UV Filters

Despite the fact that digital imaging sensors are nowhere near as sensitive to UV radiation as film, the protective properties of a UV filter on your lens are still quite justified. Regardless of how the image is being recorded, the probability of dust, moisture, smudges and scratches finding their image-compromising way onto your front lens element is equally inevitable and troublesome.

 There�s also a strong argument to support the idea that over time, the slow accumulation of micro scratches and the wear-and-tear of cleaning the lens surface probably adds up to more image-degrading effects than a good-quality filter in front of your lens could ever cause. From an economic perspective, even the most vocal critic of filters would gladly pay the price of replacing a shattered filter as opposed to the cost of replacing the front element of a lens.

The visual spectrum�the light we see with our eyes�consists of the colors red, orange, yellow, green, blue, indigo and violet. Mix them together and you get �white� light. The electromagnetic wavelengths of light are measured in terms of nanometers (nm), with the visual spectrum residing in the 390 to 750nm portion of the electromagnetic bandwidth. Just below the red end of the visual spectrum is infrared (approx 750nm to 1mm) and ultraviolet light resides just above the blue end of the visual spectrum (approx 10nm to 390nm). While we cannot see UV light, it nonetheless impacts the visual quality of the pictures we take.

UV affects image quality in several ways. When photographing outdoors UV light manifests itself in the form of haze, which can vary based on how close you are to large bodies of water or snow (water and snow both reflect sunlight, which in turn magnifies UV levels), altitude (the higher you go, the more UV light you encounter), and larger cities (reflective glass and metal-clad structures can also amplify ambient UV levels). This haze robs image detail, especially at longer distances with longer focal length lenses where cumulative haze densities can severely soften the sharp details of distant objects. In many respects, this neutralizes the argument against using filters for fear of compromising the resolving power of the lens, most notably telephoto lenses.

Unlike moisture-related haze, which can be controlled through the use of UV filtration, smog, a major component of urban haze, is not reduced by the use of a UV filter. The reason for this is that smog is made up of solid particles, not reflected light.

Not exactly. If you were to search for a 58mm UV filter on the B&H website you�d be shown a list of more than 30 filters ranging in price from under $10 to more than $270. Although both of these filters look alike and work the same way, they are likely as similar as two four-door sedans, albeit one made by AvtoVAS and the other by Mercedes. The criteria for determining the differences between each of these 30-plus filters include the nature of the glass, the retaining ring and the specifics of the coatings used on the glass.

It�s worth noting that ordinary window glass does a decent job of blocking ultraviolet radiation, which is why aside from possibly schvitzing from the heat, you can�t get a sunburn sitting next to a sun-drenched window. But plain glass alone cannot dampen the effects of UV radiation as thoroughly as glass with coatings designed to further block UV light. In order to block the negative effects of UV, filter manufacturers began producing filter coatings designed to reduce its negative impact on images.

The most basic of these filters is the standard UV Protective filter, which as its name implies, is designed to protect the front element of your lens while blocking the effects of low-level ultraviolet light common to outdoor picture-taking. As a rule UV filters have a warm amber cast, though most protective UVs appear colorless. A step up is a Haze 1 , which depending on the manufacturer can be also be labeled a UV 1a, UV-010 or UV(0) and blocks about 70% of the UV portion of the spectrum. Haze 1 filters also reduce the bluish tint that often rears its ugly cast to color photographs taken outdoors on bright sunny days, especially affecting color slide films.

For additional UV damping (approximately 81%) there are UV-15 filters, which in the hierarchy of UV filters reside in between the more moderate UV-16 and UV-17 filters and stronger UV-2A filters.

UV2 filters, which depending on the manufacturer are also called UV-415, UV2A and UV2B filters, are optimized for shooting at the shore or near large bodies of water, in snow or at higher altitudes where the levels of ambient UV radiation are significantly magnified. According to the specs, UV2 filters and their equivalents from competing filter manufacturers eliminate 100% of the effects of UV radiation.

Other variations of UV filters available from filter manufacturers include UV17, which eliminates approximately 97% of the ambient UV, UV-410 for high-altitude and open-water environments and UV-420, which not only blocks all UV radiation but spills slightly into the visible spectrum resulting in an overall warm tint to the photograph. Two other UV filter designations used by certain manufacturers are L37, which is designed to cut through the 370nm portion of the UV portion of the spectrum, and L39, which affects the 390nm portion of the spectrum.

Generally speaking, the heavier the filter�s UV coatings are, the warmer the overall tint of the filter will be�regardless of the manufacturer.

In addition to UV coatings, most filters also feature additional lens coatings designed to reduce lens flare and chromatic and optical aberrations. Multicoated filters are also more effective at maintaining optimal contrast and color saturation levels of the scene being recorded.

A lens is a complete optical system unto itself, consisting of multiple groups of individual elements that work as a unit to transmit a photographic image to the camera sensor (or film) with edge-to-edge sharpness and true color fidelity. Add a filter with questionable optical characteristics and you run the risk of compromising the very qualities that enable the lens perform to the best of its abilities. For this very reason one should never cut corners when purchasing filters, UV or otherwise.