Another great class! We did an in-class shoot, experimenting with the trade off between aperture and shutter speed and the involvement of depth of field. Of course, that was at the end of class, so let’s start from the beginning …
Depth of field is the sense of depth or dimension in a photograph. A shallow depth of field (dof) has a selective focus, allowing the photographer to control where the viewer looks. Conversely, a deep dof makes everything, or nearly everything, in the photograph clear. The actual definition of depth of focus is “the distance range between nearest and farthest objects in a scene that remain in sharp focus. It is the area in front of and behind the point of critical focus.” So, what’s the critical focus? Your subject!
There are three factors controlling depth of field: (1) aperture/f-stop, (2) lens, and (3) distance from camera to subject.
- Aperture/f-stop … a larger aperture opening = shallow dof (ex. 2, 2.8, 4). A smaller aperture opening = greater dof (ex. 22, 16, 11). Regardless of your choice of f-stop, 1/3 in front of the subject will be sharp, while 2/3 behind your subject will be sharp.
- Lens … there are three types of lenses: normal, short and long. A standard normal lens is 50mm with the range being between 35-80mm. A standard short lens, or wide angle, is 28mm with the range being between 24-35mm. Finally, a standard long lens, or telephoto, is 200mm, with the range being between 80-500mm. So how does this translate to dof? The shorter the focal length of the lens, the greater the dof. The longer the focal length of the lens, the more shallow the dof. A shorter lens, or wide angle, increases the space between objects, while a telephoto lens decreases the space between objects. Cool, huh?
- Distance from camera to subject … The closer the camera is to the subject, the shallower the dof. The farther the camera from the subject, the greater the dof. Got it?
Now, the halving and doubling principal. As each aperture opening gets smaller, it gets smaller by half. In other words, half as much light is coming into the lens at f/5.6 than is coming through at f/4. Similarly, as each shutter speed gets smaller, the length of time the shutter stays open doubles. So 1/500 of a second is twice as long as, or double, 1/1000 of a second. That being said, apertures and shutter speeds are then reciprocally related. As each aperture opening gets smaller and less light comes in through the lens, the shutter speed must get longer to compensate.
I’ve got a question for you. You’ve got a manual control 35mm camera. You’ve traveled to a destination you’ve waited all your life to see. You pull out your camera and realize your batteries are dead and there are no stores for miles. What do you do? Thankfully, you know the sunny 16 rule. On a bright, sunny day, your f-stop will be f/16 and your shutter speed will be your film’s ISO number. Sweet, huh? If you want to change your f-stop, you simply adjust your shutter speed incrementally like this …
- f/16 = shutter speed of 125
- f/11 = shutter speed of 250
- f/8 = shutter speed of 500
- f/5.6 = shutter speed of 1000
Rock on! So what if it’s not a bright, sunny day? Here are the other starting values, which are simply stepping down (or opening up) from the sunny 16 starting point:
- partly cloudy = f/11
- bright overcast = f/8
- very overcast = f/5.6
- dreary = f/4
I think I mentioned this before, but it’s good and worth mentioning again. There are two priorities from which you can choose when composing a photograph – aperture and shutter speed. Under most circumstances, you want to set your aperture first, then your shutter speed. This allows you creative control, and isn’t that what it’s all about? The exception to this rule is for motion, in which case you’d set the shutter speed first and then determine the aperture. In that case, the motion, whether crisp or blurry, is the important element in the photograph and is your creative control.
FYI, the meter in your camera reads the quantity, not the quality, of light. Technically speaking, there are two types of meters: reflected and incident. A reflected meter is typically built into the camera and reads the light reflected off the subject. An incident meter is handheld and reads the light falling onto the subject.
Looking further at light, there are three types:
- Reflected: These are the highlights in your scene, and may include things such as the sky, blonde hair, pale skin, a wedding dress, or a white wall. In this situation, the light bounces off the bright surface.
- Absorbed: These are the shadows, and may include such things as dark hair, dark clothes, shade, or dark leaves. In this situation, the light is absorbed by the object.
- Diffused: This is very even light, and is typically cast from a fluorescent light or on an overcast day.
The general rule of exposure is …
Expose for the shadows,
develop for the highlights.
Translation … meter on the shadows, not on reflected light areas.
That’s it for this week, people. I’m OUT, and off to start my first assignment – shoot depth of field! Yeah, baby!