246 THE HASSELBLAD MANUAL
camera. Lens shades must be used to eliminate all the light that falls on the lens from outside
areas and is not needed for the image. Lens shades are especially important when you are
photographing toward light sources and against white backgrounds or bright outside areas
such as overcast skies, water, and snow. A lens shade is also a good protection for the lens
when it rains or snows. I suggest keeping a lens shade on the lens at all times.
Regular square or round shades are compact and provide good shading in most cases.
They are made in different lengths to provide maximum shading for different focal length
lenses. Shades for zoom lenses must be a compromise because they can be only as long as
needed for the shortest focal length. On the Proshade in the V system and the Proshade V/H
60–95 the bellows can be extended to match the focal length of the lens. These Proshades are
highly recommended when you are photographing against white backgrounds. They can also
be used for holding gelatin or glass fi lters.
DISTORTIONS
Lens Distortion
Distortion in relation to lens design refers to the inability of the lens to record straight subject
lines as straight lines over the entire image area. Straight lines near the edges appear curved,
either inward (referred to as pincushion distortion) or outward (called barrel distortion; Figure
14-9). In some photography such as portraiture, the degree of distortion correction is less criti-
cal than in architectural, product, and scientifi c photography. Lens distortion does not change
with the lens aperture. The distortion corrections for the lenses made for Hasselblad are also
published sometimes for different distance settings. Figure 14-10 shows the distortion diagrams
for the HC 3.2/150 mm lens at infi nity and about 7 feet and Figure 14-11 shows the distortion
for the HC Macro 4/120 mm lens set at infi nity and at a distance that produces a 1:2 magnifi ca-
tion. For zoom lenses, the distortion is usually shown at different focal length settings.
Figure 14-9 Barrel or pincushion distortion. If the distortion curve has a positive value and
goes upward (left), the lens has pincushion distortion. A curve with a negative value goes
downward (right), indicating barrel distortion.
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