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Introduction
| Camera Filters for Color and Black and White
Special Effect Filters | Filters for
Black and White
Filters for Color | Special Application
Filters
Other Filter Considerations
INTRODUCTION
TO FILTERS
Filter
Planning | Filter
Factors | Filter
Grades | Back to top
Camera filters are transparent
or translucent optical elements that alter the properties of light entering
the camera lens for the purpose of improving the image being recorded. Filters
can affect contrast, sharpness, highlight flare, color, and light intensity,
either individually, or in various combinations. They can also create a variety
of "special effects." It is important to recognize that, even though there are
many possibly confusing variations and applications, all filters behave in a
reasonably predictable way when their properties are understood and experienced.
Most of these properties related similarly to filter use in both film and video
imaging. The following will explain the basic optical characteristics of Tiffen
and certain other types of camera filters, as well as their applications. It
is a foundation upon which to build by experience. Textual data cannot fully
inform. There is always something new out there.
In their most successful
applications, filter effects blend in with the rest of the image to help get
the message across. Use caution when using a filter in a way that draws attention
to itself as an effect. Combined with all the other elements of image-making,
filters make visual statements, manipulate emotions and thought, and make believable
what otherwise would not be. They get the viewer involved. Back
to top
Filter
Planning
Filter effects can become a key part of the "look" of a production, if considered
in the planning stages. They can also provide a crucial last-minute fix to unexpected
problems, if you have them readily available. Where possible, it is best to
run advance tests for pre-conceived situations when time allows. Back
to begining
Filter
Factors
Colored and polarizing filters reduce the amount of light transmitted to the
film, and so require some exposure compensation. Built-in TTL metering will
handle this to a degree, but for greatest accuracy, it's best to take a meter
reading without the filter, open the lens the required amount, then attach the
filter and shoot.
See the filter instruction
sheet for the factor for your filter(s)How do you know how much to increase
exposure for a given filter? By its filter factor. The manufacturer provides
a filter factor for each filter that requires exposure compensation. The filter
factor tells you how much you must increase exposure when using that filter.
A filter factor of 2 means you have to double the exposure (i.e., open the lens
one stop); a filter factor of 4 means you have to increase the exposure 4X (open
the lens two stops).
When in doubt in the field
about compensation needed for a filter that you have no information on, you
might use your light meter with the incident bulb removed. If you have a flat
diffuser, use it, otherwise just leave the sensor bare. Aim it at an unchanging
light source of sufficient intensity. On the ground, face up at a blank sky
can be a good field situation. Make a reading without the filter. Watch out
for your own shadow. Make a reading with the filter covering the entire sensor.
No light should enter from the sides. The difference in the readings is the
compensation needed for that filter. You could also use a spot meter, reading
the same bright patch, with similar results. There are some exceptions to this
depending on the filter color, the meter sensitivity, and the target color,
but this is often better than taking a guess. Back to begining
Filter
Grades
Many filter types are available in a range of "grades" of differing strengths.
This allows the extent of the effect to be tailored to suit various situations.
The grade numbering range can vary with the effect type, and generally, the
higher the number, the stronger the effect. Unless otherwise stated, there is
no mathematical relationship between the numbers and the strengths. A grade
4 is not twice the strength of a grade 2. A grade 1 plus a grade 4 doesn't add
up to a grade 5. Back to begining
CAMERA
FILTERS FOR BOTH COLOR AND BLACK-AND-WHITE
Ultraviolet
Filters | Infra-Red Filters | Neutral
Density Filters
Color-Grad® Gradated ND Filters | Polarizing
Filters | Back to top
Ultraviolet
Filters
Film, as well as video, often exhibits a greater sensitivity to what is to us
invisible, ultraviolet light. This is most often outdoors, especially at high
altitudes, where the UV-absorbing atmosphere is thinner; and over long distances,
such as marine scenes. It can show up as a bluish color cast with color film,
or it can cause a low-contrast haze that diminishes details, especially when
viewing far-away objects, in either color or black-and-white. Ultraviolet filters
absorb UV light generally without affecting light in the visible region.
It is important to distinguish
between UV-generated haze and that of air-borne particles, such as smog. The
latter is made up of opaque matter that absorbs visible light as well as UV,
and will not be appreciably removed by a UV filter.
Ultraviolet filters come
in a variety of absorption levels, usually measured by their percent transmission
at 400 nanometers (nm), the visible-UV wavelength boundary. Use a filter that
transmits zero percent at 400 nm, such as the Tiffen Haze 2, for aerial and
far-distant scenes; the Tiffen Haze 1, transmitting 29% at 400 nm, is fine for
average situations. Back to begining
Infra-Red
Filters
Certain special situations call for the use of black-and-white or color infra-red
sensitive films. For aerial haze penetration, recording heat effects, and other
purposes they are invaluable. Their color and tonal renditions are very different,
however, from other film types (consult film manufacturers for further details).
