324 THE HASSELBLAD MANUAL
Polarizing Filter Types
The original polarizer, known as the linear type, affects the light measuring or automatic
focusing system (or both) in some cameras to the point of giving a wrong reading or distance
setting. Whether this happens depends on the design of the metering and focusing system
in the camera. The problem has been eliminated with a polarizer known as the circular type,
which produces the same results in the picture but does not affect the metering or focusing
and can therefore be used on any camera.
The circular type is needed on Hasselblad H cameras because the main mirror has a dich-
roic coating which has a polarizing effect of its own. A linear polarizing fi lter might eliminate
the light from reaching the sensor of the automatic focusing system so circular type fi lters
must be used on H cameras. The H system polarizers are the circular type.
Circular types are not needed on the 200 cameras with a metering system nor when you
are metering with a meter prism fi nder. You can use the linear or circular type of fi lter on
these cameras. The Hasselblad polarizers for the V system cameras are the linear type.
Special Polarizing Filters
There are also special polarizing fi lters on the market that add color to refl ections and high-
lights rather than eliminating them. This addition of gold or blue or a combination of the two
can be striking; for example, in the highlights of a water surface. Like any other special effect,
it can also look unnatural and out of place. Evaluate the effect carefully before recording the
image in the camera.
THE COLOR QUALITY OF LIGHT
Color transparency fi lms are manufactured for a specifi c color or light source, and correct
color rendition can be obtained only if the color of the light matches that for which the
fi lm is balanced. The color quality of light, known as color temperature, is usually expressed
in Kelvin (K) and sometimes in Decamired (DM) values. Kelvin and Decamired values are
directly related by the following formula:
100,000
DM value
Kelvin value
Daylight color transparency fi lms used in medium-format photography are matched to a 5600
K (18 DM) value. Tungsten fi lms are matched for a 3200 K (31 DM) color temperature. Table
17-2 shows color temperatures for some light sources.
Color Quality in Digital Photography
Although the sensor in a digital camera or digital back is not made for a specifi c color temper-
ature, you still have to be concerned with the color quality of the light. To obtain the desired
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