If you ask most consumer-camera owners why they keep a filter on their lens, a majority will most likely reply, “For protection.” Although filters do, in fact, protect the surface of your lens against dust, moisture and the occasional thumb print, the primary function of lens filters is really to improve the image quality of the pictures you take—depending on the filter you’re using and how you use it—in a variety of obvious and not-so-obvious ways.
The most basic filters are ultra-violet reducing filters (UV), Skylight filters and protection filters, which depending on the manufacturer are either glass filters with basic anti-reflective coatings, or in some cases, merely plainclothes UV filters, which isn’t dishonest. To keep the front element of your lens clean and safe, any of the above will suffice, but if you’re looking to protect your lens and improve the image quality of your stills and video, you’re going to want to purchase a UV or Skylight filter.
UV filters, also referred to as Haze filters, are designed to cut through the effects of atmospheric haze, moisture and other forms of airborne pollutants, each of which contributes to image degradation. UV/Haze filters are available in varying strengths. If you plan on photographing near large bodies of open water, at higher altitudes, in snow or other conditions that magnify the intensity of ambient ultra-violet light, you should definitely consider a stronger level of UV filtration (UV-410, UV-415, UV-420, UV-Haze 2A, UV-Haze 2B, UV-Haze 2C and UV-Haze 2E). Depending on the strength of the UV coatings, UV filters appear clear, or in the case of heavier UV coatings, have a warm, amber-like appearance and require anywhere from zero to about a half stop of exposure compensation.
An alternative to UV/Haze filters are Skylight filters, which are available in a choice of two strengths—Skylight 1A and Skylight 1B. Unlike UV/Haze filters, which have a warm amber appearance, Skylight filters have a magenta tint that is preferable when photographing skin tones or using color slide film, which depending on the film stock often has a blue bias that is typically counterbalanced by the magenta tint of Skylight filters.
Regardless of their strength, skylight filters do not have any effect on the camera exposure, are equal to UV filters in terms of cutting through atmospheric haze and protect your lens against dust, moisture and fingerprints that can all be damaging to lens coatings if not removed in a timely manner.
Even though one UV filter might appear indistinguishable from another UV filter costing two or three times as much, the differences between them can be considerable, beginning with the quality of the glass used in the manufacturing process. Though one would suspect there’s little difference between one piece of glass and another, make no mistake about it—there’s glass and there’s glass, and the differences can make a difference in the quality of your images.
The primary criteria of good glass versus so-so glass are the chemical composition of the glass, how it was made and even where it was made. These are followed by the thickness of the glass (the thinner, the better) and the coatings used to minimize flare and maintain optimal color and contrast levels. Although the differences between an inexpensive filter and a pricier filter may not be all that apparent when photographing with a kit zoom lens, they become increasingly obvious when used with costlier, higher-performance lenses.
In the case of color and Polarizing filters, which typically consist of a thin layer of color film (or Polarizing material) sandwiched between two layers of glass, the film is usually bonded to the glass layers in pricier filters. This eliminates air surfaces and other irregularities that can negatively affect the optical purity of the filter when compared to less expensive filters designed to perform the same functions.
The other difference between entry-level filters and the pricier versions has to do with the retaining rings, which in the case of cheaper filters are invariably made of aluminum (a relatively soft metal) that are subject to denting and jamming if they're not screwed on straight. Conversely, the retaining rings used on pricier filters are most always made of brass and as such are less likely to get jammed onto your lens and dent when they strike hard surfaces.
The bottom line is if you go the extra mile (and expense) by purchasing a better lens, you shouldn’t compromise the results of your investments by saving a few dollars on the filter.
Kaeseman filters, which are invariably Polarizing filters, are manufactured with more weatherproofing seals than non-Kaeseman filters. They are worthy investments if your photographic interests include traveling to and working in damp, extreme climates.
If you photograph landscapes—or any outdoor scenics for that matter—you should certainly have a Polarizing filter handy at all times. Polarizing filters are best known for making clouds seemingly pop out from darkened blue skies, saturating colors and eliminating glare and reflections from the surfaces of water, glass and other polished surfaces.
Polarizing filters are mounted in a secondary ring that you manually rotate while viewing your subject through the viewfinder until you dial in the desired level of Polarization. The downside of Polarizing filters is that you lose about three stops of light in the process of optimizing the image, but the results cannot be mimicked using Photoshop plug-ins or other forms of post-capture voodoo.
Polarizing filters are also available combined with additional filtration such as warming filtration (81A, 81C, 81EF, 85, 85B), Enhancing and Intensifying, Skylight, UV/Haze and a measure of diffusion.
Polarizing filters are available in two formats: linear and circular. Though they look and perform identically, circular Polarizing filters are designed specifically for use with autofocus lenses while linear are best used with manual-focus lenses. Circular Polarizers, on the other hand, can be used with AF or MF optics with equal results.
Neutral density (ND) filters are essentially gray-toned filters designed to absorb calibrated degrees of light as it passes through the lens. Most commonly broken down in 1/3, 2/3 and full-stop increments, ND filters are more recently also available as variable-density filters that you can infinitely adjust by rotating the filter on its mount as you would a Polarizing filter.
