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Created and Maintained by: The Photoimaging Information Council |
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by Russ Burden |
| July 20, 2008 | |||
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Don't just “take a picture,” “make a picture.” Take charge of the settings on your camera so the image turns out the way you want. Don’t let the camera make the decision. While the “P” mode, which actually stands for PROGRAM, provides a PERFECT exposure ninety eight percent of the time, it doesn’t know that in situation A it’s more important that the depth of field is very shallow to make your subject stand out from the background or that in situation B, it’s more important that the depth of field extends from the most foreground part of the composition and goes out to infinity. While the computers in today’s cameras are amazing and let you capture a great image, the manufacturers still haven’t figured out how to get them to interface with your brain so the final image turns out based on what you want it to look like. This being the case, it’s time to take charge of your settings to wind up with an end result of what you envisioned when you pressed the shutter. This week’s article focuses on utilizing Aperture Priority mode. See last week’s whose focus was on Shutter Priority.  © Russ Burden
Aperture Priority: The “A” setting on your camera gives priority to the aperture setting. Based on the f stop at which it’s set, given the amount of available light, the camera will choose a corresponding shutter speed to provide a good exposure. The chosen aperture will determine the amount of depth of field in the photo. The lower in value the number, for instance f 2.8 or f4, the less depth of field. The higher in value the number, for instance f16 or f22, the more depth of field. The more depth of field there is in an image, the greater the range of focus from the foreground to the background. Knowing how to control this range of focus is important when photographing subjects such as landscapes, people, animals, city scapes, and macro shots. For instance, in a landscape, the guideline is to have everything in focus from the closest point in the foreground out to the farthest point in the distance. Conversely, when photographing people, the guideline is to have the area both in front and in back of the person out of focus so the viewer’s attention is drawn just to the person.  © Russ Burden
The amount of depth of field that can be achieved is dependent upon a number of variables that must fall into place. When the lens is set to f16 or f22, the opening through which the light is passed is small. The result is not a lot of light gets to the sensor. This means the corresponding shutter speed to produce a proper exposure will be slow which often necessitates the use of a tripod. It also means that if the subject is moving or if the wind is blowing and the the subject is delicate, motion may be recorded. When all the variables fit together it’s great. When they don’t, a compromise between a desired aperture and the corresponding shutter speed must be made.  © Russ Burden
To show some real life examples of how depth of field impacts an image, study the four photos that accompany this article. In the two images of the flowers, the first was shot at f29 while the second was shot at f4.8. The focal length for both was 155mm and shot with a Nikon 5T dual element close up filter. The one shot at f29 has a much greater range of focus. The corresponding shutter speed was one eighth of a second. I had the camera mounted on a tripod and I was lucky there was no wind. The picture shot at f4.8 had a corresponding shutter speed of 1/ 250th. The difference between the two is obvious. The f29 photo provided a lot of depth of field and shows the entire flower in focus while the one shot at f4.8 produced a more artistic representation.  © Russ Burden
As I stated above, the guideline for shooting landscapes is to maximize the depth of field and for portraits to minimize it. In the landscape image of the yuccas and red rocks, everything from the foreground buds to the middle ground trees to the background rock formations are in sharp focus. The aperture at which it was shot was f22. As with the close up of the flower, the camera was on a tripod in that if I tried to hand hold the camera, the image would be soft because of the long shutter speed that was needed to get the proper exposure. In the shot of my son with the hose, I used a 200mm lens and shot the photo at f5.6. The resulting effect is throwing the background of the grass out of focus so that the only thing that’s sharp is him and the hose. If the background was in complete focus, it would compete for attention and the photo wouldn’t be as strong. The important concept to glean from all of the above is to learn how to predict the relationship between the given aperture and focal length of the lens and how it will be portrayed in your image based on how much depth of field you want. By setting your camera to aperture priority, you take charge of the end result. To learn more about this topic, join me on one of my Photographic Nature Tours. Visit www.russburdenphotography.com and click on the NATURE TOURS button for more information. Also, pick up a copy of my new book, Amphoto’s Complete Book of Photography. You can purchase a signed copy directly from me or visit your local book store or Amazon. Contact me at rburden@ecentral.com to order your signed copy.
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