Earlier this month I completed my first trip to photograph coastal bears in British Columbia. While I've had experience with their interior cousins this turned out to be some of the most challenging photography I’ve done. Throughout the west we are graced with hundreds of days of bright sunshine each year. Working on the edges of daylight I’ll have to adjust something things, but normally when I head into the field the quantity of light is not usually my primary concern. While the weather in BC was unusually nice, working in the diffused light from cloud cover and the shelter of the rainforest canopy forced me to make some significant changes in my approach. To properly expose a scene and capture wildlife action I had to push my equipment and choose settings I had never used or tested.
We have three knobs to turn when making exposure choices. Aperture, shutter speed and ISO.
• Think of aperture as the throat of your camera. Aperture settings (f/stops) determine the amount of light entering the camera measured by the size of the iris or opening in the lens. Smaller aperture values (f/2.8, 4.0) are wider in diameter permitting more light. Smaller values also provide shallower depth of field (DOF). Increasing the aperture value decreases the amount of light gathered, but also increases DOF.
• Shutter speed is the amount of light entering the camera measured in time (seconds, minutes). Shutter speed also plays in when handholding or shooting off a tripod. A rough guide for handholding is the slowest possible shutter speed used should not go below the focal length of your lens. So if shooting a 200mm lens, you should shoot off a tripod if your shutter speed goes below 1/200 of a second.
Aperture and shutter speed work together in the following way. A smaller aperture, passing more light, permits higher shutter speeds with shallow DOF. This is generally what wildlife photographers are seeking. Larger apertures provide deeper DOF, but pass less light and require slower shutter speeds. This is typically a landscape photographer's formula and not a problem when shooting off a tripod.
The third variable in exposure is ISO. The rule of thumb is to use the lowest ISO setting you can. For most of the wildlife and landscape work I do locally I can get by with ISO 400 or less. When you can’t get the shutter and aperture combinations you need to make an image you have to increase ISO values to buy bandwidth.
• ISO determines the sensitivity to light of film or the sensor. Typical ISO settings range from 100 to 1600. Smaller values are less sensitive or slower, higher values are more sensitive or faster. There is also a quality component to ISO settings. Faster, or more sensitive ISO values can also introduce noise, diminishing the quality of the capture. We’ve all seen images enlarged to a point where a grain or snow effect emerges. With digital cameras this noise shows as random red or black dots and fuzziness in the image.
The bears and the environment in BC broke all my standard variables and for capturing workable images. We were shooting fast and at a variety of angles which required 90% of my shots to be handheld instead of off my tripod. This was tough when slinging long lenses. To compensate I had to get the fastest shutter speeds possible. With the soft light, DOF became a real problem for me. I could increase my aperture setting, giving me more light to work with, but not without the expense making images with too shallow of DOF. My only option was to increase ISO. I had shot very few images with my equipment above ISO 800 so I was really concerned about the quality of images I’d be taking home. I took advantage of the web to research my cameras capabilities before we hit the field. DXO Labs (dxomark.com) is an objective, independent lab that tests digital camera image capture quality. By reviewing their site, I was able to determine how my camera would perform at ISO settings well beyond anything I had shot previously.
In the end I shot most of the 6000+ images I captured at ISO 1600-2000. Having gone through these files I do have more noise than I’m accustomed to. However, it’s not beyond what I can deal with and correct on the computer. Exposure is what differentiates a good photo from a great one. So the lesson for me is broader preparation and more thoroughly ringing out a camera’s capability. I can assure you this winter I’ll be shooting a lot of test images so the next time I find myself with a new set of variables I’ll be better prepared to handle them.
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