Various filters are used to reduce unwanted visible light. Red, orange, and
yellow filters, as used for panchromatic black-and-white film can enhance contrast
and alter color. Total visible light absorption transmitting only infra-red,
as with the Wratten #87 or #89 series of filters, can also be useful. The results
will vary with film type and other factors. Prior testing for most situations
is a must. Back to begining
Neutral
Density Filters
When it is desirable to maintain a particular lens opening for sharpness or
depth-of-field purposes, or simply to obtain proper exposure when confronted
with too much light intensity, use a neutral density (ND) filter. This will
absorb light evenly throughout the visible spectrum, effectively altering exposure
without requiring a change in lens opening and without introducing a color shift.
Neutral density filters
are denoted by (Optical) Density value. Density is defined as the log, to base
10, of the Opacitance. Opacitance (degree of absorption) of a filter is the
reciprocal of (and inversely proportional to) its Transmittance. As an example,
a filter with a compensation of one stop has a Transmittance of 50%, or 0.5
times the original light intensity. The reciprocal of the Transmittance, 0.5,
is 2. The log, base 10, of 2 is approximately 0.3, which is the nominal density
value. The benefit of using density values is that they can be added when combined.
Thus two ND .3 filters have a density value of 0.6. However, their combined
transmittance would be found by multiplying 0.5 x 0.5 = 0.25, or 25% of the
original light intensity.
Neutral density filters
are also available in combination with other filters. Since it is preferable
to minimize the number of filters used (see section on multiple filters), common
combinations such as a Wratten 85 (daylight conversion filter for tungsten film)
with a ND filter are available as one filter, as in the 85N6. In this case,
the two stop ND .6 value is in addition to the exposure compensation needed
for the base 85 filter. Back to begining
Color-Grad®
Gradated ND Filters
Often it is necessary or desirable to balance light intensity in one part of
a scene with another, in situations where you don't have total light control,
as in bright exteriors. Exposing for the foreground will produce a washed-out,
over-exposed sky. Exposing for the sky will leave the foreground dark, under-exposed.
Color-Grad ND filters are
part clear, part neutral density, with a smoothly graded transition between.
This allows the transition to be blended into the scene, often imperceptibly.
A ND .6-to-clear, with a two stop differential, will most often compensate the
average bright sky-to-foreground situation.
These filters are also available
in combination colors, as where the entire filter is, for example a Wratten
85, while one half also combines a graded-transition neutral density, as in
the 85-to-85N6. This allows the one filter to replace the need for two.
Color-Grad filters generally
come in three transition types. The most commonly used is the "soft" gradation.
It has a wide enough transition area on the filter to blend smoothly into most
scenes, even with a wide angle lens (which tends to narrow the transition within
the image). A long focal length, however, might only image in the center of
the transition. In this case, or where the blend must take place in a narrow,
straight area, use a "hard" gradation. This is ideal for featureless marine
horizons. For situations where an extremely gradual blend is required, an "attenuator"
is used. It changes density almost throughout its length.
The key to getting best
results with a Color-Grad filter is to help the effect blend in as naturally
as possible. Keep it close to the lens, to maximize transition softness. Avoid
having objects in the image that extend across the transition in a way that
would highlight the existence of the filter. Don't move the camera unless the
transition can be maintained in proper alignment with the image throughout the
move. Make all positioning judgments through a reflex viewfinder at the actual
shooting aperture, as the apparent width of the gradation is affected by a change
in aperture.
Color-Grad filters are best
used in a square, or rectangular format, in a rotating, slidable position in
a matte box. This will allow proper location of the transition within the image.
They can be used in tandem, for example, with one affecting the upper half,
the second affecting the lower half of the image. The center area can also be
allowed to overlap, creating a stripe of the combination of effects in the middle,
most effectively with gradated filers in colors (see section on "Color-Grad
Gradated Color Filters). Back to begining
Polarizing
Filters
Polarizes allow color and contrast enhancement, as well as reflection control,
using optical principles different from any other filter types. Most light that
we record is reflected light that takes on its color and intensity from the
objects we are looking at. White light, as from the sun, reflecting off a blue
object, appears blue because all other colors are absorbed by that object. A
small portion of the reflected light bounces off the object without being absorbed
and colored, retaining the original (often white) color of its source. With
sufficient light intensity, such as outdoor sunlight, this reflected "glare"
has the effect of washing out the color saturation of the object. It happens
that, for many surfaces, the reflected glare we don't want is polarized while
the colored reflection we do want isn't.
The waveform description
of light defines non-polarized light as vibrating in a full 3601 range of directions
around its travel path. Polarized light is defined as vibrating in only one
such direction. A polarizing filter passes light through in only one vibratory
direction. It is generally used in a rotating mount to allow for alignment as
needed. In our example above, if it is aligned perpendicularly to the plane
of vibration of the polarized reflected glare, the glare will be absorbed. The
rest of the light, the true-colored reflection, vibrating in all directions,
will pass through no matter how the polarizing filter is turned. The result
is that colors will be more strongly saturated, or darker. This effect varies
as you rotate the polarizer through a quarter-turn, producing the complete variation
of effect, from full to none.
Polarizers are most useful
for increasing general outdoor color saturation and contrast. Polarizers can
darken a blue sky, a key application, on color as well as on black-and-white
film, but there are several factors to remember when doing this. To deepen a
blue sky, it must be blue to start with, not white or hazy. Polarization is
also angle-dependent. A blue sky will not be equally affected in all directions.
