UtahWest Photographics - Basic Photography Course

UtahWest Photographic's Free Basic Photography Series

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Film and Helpful Tables

Film is a strip or sheet of light sensitive material which must be exposed to light to make an image. No matter what kind of lighting you are taking photographs in, the film exposure must be at the proper level to yield acceptable results in the finished photograph. All film has an exposure rating which is called the ISO. The ISO indicates how much time a certain amount of light must reach the film for it to be properly exposed. The amount of light and the time that light is allowed to reach the film determine how much exposure the film gets. If too

Photo 5.1 A typical dial on a hand held light meter. The dial above shows the many combinations of shutter speed and aperture which can be used to give the same exposure.

much light is allowed to reach the film, the light is allowed to reach the film too long or both occur, the film is said to be overexposed. The negative will be dark and the print will be too light. If not enough light reaches the film, the light doesn't reach the film long enough or both occur, the film is said to be underexposed. The negatives will be thin and light and the print will be too dark.

REMEMBER: Proper exposure is determined by the amount of time (controlled by shutter speed) and the intensity and amount of light (controlled by aperture) that is allowed to reach the film.

LIGHT INTENSITY X TIME = EXPOSURE

Automatic cameras use a built in light meter to determine exposure and automatically set the shutter speed and aperture accordingly. With manual cameras and exposure meters, a meter reading is taken of a scene and a shutter speed and aperture are indicated for the proper exposure of the film being used. The photographer then adjusts the settings to get the proper exposure.

This can be more easily understood by thinking of a bucket of water. Let's say you need to put exactly one gallon of water into a bucket. The gallon would represent the ISO rating of the film you use. The size of the steam of water going into the bucket will represent the aperture of the lens you are using. The amount of time it takes you to fill the bucket to exactly one gallon represents the shutter speed you use on your camera. If you use a large stream of water (a wide aperture on your camera) it will take less time (slower shutter speed) to fill the bucket (make the proper exposure). If you let the water trickle into the bucket, it will take much longer to get the gallon of water into the bucket. This is like using a small aperture with a longer shutter speed.

Photo 5.2 Over and underexposure dials are available on some automatic exposure cameras.

Once the scene of a photograph is metered and the proper exposure is determined, the photographer, using a manual camera or an automatic camera with selective exposure, can choose to let the shutter speed determine the aperture or he can allow the aperture to control the shutter speed. For example, imagine you take a meter reading of a scene and you want to use a fast shutter speed of 1/125th of a second. The meter will tell you what aperture to use for that shutter speed. Likewise, if you need to use a certain aperture, you can set that aperture and then set the shutter speed according to it. Let's say you are photographing a marathon and you want to use a shutter speed of 1/125th a second so that the runners are not blurry in your photographs. You set your light meter to 1/125th of a second and then meter the scene to determine what aperture is necessary to expose the film you have chosen to use. Let's assume at 1/125th of a second, your film choice calls for an aperture of f:8. So our exposure for this film is 1/125th of a second at f:8. You can double your shutter speed to 1/250th of a second and still maintain the proper exposure by opening up the aperture on your camera to f:5.6. What you have done here is shortened the amount of time the light reaches the film by half but you have doubled the amount of light reaching the film. This maintains the proper exposure.

On a camera, the shutter speeds are either doubled or halved, depending on which way you go on the scale. So 1/60th of a second is twice as fast as 1/30th of a second and it is one half as fast as 1/125th of a second. Apertures are also used the same way. An aperture of f:5.6 will let in twice as much light as an aperture of f:8 and half as much as an aperture of f:4. This is called the "law of reciprocity". The law of reciprocity says that if you determine the proper exposure for a scene and then change the shutter speed or aperture, you must change the other to maintain the proper exposure. The two following camera settings will give the same exposure to film when exposed to the same scene:

EXPOSURE 1: 1/500th of a second at f:4

EXPOSURE 2: 1/125th of a second at f:5.6

Photo 5.3 The ISO dial on your camera can be used to manipulate exposures when there is no other control to do so.

In Example #1, a shutter speed/aperture combination are used to give the proper exposure to the film you are using. This is determined by taking a meter reading of the subject you are photographing. In Exposure #2, the time the light is allowed to reach the film is doubled. Using the reciprocity effect, the photographer must cut the light in half to maintain the proper exposure level. This is done by changing the camera aperture to f:5.6, which allows exactly half the light of f:4 to reach the film during exposure. Using this principal, many different combinations of f:stops and shutter speeds can be used to make photographs with the proper exposure level. After determining exposure, changing only one of the exposure settings (shutter speed or f:stop) will give over or under exposed negatives and prints.

