Film making

Cinematograhy - Continuity
The Necessity of Continuity

On the set it is the responsibility of the script supervisor to see that continuity is maintained between takes and between the setups. This means that the actors must be wearing the same clothes, the same jewelry, the same hair style. If a candle or cigarette is half burned down in one take then it must be the same in all takes.

Without visual continuity a movie becomes a series of unnatural jarring moments that take the audience out of the illusion that your movie is a depiction of real life. Carefully planned lack of continuity can be an effective technique to create tension and confusion in a scene but shouldn't be overdone.

Careful notes need to be maintained. A digital camera can be a big help in maintaining continuity. Take a shot of the actors after each setup or at least at the end of the day and do a quick printout of the picture.

The script supervisor should also be marking the script with any changes in dialog that occur during filming.

The script supervisor needs to be ready to remind actors of their lines when they forget.
Focus

All cameras used in filmmaking have a lens that focuses light onto a light sensitive material. One of the most powerful techniques of cinematography involves the carefully planned use of focus.

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The lens can only bring objects at one distance from the camera into focus at a time as illustrated here:

Lens demonstration

Objects closer or farther from this point will be progressively more out of focus.

Lens demonstration

There are several variables that can be adjusted to control exactly how this looks.
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Lenses have a focal length that determines how much the image seems to be magnified. Wide angle lenses seem to make objects look smaller and farther away. Telephoto lenses seem to make objects look larger and closer. Zoom lenses have a range of focal lengths.

Because a telephoto lens magnifies the image it will make objects that are not at the focus point seem more out of focus. Wide angle lenses make it look like everything is in focus. Changes of focal length also change the perspective as you can see in these illustrations.

Lens demonstration Lens demonstration

Lenses also have a control called the aperture that controls how much light gets through the lens. The size of the opening is measured in f-stops which measure a ratio of the focal length of the lens to the size of the opening. Opening the aperture of the lens by selecting a smaller f-stop makes objects that are not at the focal plane seem more out of focus.

Lens demonstration

Closing the aperture of the lens makes all objects appear to be more in focus.

Lens demonstration

Using a telephoto lens and a large aperture gives the effect of throwing everything out of focus except for the subject the lens is focused on. This is very desirable when filming a character delivering dialog and you don't want the audience distracted by the background. Since you want the audience to pay attention to the character it is good to be able to make everything else be a bit out of focus. Compare these two images.

Lens demonstration Lens demonstration

See how the out of focus background makes the hero seem much clearer.

Filmmakers shooting on video will need to work extra hard to get this effect because the small size of the video image sensors and lens apertures compared to the large 35mm film cameras tend to make everything appear to be in focus.

Changing the size of the aperture also controls how much light gets to the light sensitive material in the camera and therefore how bright the image looks. Opening the aperture makes the image brighter and closing it make the image darker.

This is a problem if we are trying to create a purposefully out of focus background. The effect can be offset by changing the shutter speed, which is how long the light sensitive material will be exposed to light.

When the location is dark it may not be possible to change the shutter speed enough to close the lens aperture, and in bright daylight it may not be possible to open the aperture without overexposing the image. A way to get larger apertures in bright light is to use neutral density filters which are pieces of flat glass that has been dyed to be a dark gray and therefore only lets through a small amount of light.
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