The areas of deepest blue are determined by the following "rule of thumb." When
setting up an exterior shot, make a right angle between thumb and forefinger.
Point your forefinger at the sun. The area of deepest blue will be the band
outlined by your thumb as it rotates around the pointing axis of your forefinger,
directing the thumb from horizon to horizon. Generally, as you aim your camera
either more into or away from the sun, the effect will gradually diminish. There
is no effect directly at or away from the sun. Do not pan with a polarizer,
without checking to see that the change in camera angle doesn't create undesirable
noticeable changes in color or saturation. Also, with an extra-wide-angle view,
the area of deepest blue may appear as a distinctly darker band in the sky.
Both situations are best avoided. In all cases, the effect of the polarizer
will be visible when viewing through it.
Polarizers need approximately
1-1/2 to 2 stops exposure compensation, without regard to rotational orientation
or subject matter. They are also available in combination with certain standard
conversion filters, such as the 85BPOL. In this case, add the Polarizers compensation
to that of the second filter.
Certain camera optical systems
employ internal surfaces that themselves polarize light. Using a standard (linear)
polarizer will cause the light to be further absorbed by the internal optics,
depending on the relative orientation. A Circular Polarizer is a linear one
to which has been added, on the side facing the camera, a quarter wave "retarder."
This "corkscrews" the plane of polarization, effectively depolarizing it, eliminating
the problem. The Circular Polarizer otherwise functions in the same manner.
Polarizers can also control
unwanted reflections from surfaces such as glass and water. For best results,
be at an angle of 32 to 34 degrees incident to the reflecting surface. Viewing
through while rotating the polarizer will show the effect. It may not always
be advisable to remove all reflections. Leaving some minimal reflection will
preserve a sense of context to a close-up image through the reflecting surface.
A close-up of a frog in water will appear as a frog out of water without some
tell-tale reflections.
For relatively close imaging
of documents, pictures, and small three-dimensional objects, in a lighting-controlled
environment, as on a copy stand, plastic Polarizers mounted on lights aimed
at 45 degrees to the subject from both sides of the camera will maximize the
glare-reducing efficiency of a polarizer on the camera lens. The camera, in
this case, is aimed straight at the subject surface, not at an angle. The lighting
Polarizers should both be in the same, perpendicular orientation to the one
on the lens. Again, you can judge the effect through the polarizer. Back
to begining
SPECIAL
EFFECT FILTERS
General
Information | Diffusion
Filters | Sliding
Diffusion Filters
Fog, Double
Fog and Pro-Mist® | Contrast Control Filters
Star Effect Filters | Back to top
General
Information
The following filter types are available in a wide range of grades useful in
both color and black-and-white imaging. They have no recommended filter factors,
but may require exposure compensation based on several things. Filters that
lower contrast or create flare, where contrast and/or light intensity is higher,
will do more for any given grade. Working with light, the more they have, the
more they can do. The same filter, in two different lighting conditions, may
produce two different effects. With diffusion, or image softening filters, higher
contrast scenes appear sharper, needing more diffusion, than scenes of lower
contrast. Diffusion requirements will also vary with other conditions. Smaller
film formats will allow less diffusion, as will large-screen projection. Color
may allow less diffusion than black and white. Producing for television may
require a greater degree of diffusion to survive the transition. These relationships
should cause you to choose exposure and filter grade based on the situation
and personal experience. Prior testing is always recommended, when possible.
Back to begining
Diffusion
Filters
Many different techniques have been developed to diffuse image-forming light.
Stronger versions can blur reality for a dream-like effect. In more subtle forms,
diffusion can soften wrinkles to remove years from a face. The optical effects
all involve bending a percentage of the image-forming light from its original
path to defocus it.
Some of the earliest "portrait"
diffusion filters still in use today are "nets." Fine mesh, like a stocking,
stretched across the lens, has made many a face appear youthful, flawless. More
recently, these can be obtained as standard-sized optical glass filters, the
Tiffen Softnet® series. These function through "selective diffusion." They have
a greater effect on small details, such as wrinkles and skin blemishes, than
on the rest of the image. The clear spaces in the mesh transmit light unchanged,
preserving the overall sharp appearance of the image. Light striking the flat
surface of the net lines, however, is reflected or absorbed. A light-colored
mesh will reflect enough to tint shadows, either lighter, which lowers contrast,
or also adding its color, while leaving highlight areas alone. The effect of
diffusion, however, is produced by the refraction of light that just strikes
the edges of the mesh lines. This is bent at a different angle, changing its
distance to the film plane, putting it out of focus. It happens that this has
a proportionately greater effect on finer details than on larger image elements.
The result is that fewer wrinkles or blemishes are visible on a face that otherwise
retains an overall, relatively sharp appearance.
The finer the mesh, the
more the image area covered by mesh lines, and the greater the effect. Sometimes,
multiple filters are used to produce even stronger results.
As with any filter that
has a discrete pattern, be sure that depth of-field doesn't cause the net filter
lines to become visible in the image. Using small apertures, or short focal
length lenses make this more likely, as will using a smaller film format, such
as 16mm vs. 35mm, given an equal field of view. Generally, mid-range or larger
apertures are suitable, but test before critical situations.
