First 272 words of the document:
Cameras are optical instruments used to project an image of a distant mountain onto a film,
using a lens.
When you press the button it opens up the shutter to allow light to fall on the film.
These points should be considered:
CHOICE OF FILM:
A `fast' film is more sensitive to light than a `slow' film.
A `fast' film takes less time to take a photo than a `slow' film.
A `fast' film can take a photo even with a reduced amount of light.
A `fast' film can take photos of moving objects.
A `fast' film reduces quality in comparison to `slow' films.
A picture must be focused. To focus, move the lens ackwards and forwards with
the focusing screw.
For distant objects, move the lens TOWARDS the FILM: back.
For close objects, move the lens AWAY from the FILM: forward.
This controls the amount of light entering the camera.
On a dark day it could be 1/30s, on a bright day it could be 1/60s.
This refers to the diameter of the gap
An example of this is 1/8 of focal length of the lens (diameter)
This also affects the amount of light entering the camera a wider fnumber allows
more light in.
It also determines the DEPTH OF FOCUS of your photograph a small gap (e.g.
f22) will give a large depth of focus
This allows distant and close objects to be in focus.