass through to the sensor. The aperture I select is so important to the appearance I am able to capture in my images that I nearly always shoot in Aperture Priority. It is also the element of the exposure triangle that is the most confusing to many people. Let’s take a look at apertures and their role in the exposure equation. The smaller the aperture number (2.8, 4.0, etc.), the bigger the lens opening (Figure 3.5). The bigger the lens opening, the more light is let through the diaphragm.
Figure 3.5 Small numbers equal less depth of field; large numbers equal more depth of field.
Wider apertures produce less depth of field (Figure 3.6) for a selective focus look and faster shutter speeds (Figure 3.7) to stop action and allow me to handhold my camera.
Figure 3.6 A wide aperture blurs the background into a palette of soft colors, making the Great Blue Heron stand out against the background.
Figure 3.7 I needed a fast shutter speed to capture the puffins sharp in mid-flight.
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Depth of Field
Depth of field is the area of acceptable sharp focus from near to infinity within an image. The aperture you select controls the depth of field in your images. In addition to aperture, depth of field is affected by distance to subject (the closer you are, the less depth of field) and the distance of the subject to the background (the closer the subject is to the background, the more “in focus” the background will appear).
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The bigger the number (f11, f16, etc.), the smaller the lens opening. Smaller apertures produce greater depth of field (Figure 3.8) and slow shutter speeds (Figure 3.9), requiring the use of a tripod for stability.
Figure 3.8 A small aperture allowed me to get all three Hooded Mergansers in focus.
Figure 3.9 A slow shutter speed created a romantic blur