When diffusing to improve
an actor's facial appearance, it is important not to draw attention to the presence
of the filter, especially with stronger grades, when diffusion is not required
elsewhere. It may be desirable to lightly diffuse adjacent scenes or subjects,
not otherwise needing it, to ensure that the stronger filtration, where needed,
is not made obvious.
In diffusing faces, it is
especially important that the eyes do not get overly soft and dull. This is
the theory behind what might be called circular diffusion filters. A series
of concentric circles, sometimes also having additional radial lines, are etched
or cast into the surface of a clear filter. These patterns have the effect of
selectively bending light in a somewhat more efficient way than nets, but in
a more radial orientation. This requires that the center of the circular pattern
is aligned with one of the subject's eyes, not always an easy, or possible,
task, to keep it sharp. The rest of the image will exhibit the diffusion effect.
A variation on the clear-center
concept is the Center-Spot filter. This is a special application filter that
has a moderate degree of diffusion surrounding a clear central area that is
generally larger than that of the circular diffusion filter mentioned previously.
Use it to help isolate the main subject, held sharp in the clear center. while
diffusing a distracting background, especially in situations where a long lens
and depth-of-field differentiation aren't possible.
Another portrait diffusion
type involves the use of small "dimples," or clear refracting shapes dispersed
on an otherwise clear optical surface. They can be round or diamond-shaped.
These are capable of more efficient selective diffusion than the net type, and
have no requirement to be aligned with the subject's eye. They don't lower contrast,
as by tinting shadows, as light-colored nets do. These dimples refract light
throughout their surface, not just at the edges. For any given amount of clear
space through the filter, which is relative to overall sharpness, they can more
efficiently hide fine details than net filters. A more recent development, the
Tiffen Soft/FX® series involves a minutely detailed series of patterns, made
up of tiny "lenslets," each with a greater degree of curvature, with more optical
power, than that developed by the dimples previously mentioned. This produces
a maximum of selective diffusion efficiency for any given amount of overall
sharpness.
The above types of filters,
though most often used for "portrait" applications, also find uses wherever
general sharpness is too great, and must be subtly altered. Back
to begining
Sliding
Diffusion Filters
When attempting to fine-tune the application of diffusion within a sequence,
it can be invaluable to be able to vary the strength of the effect while filming.
This can be accomplished by employing an oversized filter that has a gradated
diffusion effect throughout its length. It is mounted to allow sliding the proper
grade area in front of the lens, which can be changed "on-camera." When even
more subtle changes are required, maintaining consistent diffusion throughout
the image while varying the overall strength, a dual "opposing gradient" filter
arrangement can be used. Back to begining
Fog,
Double Fog and Pro-Mist®
A natural fog causes lights to glow and flare. Contrast is generally lower,
and sharpness may be affected as well. Fog filters mimic this effect of atomized
water droplets in the air. The soft glow can be used to make lighting more visible,
make it better felt by the viewer. The effect of humidity in, say, a tropical
scene can be created or enhanced. In lighter grades, these filters can take
the edge off excess contrast and sharpness. Heavier grades can create unnatural
effects, as for fantasy sequences. In general, however, the effect of a strong
natural fog is not produced accurately by Fog filters in their stronger grades
That is because they are too fuzzy, with too much contrast, to faithfully reproduce
the effect of a thick natural fog. For that, Double Fog filters are recommended.
Double Fog filters have
milder flare and softening characteristics than standard Fog filters while exhibiting
a much greater effect on contrast, especially in the stronger grades. A very
thick natural fog will still allow close-up objects to appear sharp. So will
a Double Fog filter. They key to the effect is the much lower contrast combined
with a minimal amount of highlight flare.
Pro-Mist filters generally
produce highlight flare that, by staying closer to the source, appears more
as a "halo" than will the more outwardly extended flare of a fog filter. They
create an almost pearlescent glow to highlights. The lighter grades also find
uses in toning down the excessive sharpness and contrast of modern film and
lens combinations without detracting from the image. Black Pro-Mist filters
also create moderate image softening and modest-to-strong highlight flare, but
without as much of a lightening effect on shadows. Back to
begining
Contrast
Control Filters
There are many situations, such as bright sunlit exteriors, where proper contrast
is difficult to maintain. Exposing for either highlights or shadows will leave
the other severely under or over exposed. Tiffen Low Contrast filters create
a small amount of "localized" flare near highlight areas within the image. This
reduces contrast by lightening nearby shadow areas, leaving highlights almost
unchanged. Tiffen Soft Contrast filters include a light absorbing element in
the filter which, without exposure compensation, will reduce contrast by also
darkening highlights. Use this latter filter when lighter shadows are not desired.
In both cases, the mild flare produced from bright highlights is sometimes used
as a lighting effect.
