Why do
cameras have lenses?
A
lens is used to reconverge the rays of light reflected from an
object and focus them on a given point. This point is most usually
where the film is positioned. If we compare focusing the camera
to starting a fire with a magnifying glass, rather than concentrate
the rays of light on a single point, the rays of light through
the camera lens fan out past this point and project onto the film.
Note that because the rays of light cross over, the image of the
tree focused on the film in the diagram below is back to front
and up side down. This happens in all cameras but we don't usually
see it as it is not evident in the view finder and then it is
corrected at the printing stage.
In
the case of transparencies or slides, we view them to make visual
sense not how the camera saw them.
Move over image to view roll over image |
Move over image to view roll over image |
How
much light gets through the lens depends upon:
the aperture the lens is set at
and with auto lenses the speed of the
lens
