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When
an object or a section of it is centered in front of the lens,
the image it projects onto the film plane will fall in the exact
centre of the image circle. The light rays from the centered
object cross in the centre of the lens and travel an equal distance
to the film plane. This lens to subject alignment usually
provides the most accurate recording of an objects shape. |
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As
an object moves away from alignment with the centre of the
lens, or as its extremities recede from the centered position,
its projected image will move to the edges of the image circle.
Inside the camera, light rays from the farthest edges of the
object must now be projected a greater distance to the film
than the light rays projected through the centre. The
section of the object farthest from the centre of the lens
consequently expands due to the greater projection distance,
and changes the objects shape in the final image.
This
'distortion' is more noticeable with wider than normal lenses
because of the relative difference in projection distances.
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