Another, more recently developed
type of filter reduces contrast without any localized flare. The Tiffen Ultra
Contrast filter series uses the surrounding ambient light, not just light in
the image area, to evenly lighten shadows throughout. Use it where contrast
control is needed without any other effect on sharpness or highlight flare being
apparent. Back to begining
Star
Effect Filters
Lighting can be enhanced in ways that go beyond what exists in nature. Star
filters create points of light, like "stars," streaking outward from a central
light source. This can make lighting within the scene take on a more glittering,
glamorous appearance. This effect is produced by a series of thin lines etched
into the flat optical surface of a clear filter. These lines act as cylindrical
lenses, diffracting light points into long thin lines of light running perpendicular
to the etched lines. Lines on the filter positioned horizontally produce vertically
oriented star lines.
The size and brightness
of the star lines produced are first a function of the size, shape, and brightness
of the light source. You have additional control through the choice of a particular
spacing between the lines on the filter. Generally these spacing are measured
in millimeters. A 1mm spacing has twice as many lines per unit area as a 2mm
spacing. It will produce a brighter star for any given source. Spacing offered
generally range from 1mm to 4mm, as well as both narrower and wider for specialty
effects.
The number of directions
that lines run in determines the number of points produced. Lines in one direction
produce a two-pointed star, just a streak through the center of the light. There
are 4, 6, 8, 12 and more points available. With an 8 or 12 point filter, the
many star lines will tend to overpower the rest of the image, so use them carefully.
Although the more common types have a symmetrical arrangement of points, they
can also be obtained with asymmetric patterns, which tend to appear more "natural,"
less synthetic. Examples of these latter types are the Tiffen Vector-, Hyper-,
North-, and Hollywood Star filters.
As with any filter that
has a discrete pattern, be sure that depth of field doesn't cause the filter
lines to become visible in the image. Using small apertures, or short focal
length lenses make this more likely, as will suing a smaller film format, such
as 16mm vs. 35mm given an equal field of view. Generally, mid-range apertures
or larger are sufficient, but test before critical situations. Back
to begining
FILTERS
FOR BLACK AND WHITE
Tone
Control Filters | Back to top
Tone
Control Filters
Black and white imaging records only tonal differences between colored objects,
which appear as black, white, or different shades of gray. Proper rendition
depends on your own desires, and, for film, the differences between film sensitivity
to colors and that of the eye. The latter is due to the fact that most panchromatic
emulsions used are more sensitive to blue, violet and ultraviolet than to other
colors. Therefore, blue appears as lighter on film than it does to the eye.
This can make a blue sky light enough to appear a similar shade of light gray
as the clouds that are in it, making the clouds "disappear." A more "correct"
cloud presence is obtained through the use of a yellow filter, such as a Wratten
#8, which can absorb blue light, darkening the sky to more closely match what
the eye would see. The #8 also acts as a general compensator for most subjects,
giving a tonal rendition similar to that of the eye. Deeper colors, further
to the red end of the spectrum, such as Wratten #15 deep yellow, #16 orange,
and #25 and #29 red filters will produce progressively deeper and artificially
more dramatic renditions of blue sky.
Remember that, since these
filters act on color differences to produce tonal differences, the required
colors must be present. The part of the sky you are recording must be blue to
be affected. Sky sections closer to the sun, or nearer the horizon, are generally
less blue than elsewhere. Use of a gradated neutral density filter can darken
a sky relative to the foreground, but will not increase contrast between a blue
sky and the clouds. In most situations where color-contrast and tone adjustment
is involved, these filters work similarly for black-and-white video as for film.
Using filters for contrast
control can be a matter of artistic preference, or of necessity. It is possible
for two disparate colors, say a certain orange and blue, to record as the identical
tone, eliminating any visible difference between them. Filters will lighten
objects of their own color and darken those of their complement. Complementary
color pairs are: green-red; orange-blue; violet-yellow. An orange filter in
the above case will darken the blue, and lighten the orange; a blue filter will
perform the reverse.
A green filter, such as
Wratten #11, can be used to lighten green foliage, to show more detail. It may
also be used to provide more pleasing skin tones outdoors, especially against
blue sky.
Any filter used for the
above purposes will have a greater effect if slightly underexposed. Its function
depends on absorbing light of its complementary colors to increase the proportion
of light of colors similar to itself. Exposure compensation is often needed
to allow proper image density, but the relative difference is reduced by the
addition of light at the absorbed wavelengths through additional exposure. Back
to begining
FILTERS
FOR COLOR
General
Information | Color
Conversion Filters | Color
Compensating Filters
Decamired® Filters | Discontinuous
Spectra Lighting Correction
Mixed Lighting Situations | Color-Grad®
Gradated Color Filters
Coral Filters | Sepia Filters | 812®Filter
| Didymium Filters
Differences Between Camera and Lab/Post Correction (Film
& Video)
LL-D® | Back to top
General
Information
Recording color involves knowing more about light sources than is necessary
for black-and-white imaging. Sunlight, daylight, exterior lighting at different
times of day, incandescent, fluorescent, as well as other artificial sources,
all have color characteristics that vary significantly. We see images through
our eyes only after they are processed by our brain, which has the ability to
make certain adjustments to the way we see color. White will still appear white
to the eye in various lighting, so long as we don't have more than one type
visible at a time. Film has no such internal compensation. It is designed to
see only a certain type of light as white - all others will appear different
to the extent of their difference. Filters are required to provide the necessary
fine-tuning.
