Photography rules (3)

part2

Depth of field
Another important thing that is needed for proper composition is called depth of field. Depth of field refers to the region of proper focus that is available in any photographic image. Usually this is not a thin region of proper focus in an image; instead, there’s some distance in front and behind the subject that will also be in focus. This entire region of sharp focus is called the depth of field, or sometimes the depth of focus.

What determines depth of field?
Three factors contribute to the depth of field.
- Aperture: The aperture of the lens is the first major factor that influences depth of field. Aperture is the size of the lens opening that determines how much light reaches the camera’s imaging sensor. Aperture is measured in f/stops, where lower f/numbers represent bigger openings and higher f/numbers are smaller openings. In addition, the smaller the aperture’s actual opening (or, in other words, the higher the f/number), the greater the depth of field will be.
- Focal length: Is just a measure of your lens’s ability to magnify a scene. The more you magnify your subject, the less depth of field you have available. When shooting with a normal or wide-angle lens, you have a lot of depth of field. If you zoom out to a telephoto magnification, your depth of field drops dramatically. Likewise, macro photography has very little depth of field as well, since you are greatly magnifying a small object.
- Subject distance: The distance from the subject determines how much depth of field you can get in your scene. If the subject is far away, the depth of field will be much greater than it is for a subject that is close to the camera. That means the region of sharp focus for a macro shot is extremely narrow, and you need to focus very, very precisely while for something very far away a vast region in front of and behind the image will be in sharp focus.

Applying depth of field in pictures
The three factors (aperture, depth of field, and subject distance) work together in any shooting situation.

“Specifically, suppose you try to take a picture with an aperture of f/5.6. At a given distance from your subject, and at a given focal length, that f/stop will yield a certain depth of field. But what happens if you change the other two factors? If you get closer to the subject, such as if you walk toward it, or if you increase the focal length by zooming in, the depth of field decreases.
So what is the point of all this? Why do you care about depth of field at all? The answer is that depth of field is an extremely important element in the overall composition of your photographs. Using depth of field, you can isolate your subject by making sure it is the only sharply focused person or object in the frame. Alternately, you can increase depth of field to make the entire image—from foreground to background—as sharp as possible. “

Using zoom lens
Zoom lens allows you to vary the focal length from a wide-angle or normal perspective all the way through some moderate telephoto length. Focal length is just a measure of the magnification that the lens provides. A larger focal length produces greater magnification; hence long focal length lenses are great for capturing fast action or enlarging objects that are moderately far away.

Important to remember is that the focal length of the given lens also affects the camera’s angle of view. Because a telephoto lens magnifies distant objects, it has a very narrow angle of view. As you reduce the magnification and zoom out toward smaller focal lengths, the angle of view likewise increases.

At the extreme end of the scale, for wide-angle lenses, the image is actually shrunk with respect to what the human eye can see. The angle of view becomes extreme, sometimes even greater than 180 degrees. This kind of wide-angle lens is known as a fish-eye lens due to the peculiar effect of the angle of view.
The focal length of your lens has one other important characteristic. Depending upon whether you have your lens set to wide angle, normal, or telephoto, you’ll get a very different depth of field. A telephoto setting yields minimal depth of field, while a wide-angle setting generates a lot of focusing depth.

Maximizing depth of field
The three ways to maximize the depth of field in your image are:
- Use a lens with a short focal length, such as the normal or wide-angle setting on your camera’s zoom.
- Focus on a distant subject. If you’re trying to get both a nearby tree and a more distant house in focus simultaneously, for instance, focusing on the house, rather than the tree, is more likely to deliver both subjects in focus.
- Use the smallest aperture you can, such as f/11 or f/16.
Not surprisingly, you can minimize the depth of field in a picture by doing exactly the opposite of these things.

to be continued

part 2