Equivalent Exposures and available light photography

Equivalent Exposures Film requires a certain amount of light to make a good exposure. Two factors determine the amount of light that makes the exposure: the size of the lens opening (aperture or f-stop) and the shutter speed. Set a wide aperture and you can use a fast shutter speed. Enough light will reach the film or image sensor to expose the image. But switch to a small aperture (f-stop), and you must use a slower shutter speed to get a good exposure. Many combinations of aperture (f-stop) and shutter speed produce exactly the same exposure; in other words, the same amount of light will expose the image.

If a correct exposure for a scene is 1/125 sec, the photographer can have equivalent exposure results with any of the following combinations of aperture and shutter speeds. 1/1000 1/500 1/250 1/125 1/60 1/30 1/15 F-STOP: The light entering the camera doubles with each full-stop increase in the aperture setting. SHUTTER SPEED: The light reaching the film doubles with each slower step of the shutter speed setting.

These two diagrams express the same thing.

What if you don’t have a meter,or your meter isn’t working properly? Sunny 16 Rule Almost every film packet has an exposure guide printed on it, which is based (with occasional slight variations) on the Sunny 16 rule. This tells you to set the shutter speed to the number closest to the ISO of the film. So with an ISO 400 film you set the speed to 1/400 - or rather the nearest fraction to this, 1/500. The required aperture can then be found as follows: bright sun - f16 hazy sun - f11

Following are examples of different daylight lighting conditions, some of their visual clues, and suggested aperture and shutter settings.

Bright Sunlight F-16, 125th second Visual Clues: Nothing between the subject and the sun. Bright sunlight will produce dark featureless shadows. The sun is to the back of the photographer. On snow or sand the light is affected by the strong reflections and the the photographer must be careful to take a reading from the part of the image that should show the most detail.

Hazy Sunlight F-11, 125th second

Cloudy Bright F-8, 125th second Visual Clues: Cloudy bright is a diffuse light source which will not produce shadows of the subject. The underneath side of the clouds will be white or a very light gray in color. This is an ideal light condition to photograph under as the light contrast is such it can easily be recorded on film and the subject will not be squinting or grimacing from the bright sunlight. Will give the same exposure and lighting contrast as Open Shade and Backlight

Backlight F-8, 125th second Backlight is a pleasing light direction to use as the contrast of the light matches that of the film. With backlight, the subject’s back is toward the sun and the camera is facing the direction of the sun. It is better used in a photograph during the early or later part of a bright sunlight day rather than when the sun is directly overhead. The shadow of the subject throws the frontal place into its own shadow and is similar to open shade conditions. Be careful of the lighting on the background. Select a background that is dark or in shade, or shoot down on the subject keeping sky area out of the photograph.

Open Shade is similar to both Cloudy Bright or Backlight in intensity of light striking the subject and contrast of the light. It is a pleasing light source to use but is not without its problems. The subject is in the shade of an object, but not underneath any type of overhang. Be careful of the background to make sure it is also in shade or dark. Avoid sky area. Open Shade F-8, 125th second

Deep Shade is similar to Open Shade except now the subject is underneath the object throwing the shade. The subject can be sitting in a swing on a porch or underneath a tree. The light intensity and contrast is reduced from an Open Shade condition. Watch the light intensity of the background. Avoid sky areas. Deep Shade F-5.6, 125th second

Cloudy Dark condition’s visual clues are the underneath side of the cloud is dark gray or black. No shadows are thrown by the light source. The image produced under this lighting condition can slightly lack the image contrast produced under other lighting conditions. Cloudy Dark F-5.6, 125th second

Assignment: Equivalent Exposures Make five different photos using five different f-stops. Clearly indicate in the photograph what f-stop was used to expose the image. There must be at least 20 feet of open space behind the subject. Do not shoot toward the sky.

Equivalent Exposures Exposures are taken at the same time, from the same perspective, with a medium focal length such as 50mm You will notice that the smaller the aperture, the sharper the background

Read Chapter 4 – Exposure normal exposure normal exposure underexposure underexposureoverexposure exposure meters exposure meters overriding automatic overriding automatic exposure exposure making an average exposure making an average exposure exposing light or dark scenes exposing light or dark scenes backlighting backlighting high contrast high contrast low light and reciprocity low light and reciprocity