Knowing that light is a
form of energy, we can theoretically view it as energy emitted from a hot object,
usually termed a 'black body,' that gives off light as a function of its temperature.
The color of that light can be measured in degrees Kelvin (1K). The normally
encountered types of light can be categorized by certain anticipated color temperatures,
or can be measured with a color temperature meter. Back to
begining
Color Conversion Filters
Color Conversion filters are used to correct for sizable differences in color
temperature between the film and the light source. These are comprised of both
the Wratten #80 (blue) and the Wratten #85 (amber) series of filters. Since
they see frequent outdoor use, in bright sunlight, the #85 series, especially
the #85 and #85B, are also available in combination with various neutral density
filters for exposure control.
Light Balancing Filters
Light Balancing filters are used to make minor corrections in color temperature.
These are comprised of both the Wratten #81 (yellowish) and the Wratten #82
(bluish) series of filters. They are often used in combination with various
neutral density filters for exposure control. They are often used in combination
with Color Conversion filters. Certain #81 series filters may also be available
in combination with various neutral density filters for exposure control. Back
to begining
Color Compensating Filters
Color Compensating filters are used to make adjustments to the red, blue or
green characteristics of light. These find applications in correcting for color
balance, light source variations, different reversal film batches, and other
color effects. They are available in density variations of Cyan, Magenta, Yellow,
as well as Red, Blue, and Green filters. Back to begining
Decamired® Filters
Decamired filters are designed to more easily handle unusual color temperature
variations than the previously mentioned filters. Available in increments of
both a red and a blue series, Decamired filters can be readily combined to create
almost any required correction. In measuring the color temperature of the light
source, and comparing it to that for which the film was designed, we can predict
the required filtration fairly well.
A filter that produces a
color temperature change of 100 degrees K at 3400 degrees K will produce a change
of 1000 degrees K at 10,000 degrees K. This is because the filter relates to
a visual scale of color. It will always produce the same visible difference.
A color change of 100 degrees K at the higher temperature would hardly be noticed.
To allow simple calculation
of such differences, we convert the color temperature into its reciprocal, that
is, to divide it into '1.' Then, since this is usually a number with six or
more decimal places, we multiple it by 106, or one million, for convenience.
This is then termed the 'mired value,' for micro reciprocal degrees. It identified
the specific change introduced by the filter in a way that is unrelated to the
actual temperature range involved.
To see this more clearly,
let's look at the following changes in color temperature from both the degree
and mired differences. Numbers are degrees Kelvin, those in parentheses are
mireds:
9100 (110) to 5900 (170)
= difference of 3200 (60)
4350 (230) to 3450 (290)
= difference of 900 (60)
4000 (250) to 3200 (310)
= difference of 800 (60)
From this, you can see that,
although the degree differential varies as the range changes, the actual filtration
difference for these examples, in mireds, is the same.
To use this concept, subtract
the mired value of the light source from that of the film. If the answer is
positive, you need a reddish filter; if negative, use a bluish filter. Mired-coordinated
filters are termed as decamireds. Mired value divided by ten yields decamireds.
The 60 mired shifts, above, would be produced by an R6 filter, where the higher
values were that of the lighting. Sets of such filters generally come in values
of 1.5, 3, 6, and 12 decamireds in both B (bluish) and R (reddish) colors. These
numbers are additive; that is, a pair of R3's produces an R6. An R6 plus a B6
cancel each other out to produce a neutral gray. Back to begining
Fluorescent and Other
Discontinuous Spectra Lighting Correction
Since filters never actually add color, but only absorb certain wavelengths
to increase the relative proportion of others, the original light source must
have the colors you want in it to start with. Some sources are totally deficient
in certain wavelengths, which cannot be added back using only filters. This
is particularly true of many types of metal halide lighting. With other lighting
types, such as fluorescent, color temperature measurements may not provide the
correct filter requirements since color temperature theory is based on having
a continuous spectrum, meaning light at all wavelengths. It is possible for
a light source to have a sufficient spectral distribution to emulate a correctable
color temperature when so measured, but its effect on film can be very different.
Fluorescent lighting generally
produces a greenish color overcast. Each of the many lamp types varies in color,
and it can be difficult to know the precise correction even with a color temperature
meter, a set of CC filters, and running some tests. There is available, however,
a filter type developed as an average correction for the most commonly encountered
fluorescent lamps.
As produced by Tiffen, this
filter is called the FL-D® for use with daylight corrected media, or the FL-B®
for use with tungsten corrected media. Both are designed to yield good-to-excellent
color under fluorescents, without the need for a meter and a variety of CC filters.
Back to begining
Mixed Lighting Situations
A question often arises of what to do when there is more than one type of lighting
used in a scene. The key to this is to first try to make all the light sources
behave the same. That is, to choose one that predominates, correct the camera
for that, and correct the other lighting with 'gel' filters made for them. You
can convert daylight coming through a window with a gel placed over the window,
that will make it a similar color temperature as the predominant tungsten, or
even fluorescent, lighting inside. Then correct the camera for that type of
light. There are many such combinations that will work, which one to choose
is often a matter of economics. Filtering a factory of fluorescents with gels,
or filter tubes, may cost far more than just gelling up the occasional window.
