vibrating in a plane parallel to the axis of the grid lines.
perpendicular to the vibration direction of the light, the
polarized light is greatly absorbed. When the rodlike
crystals are parallel to the vibration direction of the
polarized light, the polarized light is almost totally
is not present in a scene, polarizing filters can be used
to reduce the intensity of light. When two polarizing
filters are used, their combined densities can be varied
colors in the scene is to use a polarizing filter. You can
effect by viewing the scene through the viewfinder of a
single-lens reflex (SLR) camera or by viewing the scene
through the ground glass of a view camera. To see how
much reflection control you are getting, rotate the filter
as you are viewing the scene.
rotation of the filter. When the reflection cannot be
completely eliminated, try changing your camera angle
surface reflections and greatest reduction of light
intensity occurs when two polarizing filters are used
with their optical grids perpendicular to each other. This
arrangement can be either two filters in tandem in front
of the camera lens or one filter in front of the light source
and another filter in front of the camera lens. You cannot
control reflections from bare metal surfaces because the
reflected light is not polarized.
prevalent in distant scenes and in scenes photographed
on heavily overcast days or in open shade. A skylight
exposed under the above conditions. A skylight filter is
light pink in color.
for this absorption and the loss of light, you may have
to increase the exposure to compensate for the light
absorbed by the filter. A numerical value is assigned
called a "filter factor" or multiplying factor. This
numerical factor is based on several variables that
include the color sensitivity of the film, density of the
filter, color of the filter, and color temperature of the
light source. As these variables change, the filter factor
also changes to produce the correct exposure
consistently. Filters are often identified as "2 X yellow"
or "4 X orange." That implies that the filter factor is 2
always remain constant when conditions change.
content of blue light that is readily transmitted by the
blue filter. Thus, with the same film and filter
combination and with the same camera shutter speed
A filter that absorbs a lower amount of illumination from
the same light source is assigned a smaller filter factor.
original calculated exposure (without a filter). This
increase in exposure is determined with a filter factor.
When a filter has a factor greater than 1, an adjustment
to the exposure must be made.
the film is 100, the effective film speed is 50
produces the equivalent of 1 f/stop of additional
the filter factor.
Basic Photography Course