Filter Primer
How to use filters creatively to improve your digital photography.

By Bob Shell

Lens hoods

Many beginning photographers buy their camera and lens and never consider buying a lens hood, also called lens shade. Sometimes these come with lenses, but often they don‚t. If you didn‚t get a lens hood with your lens it is the very first accessory you should add.

There are several types of lens hoods, but the most commonly encountered ones are hard, made from rigid plastic or metal, and soft, made from rubber. So long as the lens hood is the right length for the focal length of the lens you are using, all of these work just fine. Some photographers prefer the rubber ones because they provide extra shock protection to the front of the lens. If the lens hood is the wrong length for the lens it will not provide very much flare protection (if too short) or will cut off the corners of the image (if too long), so buying the right one is important. In many cases your lens instructions will specify the proper hood. If not, your best bet is a knowledgeable sales person at a good camera store.

The purpose of a lens hood is to block light from the lens that is not contributing to the image. Excess light from outside the image area can cause problems if not blocked. This will be seen as an overall gray cast over the whole image and a loss of contrast in the image. You may also get ghost images and reflections caused by stray light bouncing around inside the lens. In the worst cases you will lose all detail in the image. The technical term for this is veiling glare, and a proper lens hood will greatly reduce or eliminate it.

Filter Basics:
There are two schools of thoughts about filters for digital photography. Some feel that there is nothing you can do with a filter on the camera that you can‚t duplicate after the fact in Photoshop. The other school of thought, to which I proudly belong, believes that there are many effects produced by photographic filters which can not be duplicated in software after the fact. Of course there are many effects which can be done with Photoshop or plug-ins which can‚t be duplicated with lens filters.

There is a lot of confusion about just what filters are and just what they do among beginning photographers. Many think that they somehow add something to the image that wasn‚t there in the subject. Just as with filters used to clean water, remove unwanted things from gasoline, etc., photographic filters follow the dictionary definition of a filter and only remove things. What they do for us in photography is remove unwanted types or quantities of light. If the light falling on your subject contains too much of a particular color of light, say it is too blue as an example, then you want to use a filter on your camera which will subtract the excess blue to give a natural look to your photographs. Color altering filters are most effective when you are using film, but in digital photography you can generally deal with color casts by setting the proper white balance.

Many times you will be told by camera store clerks or read in books that you should always keep a filter on the front of your lens to protect it. Except in severe conditions like blowing sand, salt spray from ocean breakers, industrial environments, and a few others, this is bad advice. Camera stores often push filter sales because filters are very high profit items and when they add filters and other accessories to a sale they may well make more on the filter and accessories than they do on the camera. Even the best filter degrades image quality slightly, cheap filters a lot more. Because I want the sharpest possible image I want nothing between my lens and my subject but air. Generally speaking, if you are concerned about protecting the front of your lens against impact damage, a good lens hood will do a better job of protecting the lens than any filter. A filter also adds two new surfaces which must be kept clean, and two additional surfaces which may reflect light and cause image degrading flare. Professional photographers know all this, which is why you will not see filters on the front of their lenses unless put there for a specific purpose to modify the image. If you must put a filter on the front of your lens, insist on only the very best. Nothing can kill the quality of a great lens faster than a poor quality filter on its front.

The brief filter guide that follows is intended to give you information on the most commonly encountered types of photographic filters. It is not intended to be inclusive as there are many other types of filters for special photographic purposes. For additional information on filters you can check the web site at the end of this article.

UV and Sky 1A Filters
UV (also called Haze) and Sky 1A (or Skylight) filters serve two purposes. Both filter out excess UV which can cause a bluish cast when working at high altitudes. Since the cement used in almost all modern photographic lenses is designed to absorb UV, a UV filter is unnecessary except when working at high altitudes. If you are working in situations in which damage to the front element of your lens is likely, a UV filter can provide protection. I use them when working in the desert on windy days, when working close to the ocean when waves are high and generating a lot of salt spray, when photographing inside some types of factories, etc.

A Sky 1A (Skylight) filter is a UV filter which is also tinted pale pink or salmon color. This removes some of the blue from a scene and gives a warmer color balance to the images. Some people find they prefer the rendition of flesh tones they get when using a Sky filter. Some filter makers also produce Sky or Skylight 1B filters, which have a stronger pink or salmon tint.

