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All filters absorb portions of the
visible electromagnetic spectrum and pass through or transmit the
remainder. Universally, camera filters transmit light of their own
color. In some instances, they also transmit some of the light of most
immediately adjacent colors while at the same time absorbing the other
colors.
Colors that we usually see are rarely pure. Instead, they are a mixture
of two primaries. For instance, yellow is a mixture of equal parts of
red and green. If you place a green filter over your lens, it will pass
the green component reflected from a yellow subject (such as a lemon)
and block the red. Using a red filter when photographing the same lemon
will result in red being passed and green being blocked.
There are two main types of light:
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