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< Product Resources < Lighting Resources
Introduction to Lighting
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Factors Effecting Exposure
Shutter Speed
A camera’s shutter speed setting determines the time period light that is allowed to strike the film or image sensor. The shutter speed number is calibrated in fractions of a second. The larger the number, the shorter the exposure. 1 equals 1 second, 2 is ½ second, 4 is ¼ second and so on. Each increment represents half the exposure time of the previous setting.
Higher shutter speeds stop movement, whereas slower shutter speeds will cause a blurring effect when shooting fast moving subjects.
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Aperture Setting
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Shutter Setting
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F1 |
| F1.4 |
| F2 |
| F2.8 |
| F4 |
| F5.6 |
| F8 |
| F11 |
| F16 |
| F22 |
| F32 |
| F45 |
| F64 |
| F90 |
| F128 |
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1 |
| 2 |
| 4 |
| 8 |
| 16 |
| 30 |
| 60 |
| 125 |
| 250 |
| 500 |
| 1000 |
| 2000 |
| 4000 |
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F-stop
F-stops, also known as apertures, or lens openings control the amount of light passing through a lens at any given time. They are expressed as a specific size of an opening in the diaphragm (iris) of a lens in proportion to its focal length. F-stops exist in still, film, digital, and video cameras.
The higher the F number, the smaller the opening. Each consecutive higher number lets in half the amount of light of the preceding number. The lower the number, the larger the opening. Each consecutive lower number lets in twice the amount of light of the preceding number.
The lens aperture also controls depth of field. Depth of field is the distance range that appears to be in focus in front of and behind the film plane. As the aperture increases, (smaller F number), the depth of field decreases. This would be ideal if you want the subject in focus and the rest of the elements in the photograph out of focus so that the viewer’s eyes are immediately drawn to it. As the aperture decreases, (higher F number), the depth of field increases, giving you the ability to control the range of foreground and background focus.
ISO
ISO is an international standard to indicate the relative sensitivity of film to light, also called film speed. Film speed is expressed as an ISO number or an exposure index (EI). ISO ratings have replaced earlier ASA and DIN standards.
The higher the ISO number, the more sensitive or faster the film. The lower the ISO number, the less sensitive or slower the film. Film with a relatively high ISO rating requires less light for proper exposure than a lower ISO rated film.
Example: film with a speed of ISO 100 is slower than a film with a speed of ISO 200 and requires twice as much light to record the same exposure.
Many cameras automatically set the film speed by reading a code on the film cassette. Film speed must be set on exposure meters to obtain the correct exposure readings.
The ISO prefix and the older ASA speeds are numerically the same. For example, if the speed of a film were ISO (ASA) 200, you would set 200 on the ISO (ASA) dial of your camera or meter.
Exposure Meters
A good meter is essential in order to arrive at and maintain consistent exposure. Even if you choose to shoot with available light, a meter will help in controlling the detail and contrast of your images. Your exposure will be accurate, and you will save time in post-production. A bonus is consistency that adds professionalism to your work that will surely be noticed by your clients. Another advantage of using a hand held meter is the ability to achieve repeatable effects when you wish. You can choose your depth of field, lighting ratio and produce high quality results every time you record an image.
Incident Light versus Reflected Light
Light radiates from its source, whether it is the sun or an artificial source, such as an incandescent light. Light reflects off the subject and enters our eyes so that we are able to see it. The reason we see black as black and white as white is that white surfaces reflect the entire visible spectrum, whereas black surfaces absorb most of the light making it appear dark to our eyes.
Incident light is light that travels from the source to the subject and is measured before reflecting off the subject. Light reflected off the subject is called reflected light.
Most camera metering systems measure reflected light. The camera measures the light after it has already reflected off the subject. Spot meters are used at the camera position to measure small areas of light reflected off the subject.
Most handheld meters feature both incident and reflected light measurement. The advantage of an incident meter is the fact that it measures the quantity of light from the source, regardless of the tonal range of the subject.
Incident Measurement |
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Example:
Two subjects a man in a white suit, and a man in a black suit are sitting next to one another on a park bench. It’s a bright sunny day, not a cloud in the sky. The same amount of sunlight is illuminating both subjects equally; therefore the exposure should be the same for both subjects.
The reflective metering system in most cameras tries to average the exposure to an 18% (medium) gray. If you were |
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Incident Reading |
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White
Plate |
Gray
Plate |
Black
Plate |
Illustrations courtesy of Mamiya America Corp.
Sekonic Professional |
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to fill the camera frame entirely with the man wearing the black suit, the camera’s meterwill try to lighten the exposure, in order to arrive at the 18% gray value. On the other hand, if you were to fill the camera frame entirely with the man wearing the white suit, the camera’s meter will try to darken the exposure, to once again arrive at the 18% (medium) gray value. |
Even when the light source is the same, the different reflective values of blacks and whites, will cause the exposure to vary substantially with a reflective metering system, resulting in inaccurate readings.
Reflacted Measurement |
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With an incident light meter, the light source has not changed so the exposure will be exactly the same for the man in white and the man in black. The tonal values in the blacks and whites will be reproduced accurately.
If you are working with a handheld spot meter, you would have a very precise angle of light measurement as small as one degree. This gives you greater accuracy in choosing the specific tone |
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Reflacted Reading |
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White
Plate |
Gray
Plate |
Black
Plate |
Illustrations courtesy of Mamiya America Corp.
Sekonic Professional |
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| the light reflects off, to arrive at your exposure. |
Gray Card
An 18% gray card is used when you want to achieve proper exposure without having an incident meter. Since the camera’s meter is trying to arrive at an average 18% in the first place, if you fill your camera frame with the gray card in front of your subject, the camera’s meter will give you the proper exposure for this card, thereby producing an average exposure that should be quite accurate.
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