At times, you may want to deliberately overexpose or underexpose a photograph. This is easily done by changing the exposure settings on your camera as needed. If you do not have manual exposure adjustments you can change the film speed dial to change the exposure. A film with an ISO rating of 400 requires exactly half as much light as does a film with an ISO rating of 200. By changing the film speed dial on your camera to 200, when shooting ISO 400 film, your film will be one stop overexposed. By changing the setting to 800, it will be one stop underexposed. This would be the same as changing the f:stop or shutter speed by one setting. Some cameras an over/underexposure dial. This allows you to dial in +1, +2, -1 or -2 stops of exposure. This is very essential at times. A good example of needing to change the exposure is when you photograph a subject in front of a large backlight, like a sunset. Using the exposure meter, the subject in front of the backlight will be a silhouette. Overexposing your film by two stops (twice as much light) will bring out detail in the subject in the foreground but will wash out and make brighter, the backlight. Underexposure can be used in theaters where a subject is under a bright spotlight surrounded by large dark areas. A normal meter reading would leave the subject very light and washed out in the photograph. By underexposing two stops (1/4th as much light) the subject will be exposed correctly but the dark areas will become very dark.

Types of Film

If you have been to the local camera store, you have seen all the different kinds of films and their different film speeds. It can be very confusing when trying to determine what kind of film you need. There are basically four different kinds of film available.

Color Negative Film

This is the most widely used film. When the film is developed it has a negative image on it. This negative image is then printed onto a "negative" paper, giving the positive image you see in your photographs. Negatives can be stored for a long period of time if they are stored properly. Reprints can easily be made at anytime from these negatives.

Color Transparency Film

When this film is developed, a positive image is made. For the most part, each individual frame is cut out and placed into a "slide mount". Then these images are viewed using a backlight, usually using a slide projector. The disadvantage to this type of film is that there is no negative to store and it is more expensive to have prints made from "slides".

Black and White Negative Film

The same as color negative film but a black and white image is made from the negative rather than a color image. Color prints cannot be made from a black and white negative.

Black and White Transparency Film

The same as color transparency film but the image is in black and white. Normally a black and white negative film is used but a different development method is used to make the transparency instead of a negative.

Film Speeds

Film comes in various speeds. The ISO rating of film guides you in setting the exposure properly as we have discussed. The lower the ISO number, the more light is required to expose the film. Higher speed films require less light to be properly exposed but they do not yield prints with as high quality as slower films due to the grain being larger in the faster films. If you take photographs mainly outdoors, in bright sunlight, a slow to moderate speed film, 25, 50, 64, or 100 ISO would be the best choice to give the best quality photographs. If you shoot mostly indoors, without a flash, a higher speed film, 400, 800, 1000 or 1600, would be the obvious choice although the quality of the print would suffer somewhat.

Film Choice

Slow Films	Moderate Speed Films	Fast Films
25, 50, 64	100, 125, 160, 200	400, 1000, 1600 and up

Each person must determine what their needs are when they photograph and pick the film they feel best suits their needs. Let me encourage you to try different kinds and speeds of film to learn how they react differently.

What Kind of Film to Use

Activity	Film Choice
Outdoors in bright sunlight	Slow
High degree of enlargement or quality needed	Slow
Outdoors with bright or cloudy light	Moderate
Indoors with flash	Moderate
Night shots with long exposures	Moderate
Indoors with dim lighting	Fast
Fast action with high shutter speeds	Fast
Indoor or night time sports	Fast

Differences Between the Human Eye and The Camera and Film

The Human Eye	The Camera and Film
Sees only three dimensionally	Cannot see depth, only height and width
Sees only a "normal" image	Has interchangeable lenses that produce different image sizes, relationships
Cannot slow action	Has a shutter to stop action or to allow blur
Can see in only one size	Through different lenses, various magnifications are possible
Is selective, seeing only what it chooses to see	Is objective, records everything the film speed allows
Is sensitive to color and sees color normally	May altar the coloration or translate color into shades of gray
Cannot store light	Through time exposure, may record images not able to be seen with the eye
Is sensitive only to the visible spectrum of light	With special films can also see infrared, ultraviolet, x-ray
Cannot retain or combine a number of images	Can double exposure or produce special effects with filters and masking
Accepts apparent convergence of parallel lines	Produces convergence but can be annoying when compared to frame edges. Can be connected with some cameras and in the enlarger

Depth of Field Suggestions

For Maximum Depth of Field	For Minimum Depth of Field
Stop down the lens (smaller aperture, larger f:number)	Open up the lens (larger aperture, smaller f:number)
Move back from the subject	Move closer to the subject
Change to a wide angle lens	Change to a telephoto lens
Focus one-third of the way into the scene	Focus on the front of the subject
Check depth of field scale or depth of field previewer	Check depth of field scale or depth previewer