Sunday, July 20, 2008

When people talk about Depth of Field (also called DOF) you may wonder why you should care as long as your pictures are in focus. Well since DOF is generally referred to as the range of over all sharpness in a photograph; and most people are instinctively drawn to the sharpest part of the photo first, I would say, it is a major player in creative control. Most articles on this subject immediately jump into talking about f-stops. These are numbers like f-1.4 or f-32 that represent how much light the aperture lets into the camera. I will explain more in a moment, but this is not where I want to start.

There are three basic things that affect Depth of Field and they are;
1) the lens aperture (f-stops)

2) the lens focal length (the size like: 35mm vs. 200mm)

3) the subject distance (how far it is from the camera)

Keep in mind that most digital cameras do not have f-stops as per say. In fact if you have a straight point and shoot camera with a set lens, it may feel like you have no control at all. Do not get discouraged. Although it does take more effort there are things you can do with any camera to enhance your DOF experience. Both the point and shoot and even many of the more advance digital cameras are based on a false premise. They assume that all people want all their photos, all the way in focus, all the time. “Now wait a minute”, you say. “I want my pictures in focus . . . don’t I?” When we say in focus, we are not talking about some 110 year old lady who can not hold the camera steady.

Here’s a photo tip that many don’t realize; depending on where you focus in any given photo; so much in front of the subject and so much behind the subject will also be in focus. Generally, more will be in focus behind the subject than in front of it. So if you really want a photo sharp from edge to edge, focus 1/3rd of the way into the scene, not dead center.

There are several really good reasons for wanting to choose a narrow DOF verses a wide DOF. Remember Wide DOF means everything in focus all the time. For those who are not quote “into” photography then this mode will satisfy their needs 90% of the time. But for the rest of us; here are some examples of when you may NOT want to shoot that way.

A) Portraits: focus on the person and blur the background. This is helpful when there are distracting elements behind the subject.

B) At the zoo: focus on only one animal. The idea here is to obscure the fact that you actually took the picture in the zoo. You want to make your photo look like you took this animal in its own natural environment.

C) Flower shots: focus on one flower or better yet even just part of a flower and let the others around it become like a painted background for your photograph.

D) Sporting Events: focus in on the one who crossed the line first, jumped the highest, or ran the fastest. You can show the winner better by using creative DOF.

Back to the basic problem, how exactly do we control Depth of Field? Shooting an object that is 5 feet from the camera will have a much smaller DOF range than shooting that same object from 25 feet away. So, regardless of what type of camera you own, move in closer!! If your camera has a zoom lens (say 35mm -200mm) the smaller the size, the wider depth of field. Most set lens are in the range of 28mm – 38mm, so there is less to adjust, less to think about, and unfortunately less control.
However, here is another photo tip you may not be aware of; if you photograph someone using the 35mm end of the scale, more of the photo will seem in focus. The opposite is also true, if you take the same photo using the 200mm length of your zoom lens, much less of the photo will appear as sharp. This is selective DOF, and it has nothing to do with f-stops. Remember that you control which part is in focus. If you do close-up photography (flowers, insects, etc) the close-focus or macro mode of your camera will already give you a fairly narrow amount of depth of field. But you can push that even further by using filters. Most cameras, will now accept filters. But even if yours does not (set lens again); you can actually hold the filter in place and shoot. Close up filters allow you to shoot much closer than the lens will by itself. They also usually narrow the depth of field and require a little more light.

Many of today’s cameras have more than one auto mode. In a fully automatic camera you have not gained much if any control, but if you have the option for Aperture priority or Shutter Priority you are back in the driver’s seat. Basically put: Aperture Priority means that you control the aperture (or f-stop) and the camera picks the right shutter speed to get a proper exposure. Conversely, Shutter Priority does the exact opposite, you control the speed and it will pick the correct aperture for the given light conditions. Since I brought it up, I guess now would be a good time to explain f-stops.
The words aperture and f-stop usually refer to the same thing. I have absolutely no idea why we don’t call them “a-stops”, but just so I don’t confuse anybody, I will call them f-stops. The f-stop controls how much light enters the camera. Many books and magazines confuse people by referring to how big the opening is and how small the depth of field is. Most people don’t care about the mechanics of the process they just want to understand the end result. A small number (like f-1.4) means only a small amount will be in sharp focus.

A large number (like f-32) means a large amount will be in sharp focus. But wait, you’re saying to yourself, “I don’t even have an aperture mode.” Maybe you do, and don’t realize it. If you’re camera has little pictures or icons on it like, many cameras do, you may have more control than you realized. The picture of the small head means portrait mode. (Your girlfriends smile will be in sharp focus but not the tree behind her.) The picture of the little mountain means landscape mode. (Your girlfriends smile will still be in sharp focus, but so will the waterfall 20 feet behind her.)

Remembering that most people are attracted to the thing that is in the sharpest focus, it becomes very hard (visually) to be attracted if the entire photo is in complete focus. There is nothing specific to draw the viewers’ attention.

By using the creative possibilities that depth of field offers; no matter what kind of camera you have, your images will be much more powerful and interesting.
Author: Tedric G.
Photographer: Michael Chee

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