Filters 101
There are thousands of different filters available, in confusing arrays of brands, colors, purposes, sizes, types, etc. Filters are extremely important for some genres of photography, and less-so for others. For instance, sports and studio photographers generally have little need for filters, while landscape and scenic photographers have a great need. This article will only provide a simple guideline on the basic filters usable for either digital or film cameras.
UV/Haze/Skylight Filters: This class of filter helps correct bluish atmospheric haze often visible in the distance of landscape photographs. The UV/Haze filter does so by blocking ultraviolet rays; the skylight filter by adding a slightly warm color to the photograph.
These are the first filters new photographers will be exposed to. When you buy a camera or lens, the salesperson invariably tells you this type of filter is a "necessity" for "lens protection." They most likely will not tell you about the actual purpose of these filters, only that "it is far better to scratch a $17 filter than to scratch the front element of an expensive lens."
There are two trains of thought concerning filters as lens protectors. One as mentioned above: to protect from "boo-boos." The other train of thought (and the one this writer adheres to): a lens cap provides far greater protection (ALWAYS use lens caps when transporting equipment!). Adding unneeded surfaces of glass to a lens increases the likelihood of introducing lens flare and degradation of image quality to photographs. These filters should be used as protectors in harsh environments; windy days where dirt or sand can sandblast a lens, seaside to protect from salt water, and from fingerprints, all which can erode the coating or stain a lens front element.
If you decide to use one of these filters for lens protection, a suggestion for choosing: Effects of UV/Haze filters are ONLY evident when using telephoto lens… effects are not visible with wide-angle lenses. Skylight filters add an almost imperceptible warm color cast to all photographs. Use UV/Haze filters on telephotos to obtain some effect on distant vistas; use Skylight filters on wide angle lenses. You will find a skylight filter also provides a benefit by lessening the cooling (bluish) effect of electronic flashes.
Polarizing Filters: This class of filter is the most useful filter to possess, and one of the most expensive. Their purpose is to remove polarized light from a scene, and they provide several benefits:
a) Darken the blue color of the sky.
b) Help prevent blown-out (all white, featureless) skies.
c) Increase contrast between blue sky white clouds, rendering dramatic effects.
d) Remove glare from foliage, ground, and rocks.
c) Remove reflections from water and glass (but not from metallic objects!).
d) Add saturation to colors and increases vibrancy to photographs.
Polarizers are available in two main types: Linear and Circular. The linear version only works for rangefinder, view, and manual focus cameras. They will affect focusing and metering capabilities on autofocus cameras! A circular polarizer will work for all cameras. So, if you use more than one camera type, use circulars only to eliminate the possibility of installing the wrong type of polarizer.
A consideration when purchasing a polarizing filter: With this filter more than any other basic filter, you will find a MAJOR difference in performance from brand to brand. This is one filter it is best not to settle for the cheapest… on polarizers you do get what you pay for! A low-end polarizer degrades image qualities, loosing clarity and details, especially in shadows. A low end polarizer reduces contrast and sharpness, changes colors of the image, can turn shadows blue, and provides only minimal polarization effects. High grade polarizers will not degrade images with loss of clarity, details or sharpness, or make shadows go blue, and they will have a much wider range of effect. Consider the Hoya HMC as the cheapest filter to consider when purchasing this very important tool. Suggestions for a quality polarizer: Singh-Ray, Heliopan multi coated or B&W Kaesemann multi coated.
In addition to Circular and Linear polarizers, there are "warming polarizers." These have built in warming effects in addition to the polarizing effect. It is very common to use warming and polarizing filters together, and warming polarizers do the job of two filters while reducing the possibility of vignetting when using wide angle lenses.
The polarizer is the most frequently misused filter. Many photographers always adjust the filter for maximum effect, being enamored with the rich blue skies the filter produces. However, while the dramatic sky is being produced, other reflections in the scene are being removed. Often those removed reflections are essential elements which made the scene special. Polarizing filters DO NOT have to be fully employed for maximum effect… and sometimes a little is better than a lot… pay close attention to all details affected by this versatile tool.
One more thing to consider when using polarizers: their effect is based on the sun’s position, with the strongest effects at a 90-degree angle from the sun. Pay attention to this effect especially with wide angle lenses, as one area of the sky can be considerably darker than the rest. This filter should not be used when shooting multiple images for stitching to create panoramas because of this variable effect. To obtain darker skies for this use, the use of gradient neutral density filters works far better.
Neutral Density filters: The purpose of this class of filter is to darken a complete scene, allowing the use of longer shutter speeds or larger apertures. They are used to great effect in panning (motion blur), or using high-speed film in bright conditions, and to create "slowed" water in surf or waterfall scenes. They are usually available in three strengths (some brands offer a wider range). General strengths available: .3 or 1-stop reduction / .6 or 2-stop reduction / and .9 or 3-stop reduction. When more reduction is needed, it is common to use more than one of these filters.
Gradient Neutral Density filters: The purpose of this class of filter is to darken a portion of the image, and used to maintain foreground details while keeping the sky from becoming bland and featureless. They are generally dark on one-half of the filter, gradually becoming clear on the other half. Two types are available: soft (for wide to standard length lenses), and hard (for telephoto lenses). They come in three strengths (.3 or 1-stop gradient / .6 or 2-stop gradient / .9 or 3-stop gradient). Generally the way to use them: 1) take meter reading of the foreground or area you want to preserve details in; 2) take meter reading of the sky; 3) determine the difference and 4) use the strength of gradient that darkens the sky approximately 1-1/2 to 2 stops above the details to be preserved. These filters are also often used stacked to obtain more effect as needed.
To properly use this filter system, a filter holder accepting square or rectangular filters should be used. This holder allows the filter to be slid up or down enabling the photographer to set the transition area of the filter (ie: near the horizon). Tiffen does produce these filters in a round variety, but the transition area occurs dead-center in the frame… where one usually does not want the conversion to start. The Cokin filter system produces an inexpensive filter holder that works not only with their filters, but most filter manufacturers also makes filters to fit this very popular holder.
A word of caution when using these filters: Everything in the darkened area will be affected. Be cognizant of trees, buildings, mountain tops, etc. projecting above the transition. Images can be ruined by placing this transition area in the wrong place. It is always best to "stop down" the lens to observe the effects of this filter.
Warming filters: The purpose of this class of filter is to remove bluish tinges that results from atmospheric haze, or mid-day photographs, or flash photography. They are also used for changing the "mood" of available light, making cold light warm, or warm light warmer. They are available in various strengths, ranging from very minimal to very strong. Strengths available: 81A (minimal), 81B. 81C, 81D, 81EF (very strong). The most commonly used warming filter being the 81B (which, if not wanting to buy a complete set would be the one to start with). The 81A is also effective for use with electronic flash units to provide a more pleasant light color.
Step-down or Step-up rings: These are conversion rings to be used for fitting different size filters on various lenses. If you look at the thread size of your lenses, you may find there are many different sizes of filters required. Buying a set of filters for each lens size can be cost prohibitive. Before purchasing filters, it would be wise to determine the largest filter size you require, and purchase all filters to fit this size. Then buy conversion rings so your large filters will fit on a smaller threaded lens.
The effects of most of the filters listed in this article cannot be duplicated accurately in editing programs. These valuable tools can dramatically improve your images, and are a worthwhile addition to your collection of photography equipment.
Glenn S. Mellen
[aka: Anchored_in_TX]
