APERTURE
[Film Technology]
[Film Technology]
For any lens, however,
the image brightness
is the same if the ratio of focal length to lens diameter is the same. This ratio is expressed as
the f/Number of the lens and is known as aperture. See also f/number.
The amount of light reaching the film is
controlled by an iris inside the lens. This
aperture is adjusted by turning a ring on the lens
barrel. Around the ring indicating the
aperture size, are stop numbers marked f5.6, f8 etc. Alternatively, the
almost identical (but more accurate) T numbers
are used, indicating the measured amount of transmitted
light actually passed by the lens. Opening up the lens to a smaller
number increases light reaching the film reduces
the depth of field. Stopping
down [stop down]to
a high number has the reverse effect. See iris, lens barrel, depth of field, stop number, t number, exposure. When focusing a zoom
lens, remember that the depth of field decreases as the angle narrows. Check focus
before shooting by zooming
into the maximum focal length (preferably at maximum aperture) focus, then zooming out and reset aperture for the take. Shapes
the exposure.
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