On this episode we’ll take a look at exactly how the three main areas of control work in any camera.
There are three primary areas of control in photography, each having to do with a different part of the camera: the body, the lens, and the film speed. A change to any one of these variables will necessitate a change to at least one of the other variables because the correct exposure for any given shot is actually a relationship of the three.
These principles apply to any camera that allows you to put it in manual mode and override the automatic settings. (They also apply to fully automatic cameras although you can’t control it.)
Within the camera body you can control the SHUTTER SPEED
This is how long the shutter stays open to expose the film, or in this case the digital image sensor.
- Slow shutter speeds in the half second to one second range are often used for low light conditions.
- An average shutter speed may be in the 1/60th – 1/200th of a second range.
- And a very fast shutter speed would be used for fast action sports. For example, an Indy race car speeding by might be captured at 1/2000th of a second.
The longer the shutter is open, the more light is allowed to expose the film or digital image sensor.
Within the lens you can control the APERTURE
This is a measure of how much the blades of the lens are open or closed. In a camera lens, the blades basically do the same thing as your eyes when they dilate or contract to handle different light levels.
- The lower the aperture setting, the larger the opening to allow light. The lowest setting is often referred to as shooting “wide open” because the blades don’t restrict the incoming light at all.
- Another effect aperture has on shooting is the depth of field. This is the range of the captured image that is in focus. A portrait taken with a “shallow” depth of field, for example, would have the subject in focus, while items in the background appear blurred.
- The blurry effect associated with shallow depth of field is also referred to as BOKEH.
- A portrait taken with a large depth of field will keep everything in focus.
The choice of ISO film speed affect the photo
Film speeds used in a traditional camera have an effect on the image. Film speeds have standard ISO ratings, where lower numbers refer to film associated with slower speed photography such as portraits or landscapes, and higher ISO speed films are used for fast action images.
- A high ISO film can capture an exposure much faster than a lower ISO film, but at the expense of image quality.
- Low ISO film will capture greater detail, but requires more light and/or longer exposure times to do so.
- Digital cameras have ISO equivalent settings that imitate the exact same effect achieved by film cameras.
It is possible to create similar, but not identical, effects by adjusting different variables within the lens, body or ISO. For example:
- A higher ISO film (or digital equivalent) is less sensitive to light, resulting in a darker image.
- Selecting a higher Aperture setting will allow less light to reach the sensor, resulting in a darker image.
- Shooting a faster shutter speed will expose the film or sensor for a shorter time, resulting in a darker image.
Although, each of those settings might result in the same image brightness, they also have other consequences:
- Moving to a higher ISO film (or digital equivalent) will create a “noisier” image with impacted color and more artifacts in the form of graininess.
- Selecting a higher aperture setting will have a side effect of widening the depth of field. This will bring more of the background into focus.
- Using a faster shutter speed will have the effect of freezing movement in an image. For subjects in motion this will potentially remove blur, which may at times be desirable, but at others times not so much.
Also, bokeh isn’t the blur itself. That’s just an effect of the depth of field of focus. Bokeh is the quality of the blur – how point sources of light expand and soften as they go out of focus. How even the blur is, the effect of the shape of the aperture and the lens aperture blades, how consistent the tone and brightness of the image circle is, etc.
“Good” bokeh is when a point source of light expands as a uniformly bright and tonally consistent circle of increasing size as the distance from the focus plane increases. “Bad” bokeh is when the shape diverges from a circle (cheap lenses with fewer, straight aperture blades that create pentagon/hexagon bokeh), when the circle has brighter edges than center (reflective telephoto lenses have a characteristic donut-shaped bokeh), or the color tone shifts from the center to the edge of the blurred point.
As far as depth of field – there is only one true plane of focus where everything is completely sharp. A smaller aperture simply reduces the size of the focus error (by making the light pass through a smaller hole) as distance increases from the focal plane, so elements in front of and behind the focal point still appear to be sharp. Eventually, however, even with the lens stopped down to a smaller aperture foreground and background elements will blur – depending on how close your subject is. General rule of thumb is that the “depth of field” is 1/3 in front of your focus point, and 2/3 behind it.
You got that one backwards. The higher the ISO number, the higher the light sensitivity.
John P. says
Oops, good catch, I didn’t even realize I said that. This is the kind of thing that happens when a camera is pointed in your face. 😉