If there is no way to correct
all the lights for one color temperature, try to minimize the intrusion of those
for which you cannot correct to the camera. Sometimes, this can be used to advantage.
The cool blue light from outdoors through a window can make the tungsten-lit
interior seem that much warmer, and cozier. Once 'normal' color is within reach,
frequently a variation can be even better. It all depends on your purpose, and
the story you are telling. Back to begining
Color-Grad®
Gradated Color Filters
Similar to gradated ND filters (see earlier section for additional details),
Color-Grad color filters are also produced in a wide range of standard and custom
colors, densities, and proportions for many applications. A Blue-to-Clear filter
can add blue to a white, hazy sky without affecting the foreground. An Orange-to-Clear
filter can enliven a tepid sunset. Color can be added to the bottom of the scene,
as with a Green-to-Clear filter used to enrich the appearance of a lawn.
Stripe filters are another
type of gradated filter, having a thin stripe of color or neutral density running
through the center of the filter, gradating to clear on either side. These are
often used to horizontally paint various colors in layers into a sky, as well
as for narrow-area light balancing. Back to begining
Coral Filters
As the sun moves through the sky, the color temperature of its light changes.
It is often necessary to compensate for this in a variety of small steps as
the day progresses, to match the appearance of different adjacent sequences
to look as if they all took place at the same time. Coral filters are a range
of graded filters of a color similar to an 85 conversion filter. From light
to heavy, any effect from basic correction to warmer or cooler than "normal"
is possible. Corals can also compensate for the overly cool blue effect of outdoor
shade. Back to begining
Sepia
Filters
People often associate sepia-toned images with "early times." This makes Sepia
filters useful tools for producing believable flashbacks and for period effects
with color film. Other colors are still visible, which is different from original
sepia-toned photography, but appear infused with an overall sepia tint. Back
to begining
812®Filter
The Tiffen 812 is a mild warming filter. It finds use in adding additional color
to flesh tones. Bluish reflections from black skin can also be reduced. The
812 is such a useful addition that it is manufactured in combination with other
effects. These are called "warm" versions of Pro-Mist, Soft/FX, Polarizer and
others. Back to begining
Didymium
Filters
The Tiffen "Enhancing Filter" is a combination of rare earth elements in glass.
It completely removes a portion of the spectrum in the orange region. The effect
is to increase the color saturation intensity of certain brown, orange, and
reddish objects by eliminating the muddy tones and maximizing the crimson and
scarlet components. Its most frequent use is for obtaining strongly saturated
fall foliage. The effect is minimal on objects of other colors. Skin tones might
be overly warm. Even after subsequent color timing or correction to balance
out any unwanted bias in these other areas, the effect on reddish objects will
still be apparent.
Underwater Color Correction
Filters When imaging underwater, the light you are recording is filtered by
the water it passes through. Longer wavelength reds and oranges are absorbed
until only blue is left. The actual effect is determined by numerous factors,
such as light source (sun or artificial), water quality, and the water path.
The latter is the distance the light travels through the water. In natural (sun)light,
this is the depth of the subject from the surface plus the subject-to-camera
distance. For artificial lighting, it is the light-to-subject-to-camera distance.
The longer the water path, the greater the filtering effect of the water. In
many cases, certain color compensating filters can absorb enough shorter wavelengths
to restore better color balance. The difference between corrected and uncorrected
color can be dramatic. The use of faster speed films, cameras (video) and lenses
will facilitate the use of light absorbing correcting filters. Back
to begining
Differences
Between Camera and Lab/Post Correction (Film & Video)
It is the job of the lab timer to fine-tune the finished color rendition of
the production. This accounts for variables in exposure, print stock and processing.
Timing can also be used to impart certain color effects, both for densities
available in the film emulsion to work with, and is limited to the range of
variation of the optical printer. These are much more limiting than the multitude
of colorants in the real world, and the number of ways in which adjustments
can be made at the camera. Filtering on the camera brings the lab that much
closer to the desired result, providing a greater latitude of timing options.
The same is true for video post-production color correction.
With film, there will be
times when counting on the lab is either the only choice, or can produce some
unusual effects. When faced with a low light situation, in daylight using tungsten
film, it may be necessary for exposure reasons to pull the 85 filter and correct
in the printing. When you do this, however, neutral gray tones will appear slightly
yellow, even when all else looks correct. This effect can be used to artificially
enhance lush green foliage colors through the addition of yellow. It may have
other uses, but you will not achieve the same result as if you had used the
85 filter. Back to begining
LL-D®
The LL-D was designed to help in the above situation. It requires no exposure
compensation, and makes sufficient adjustments to the film to enable the timer
to match the color of a properly 85-filtered original. It is not an all-around
replacement for the 85. Use it only where needed for exposure purposes, and
for subsequently printer-timed work. Back to begining
SPECIAL
APPLICATION FILTERS
Day-For-Night
| Close-up and Split-Field Diopter | Back
to top
Contrast Viewing Filters
Balancing lighting by eye is a matter of experience. Decisions can be aided
through the use of contrast viewing filters. These are designed to handicap
the eye, with its much greater range of apparent densities, to resemble the
range of the various types of film. Use contrast viewers to judge relative highlight
and shadow densities. There are viewers for black-and-white film, as well as
various viewer densities for color film. A darker viewer is used for slower
film speeds, where you would tend to use brighter lighting. Faster film, which
can be used in dimmer settings would require a lighter viewer.
