Perspective and Scale in Landscape
Photography
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Looking at a landscape photograph, it's
not difficult to pick out which parts of the scene were close to the
camera and which farther away. Often you can even estimate with some
accuracy the approximate distances of nearby objects. Most of us take
these skills for granted, without really thinking too much about how
it's possible to look at a picture that only exists in two dimensions,
and visualize the third. It's precisely because we have so little
trouble judging depth in photographs that it's worth examining how this
discrimination is possible.
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The distances between objects in
photographs - their spatial relationships - are represented by a system
that we call perspective. The geometry of perspective is not of
interest to photographers, but some of the methods by which we infer
distance from the flat print surface can be useful in a very practical
sense. If you understand how perspective works, you can use this
knowledge to control the appearance of depth in your photographs. For
example, any photographer who owns a wide-angle lens can tell you that
such lenses give an illusion of expanded space; not all of these
photographers could tell you why, or could anticipate the circumstances
under which the illusion would be most pronounced.
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Most perspective effects work because we
know that objects in the real world stay the same size whether we are
close to them or-far away. The name that scientists give to this
experience is "size constancy". If we relied solely on the raw
information from our eyes, we'd get quite a different picture: houses
and trees would grow as we walked towards them, and people passing by
would expand and contract rather like inflating and collapsing
balloons.
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Of course this sounds ridiculous, but
it's exactly what you see on a photograph: the farther away things are,
the smaller they appear to be. For example, an avenue of poplar trees
diminishes in size in the distance, giving a vivid sensation of
receding subject planes.
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The degree of shrinking with distance is
affected by viewpoint. If you photograph the row of trees from a
considerable distance, the spaces between them are insignificant
compared to the distance between you and the avenue. The trees appear
to diminish slowly in size, and so look closer together; this effect is
called over constancy.
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To fill the frame from a distant
viewpoint you need to magnify the avenue of trees: you can do this
either by using a telephoto lens, or by greatly enlarging the negative
or transparency. It's viewpoint, though, not focal length that has
changed the perspective.
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The opposite effect occurs when you stand
at the end of the avenue, between the first two trees. The nearest
trees are vast in relation to the most distant trees, and the gaps
between them appear to close up rapidly as the avenue continues. A
wide-angle lens recreates the broad, sweeping view that you saw when
turning your head to look up and down the avenue - so these lenses
appear to expand perspective, giving a sensation of depth, or over
constancy.
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