Haze-1 Filter
Sometimes very hazy skies will cause loss of distant detail due to UV reflected from the haze. In such cases the stronger Haze-1 filter may help bring out detail as in these examples.

There are also other special UV filters for situations in which the light has a very high UV content. These would mostly be used at very high altitudes.

Polarizing Filters
The polarizing filter is one example of an optical filter which produces an effect which can not be duplicated after the fact.

Light falling on subjects gets reflected off and bounces around in all directions. We see some of this light as reflections and glare. The light falling on subjects is unpolarized which means that the wave property of light has modulations in all directions around the line of its travel. The light reflected from most subjects (except polished or plated metal) becomes partially or wholly polarized when reflected, meaning that the wave modulations are mostly or completely on one axis. A polarizing filter allows light to pass through which is modulated only on one axis and absorbs light modulated on all other axes. This absorption is why a polarizer looks darker than a clear filter.

By rotating the polarizing filter you can select which light passes through it to form your image. If there is an annoying reflection from glass, water, etc., in the scene, you can filter out all or most of that reflection because the light forming it was polarized when it was reflected off the surface. You can eliminate all of the reflection or only part of it by careful selection of the rotation angle of the filter. Because a lot of the haze in a blue sky is made up of reflected light, which also has become polarized in being reflected, you can make a blue sky bluer by selecting the angle of the polarizing filter. You can see the effect as you turn the filter if you have an SLR camera.

There are two types of polarizing filters available and many people are totally confused about them. A basic polarizer as described above is referred to as a linear polarizer. Linear polarizers are also what are used in polarized sunglasses. They act simply, filtering out light modulated on all but one axis. And the light which passes through them is polarized on that axis. Such a simple polarizer was fine for simple cameras, but today‚s cameras are not simple. They employ their own polarizers internally in their light metering and autofocus systems, and putting a simple linear polarizing filter on the front of one of these cameras can cause errors in exposure and focus, or disable both automatic metering and focus. For such modern cameras a second type of polarizing filter was developed, called a circular polarizer. A circular polarizer is really two filters on top of one another in a single ring. The first one is a simple linear polarizer as described above. The second one (called a quarter wave plate or Kasemann plate) takes the light passed through the first one and converts its linear polarization into circular polarization, or more simply it depolarizes it. This does not lose any of the effect from the polarizer because the light has been fully polarized prior to passing through this depolarizing plate.

You don‚t need to know the technical stuff, though, to use a polarizer. If your camera has through the lens metering and/or autofocus, as almost all do today, you will need a circular polarizer.

Polarizing filters are also available in neutral, which do not change the color balance of the scene, and warm polarizers which produce a warmer color balance.

These photos show the effect of a circular polarizer on reflections. Note that you can hardly see the woman in the first photo. She is clearly visible in the second photo after the photographer rotated the polarizer until the reflections were eliminated. The third photo shows the effect of a warm polarizer.

Color Correction Filters
The effects of color correction filters can, in most cases, be duplicated in the computer, and they are not used to much in digital photography. There may be occasions when you prefer to produce these effects at the time of shooting, though, so it helps to be aware of what these filters do. You can also accomplish similar effects with custom white balance on your camera and set the white balance with special colored cards (www.warmcards.com).

Sometimes we want to change the mood of an image by making it warmer or cooler than it appears in reality, or to correct for color casts in the light falling on the subject. This is where the filters in the 80, 81, 82, and 85 series are useful. As with the Sky filters mentioned earlier, these filters come in more than one strength, denoted by A, B, C, etc., B is stronger than A, C stronger than B, and so on.

80A and 80B
The lighting used in most homes is provided by ordinary light bulbs which use a tungsten filament. For this reason we refer to this as tungsten light. The 80 series of filters is for use in balancing photos to provide natural-looking color when exposed under this type of light. The 80A filter is for use with home lighting while the 80B is for use with photographic flood lamps.

85, 85B and 85C
These filters do just the reverse of the 80 series, and are intended to allow you to use tungsten light balanced film outdoors in daylight.