The Tiffen #1 viewer is
for black-and-white imaging. The #2 viewer is for film speeds to 100; #3 is
for faster film. They can be used for video, as well, with the #3 being better
suited for lower light levels. The green #4 viewer is for process photography.
The blue #5 is for blue screen work, as well as for setting up color video monitors.
Back to top
Day-For-Night
Day-for-night photography is an effect that makes a scene recorded in daylight
to appear as if it were at twilight. This is usually accomplished by the use
of a filter that both underexposes by about two stops, and can also produce
a bluish color overcast. Lighting, contrast, and other factors contribute to
the reality of this effect. Back to beginning
Close-up and Split-Field
Diopter Lenses
Close-up lenses allow for closer focusing than would otherwise be available
with the unaided camera lens. These are especially ideal for nature subjects.
Cutting such a lens in half produces the Tiffen Split-Field lens. This can be
used to have two fields of focus, one very near, and the other very far, in
one scene. Back to beginning
OTHER
FILTER CONSIDERATIONS
Effect
of Depth of Field and Focal Length Changes
Multiple Filter Use | Secondary
Reflections
Custom (Homemade and Field-Ready) Filters
Back to top
Effect of Depth of Field
and Focal Length Changes
Standard color filters generally function without change through variations
in depth of field and focal length. This may not be true of many of the "special
effect" filter types. There are no solid rules for predicting the variation
in filter effect due to depth-of-field or focal length changes. There are some
things we can expect, however. Let's look at a fog/mist type filter that causes
a light to glow, or flare. Take the example of a certain grade filter where
we can see that the ratio of light diameter to glow diameter is, say, 1:3. As
we view this through a changing focal length, we will see that the ratio remains
the same, although the magnification will vary accordingly. So the decision
to use a filter of a different grade to maintain a certain appearance at different
focal lengths will be based on wanting to change the ratio, as opposed to any
otherwise corresponding relationship. Tests are advisable for critical applications.
Sizes, Shapes, and Mounting
Techniques Filters are available in round and rectangular shapes in many sizes.
Round filters generally come supplied with metal rings that mount directly to
the lens. Frugal filter users might find it preferable to use adapters allowing
the use of a set of filters of a single size with any lenses of equal or smaller
sizes. Round filters also can be supplied with self-rotating mounts, where needed,
as for polarizers. They can be readily stacked in combination. Rectangular filters
require the use of a special filter holder, or matte box. They offer the additional
benefit of allowing slidability, for effects that must be precisely aligned
within an image, such as gradated filters. In all cases, it is advisable to
use a mounting system that allows for sturdy support and ready manipulation.
In addition, the use of a lens shade at the outermost mounting position (from
the lens) will minimize the effect of stray off-axis reflections. Back
to beginning
Multiple Filter Use
When any single filter is not enough to produce the desired results, use combinations.
Choose carefully, to minimize the number required. Usually the job can be done
with no more than three filters. Use filters that individually add to the final
effect, without canceling each other out. For example, don't use a polarizer,
which can increase color saturation, in combination with a low contrast filter
which reduces saturation, unless it works for some other reason (the polarizer
could also be reducing reflections, for instance). Generally, the order they
are mounted in is not important. Back to beginning
Secondary Reflections
Lighting can cause flare problems, especially when using more than one filter.
Lights in the image pose the greatest difficulties. They can reflect between
filter surfaces and cause unwanted secondary reflections. Maintaining parallelism
between filters, and further aligning the lights in the image with their secondary
reflections where possible, can minimize this problem. In critical situations,
it may be best to make use of a matte box with a tilting filter stage. Tilting
filter(s) of good optical quality only a few degrees in such a unit can divert
the secondary reflections out of the lens axis, out of the image, without introducing
unwanted distortion or noticeable changes in the filter's effect. Back
to beginning
Custom (Homemade and
Field-Ready) Filters
There will be times when you need an effect and don't have time to obtain one
ready-made. Certain effects can be produced that, although different from factory
filters, can be useful in a pinch, or for unusual custom situations. Net diffusion
effects can be produced as they were originally, by stretching and affixing
one or more layers of stocking material to the lens end, held in place with
a rubber band. There are also numerous things you can do if you have a clear
filter (or several) available. Petroleum jelly can cause flare or diffusion,
or even some star-like streaks, depending on its application, to a clear filter,
spread with a finger or cloth. The chief benefit here is that the effect can
also be applied only to selected portions of the scene. Breathing on a clear
filter can produce interesting, but temporary fog-like results. Using cut gels
can simulate certain gradated filter effects. When doing this, be sure to keep
the filter close to the lens, and use larger lens openings, to keep the visible
edge as soft as possible. Back to beginning
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