There are many applications for ND filters. Chief among them is their ability to allow you to shoot at wider f-stops under bright lighting conditions. ND filters are used extensively by filmmakers and videographers as tools that allow them better exposure control due to the limited shutter-speed options afforded by the cinema and video process.
ND filters also make it possible to blur the movement of pedestrian traffic and flowing water under bright lighting conditions by allowing you to drop your shutter speeds while maintaining full control of how much or how little depth of field you desire, based on the amount of ND filtration you place in front of the lens.
Neutral density filters are even, edge to edge, in their degree of density while graduated neutral density filters are typically clear on one end and slowly build up density toward the opposite side of the filter. Graduated ND filters are most commonly used to even out scenes containing extreme exposure variations on opposite sides of the frame.
Examples of these types of scenarios include landscapes in which the top of a mountain is bathed in sunlight, while the valley below lies in shade; and multi-story atriums where the primary source of illumination is an overhead skylight from which the light gradually falls off as it approaches the lower levels. Graduated filters can also be used in evenly lit areas to darken the sky or foreground for stylistic reasons.
In addition to neutral graduated filters, colored grad filters are also available, and are useful for adding a touch of subliminal color into a scene while darkening the foreground or background.
While warming (adding yellow to the scene) and cooling (adding blue to the scene) can be applied to an image file post capture in Photoshop or other image-editing software, there are still those—including film shooters, who prefer to filter the lens at the time the exposure is made.
Most photographers warm or cool their images for aesthetic or mood reasons. A bit of warming is often desired for portraits, or when photographing at midday during the summer months when the sun's light can be bluer and harsh. Warming can also be effective when taking pictures on overcast or rainy days.
Conversely, cooling filters can be used to correct color in images in which the color temperature is too warm to suit your intentions. Warming filters include all 81 and 85-series filters, and cooling filters include all 80 and 82-series filters.
When using cooling, warming and other color filters with digital cameras, it’s important to set the White Balance to a setting close to the ambient color temperature, i.e. Daylight, Overcast, Tungsten, Fluorescent, etc., and avoid Auto WB, which will intuitively try to correct, according to its own parameters, the mood and tone you’re trying to establish. Auto WB may not render results that are in agreement with your personal vision.
Enhancing and Intensifying filters are modified to cut some of the orange portion of the color spectrum, which results in higher saturation levels in reds and cleaner, less muddy interpretation of earth tones. They are especially popular for photographing fall foliage and landscapes.
While color filters do make everything look red, yellow, green or whatever color you might place in front of the lens, their most common use is for black-and-white photography.
When shooting black and white, the color of the filter being used blocks that color from reaching the film (or sensor) surface, which depending on the filter color and subject matter, can drastically change its tonal qualities. As an example, shooting through a yellow filter better delineates clouds against blue skies. Orange filters further darken blue skies and make the clouds pop more, and red filters darken blue skies even more and make the clouds pop out most dramatically.
Green filters on the other hand, are effective at improving skin tones in black-and-white portraits.
Color-correction filters, also called cc filters, consist of cyan, magenta, yellow, red, green and blue filters. Each of these is available in 10% increments and is used for modifying or correcting the color balance of mismatched or irregular light sources. The need for cc filters is not as great in these digital days as it was in the time of film. Nevertheless, they are still used by many photographers who would rather correct their images at the time of capture.
As with warming, cooling and other color filters, it’s advisable to avoid the Auto WB setting on your digital camera when using cc filters and instead choose daylight, overcast, tungsten, fluorescent or whatever setting is closest to the ambient lighting conditions under which you’re working.
Aside from the glass screw-on filters most photo enthusiasts and pros depend on, there are also polyester, gelatin and resin filters, which are used for both creative as well as technical applications. Usually square or rectangular in form, these filters are most commonly used with filter holders or matte boxes that fit in front of the lens via screw-in or friction mount filter holder adapters. The filters are dropped into place in slots that keep the filters flat and parallel to the front lens surface in order to maintain optimal image quality.
It depends on what you mean by "better." If you mean sharper, some of these filters, especially the thinner resin and gelatin filters—depending on the brand and material—are optically purer than glass. They are also lighter to transport, and if you plan on purchasing an entire series of filters, these alternatives will be less expensive than a comparable set of glass filters.
These alternative filters are also handy if you have lenses with differing filter threads. All you need is a single set of step-down rings, starting with the largest thread down to the smallest size, to go along with the filter holder. (These same step-down rings can also be used with screw-in glass filters if you are using lenses with differing filter thread sizes—there’s no need to purchase multiple sets of filters.)
The downside however is that non-glass filters are easily damaged and in the case of gel filters, near impossible to clean when smudged by an errant fingerprint. So if you do go this route, be extra careful when handling them and by all means invest in a box of disposable plastic or cotton gloves.
Slim filters have narrow profiles and sometimes lack threads on the forward side of the filter ring. Slim filters, which are available in almost every filter size, are designed for use with lenses featuring angles of view wider than about 74°, or the equivalent of a 28mm lens. By utilizing a thinner retaining ring, the filter is less likely to vignette the corners of the frame. Depending on the make and model, many kit zooms require thin or slim-mount filters.
There are many types of creative and technical filters available for pros and serious enthusiasts alike. Included among them are filters that produce prism and star-like patterns, filters for close-ups, diffusion, infrared imaging, as well as contrast control. Their creative applications are up to you!