81A, 81B, 81C and 81EF
This series of filters is used to correct for the cool effect we often see in natural light outdoors in shadows or on heavily overcast days. Also useful with some types of electronic flash which have too cool a color balance.

82A and 82B
These filters, sometimes called Morning and Evening filters compensate for the overly warm color balance encountered early in the morning or late in the afternoon.

FL-B, and FL-D
These filters are designed to correct color when photographing under fluorescent lights which often produce an unpleasant green cast in photos. FL-D is for use with daylight balanced film and FL-B is for use with tungsten balanced film.

Neutral Density Filters
Neutral density filters are simply filters which absorb all colors of light. They are used to reduce brightness in very brightly illuminated subjects. They are also very useful when you want to use a wider lens aperture to reduce depth of field when working outdoors in bright light. They come in a variety of densities for more control.

812 Filter
The 812 filter is only available from Tiffen. It is a special warming filter designed specifically to improve skin tones. It is particularly useful in the shade and on heavily overcast days.

Enhancing Filter
This special filter makes reds, oranges, rust browns, and similar colors brighter while having a minimal effect on other colors. It is particularly useful when making photos of autumn foliage.

Fog Filters
Fog filters are available in different strengths and are used to create the illusion of fog and haze when none is present. They can produce very romantic effects when used with care, but tend to produce clichés when used without care or too often. The photos below were taken using the Tiffen Double Fog filter, which produces a stronger effect.

Sepia Filters
Sepia filters can produce a romantic, old-fashioned look in color photos, adding a warm brown look to the image.

Star Effect Filters
We‚ve all seen these used, and overused, on television. They produce pointed stars of light wherever there is a specular highlight on the subject. They can be good for lights at night, sparkly jewelry, and other subjects with sparkle.

Close-Up Filters
These are often called filters, so I am including them here. Actually they are not filters at all but high quality magnifying glasses in threaded rings so they can be screwed onto the front of your camera lens to allow it to focus closer. They produce excellent results for general photography and are a much less costly alternative to expensive macro lenses, particularly for the photographer who does not specialize in close-up work but wants to extend the close-up capability of the camera occasionally.

Hollywood Special Effects Filters
While most makers of filters offer some special effects filters in their line, they have not really specialized in them. Tiffen, on the other hand, has devoted much time and research into developing their line of professional special effects filters which were originally used by the motion picture industry and television production. Many of these special filters are also available for the still photographer and amateur cinematographer/videographer. The filters described below are from the Tiffen Hollywood/FX series.

Pro-Mist Filters
These are specially designed filters which produce a softening effect without destroying subject detail. You‚ve seen many of your favorite actresses through them over the years. They de-emphasize facial lines and wrinkles. They are also good for providing a glamorous mood in outdoor scenes. Below is an example of the Pro-Mist 2 filter.

Black Pro-Mist
This filter somewhat emulates the effect of shooting through a black mesh scrim, often done in films, or stretching a piece of black stocking over the front of a lens. It is more subtle than the Pro-Mist and Warm Pro-Mist filters. It tones down highlights and lowers contrast but does not lighten shadows as much as the regular Pro-Mist filters. Sometimes the effect it produces is described as a pastel effect.

There are also „warmš Pro-Mist filters and a „warm blackš that combines a Black Pro-Mist filter with an 812 warming filter.

A special type of softening filter which smoothes over fine detail without affecting larger detail in the subject. It creates a softer look without looking mushy. As with others the Soft/FX is also offered in Warm Soft/FX.

Contrast Control Filters
Often you are faced with situations which are just too contrasty for the film to capture and you know you will end up with washed out highlights with no detail, blocked up shadows with no detail, or in the worst cases, with both. Contrast Control Filters lower the overall contrast of a scene without softening it, bringing the contrast range of the subject within that of the film. The one I use when faced with this situation is the Tiffen Ultra Contrast which is so unique that it was given a Technical Achievement Award by the Academy of Motion Picture Arts and Sciences. This filter is very popular with motion picture and television producers.

Hollywood Star
These are special variations on the common star filters mentioned above. There are four versions, North Star, Hyper Star, Vector Star and Hollywood Star, named for the types of stars they produce around highlights in the image.

For more info on filters: http://www. tiffen.com



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