Graphics Programs Reference
In-Depth Information
Telephoto lenses have longer focal lengths that magnify the image received by
the light sensor. These are used to make the subject appear closer to the pho-
tographer than it really is. Long focus lenses are often used in nature and sports
photography.
Zoom lenses have adjustable focal lengths, while prime lenses have fixed focal
lengths.
O
all lenses have
aberrations
(imperfections)
that photoshop
can help correct
(see Chapter 10,
“transforming
paths, Layers, and
Smart Objects”).
Lens Aperture
Interchangeable lenses have the ability to modulate the intensity of light strik-
ing the sensor by adjusting the size of the aperture, similar to how the pupils of
our eyes work. The f-stop ring was used in days gone by to manually adjust the
diameter of the iris diaphragm, but this is automatically driven by a motor on
modern lenses (see Figure 1.11).
Iris diaphragm
Lens aperture
F-stops follow the
geometric sequence
f/(1, 1.4, 2, 2.8, 4,
5.6, 8, 11, 16, 22),
where each succes-
sive stop has half the
light intensity of the
previous stop.
F-stop ring
FIGURe 1.11
Selecting an f-stop controls the size of the lens aperture.
The f-stop measurement is the ratio of focal length to aperture diameter. The
smaller the f-stop ratio is, the larger the aperture.
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