Basic Photography Course

The polarizing filter may be thought of as a screen,

with an optical grid or slots, that stops all light that is not
vibrating in a plane parallel to the axis of the grid lines.

As the filter is rotated, the amount of polarized light

can be controlled. When the rodlike crystals are
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

transmitted.

Because polarizing filters are colorless, they can be

used as neutral density filters. Even when polarized light
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
considerably.

In color photography, the only way you can

reproduce the sky darker without affecting the other
colors in the scene is to use a polarizing filter. You can

achieve various effects from light sky to dark sky by

rotating the fiter to various positions. You can see this
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.

Getting the maximum effect with a polarizing filter

depends on your angle to the subject as well as the
rotation of the filter. When the reflection cannot be
completely eliminated, try changing your camera angle

to the subject. The maximum control of unwanted
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.

SKYLIGHT FILTERS

By absorbing ultraviolet radiation, a skylight (1A)

filter adds warmth to a scene recorded on a color

transparency film. It does this by reducing the bluish cast
prevalent in distant scenes and in scenes photographed
on heavily overcast days or in open shade. A skylight

filter is used primarily with daylight color reversal film
exposed under the above conditions. A skylight filter is
light pink in color.

FILTER FACTORS

Filters function by absorbing a portion of the light

reflected from the subject to the camera. To compensate
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

and 4, respectively. Remember, the filter factor does not
always remain constant when conditions change.

For example, a blue filter used with panchromatic

film exposed with daylight requires a smaller filter

factor than when the same film and filter are used with

tungsten light. The reason for this is daylight has a higher
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

and f/stop, more exposing light is available at the film

plane with daylight as compared to tungsten light.

A filter that absorbs a great amount of illumination

from a given light source is assigned a larger filter factor.
A filter that absorbs a lower amount of illumination from
the same light source is assigned a smaller filter factor.

To obtain the necessary light at the film plane for

correct exposure with a filter, you must increase the
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.

There are three general methods of using filter

factors to determine the exposure increase required:

1. Divide the ISO speed by the filter factor, and use

the product as the effective film speed.

Example: If the filter factor is 2 and the IS0 speed of
the film is 100, the effective film speed is 50

(100 + 2 = 50).

Thus setting a film speed of 50 on your light meter
produces the equivalent of 1 f/stop of additional
exposure.

2. Determine the required exposure without the use

of a filter; then multiply the unfiltered shutter speed by
the filter factor.

3-9

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Basic Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> The polarizing filter may be thought of as a screen, with an optical grid or slots, that stops all light that is not vibrating in a plane parallel to the axis of the grid lines. As the filter is rotated, the amount of polarized light can be controlled. When the rodlike crystals are 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 transmitted. Because polarizing filters are colorless, they can be used as neutral density filters. Even when polarized light 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 considerably. In color photography, the only way you can reproduce the sky darker without affecting the other colors in the scene is to use a polarizing filter. You can achieve various effects from light sky to dark sky by rotating the fiter to various positions. You can see this 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. Getting the maximum effect with a polarizing filter depends on your angle to the subject as well as the rotation of the filter. When the reflection cannot be completely eliminated, try changing your camera angle to the subject. The maximum control of unwanted 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. SKYLIGHT FILTERS By absorbing ultraviolet radiation, a skylight (1A) filter adds warmth to a scene recorded on a color transparency film. It does this by reducing the bluish cast prevalent in distant scenes and in scenes photographed on heavily overcast days or in open shade. A skylight filter is used primarily with daylight color reversal film exposed under the above conditions. A skylight filter is light pink in color. FILTER FACTORS Filters function by absorbing a portion of the light reflected from the subject to the camera. To compensate 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 and 4, respectively. Remember, the filter factor does not always remain constant when conditions change. For example, a blue filter used with panchromatic film exposed with daylight requires a smaller filter factor than when the same film and filter are used with tungsten light. The reason for this is daylight has a higher 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 and f/stop, more exposing light is available at the film plane with daylight as compared to tungsten light. A filter that absorbs a great amount of illumination from a given light source is assigned a larger filter factor. A filter that absorbs a lower amount of illumination from the same light source is assigned a smaller filter factor. To obtain the necessary light at the film plane for correct exposure with a filter, you must increase the 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. There are three general methods of using filter factors to determine the exposure increase required: 1. Divide the ISO speed by the filter factor, and use the product as the effective film speed. Example: If the filter factor is 2 and the IS0 speed of the film is 100, the effective film speed is 50 (100 + 2 = 50). Thus setting a film speed of 50 on your light meter produces the equivalent of 1 f/stop of additional exposure. 2. Determine the required exposure without the use of a filter; then multiply the unfiltered shutter speed by the filter factor. 3-9 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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