UV Filters

 

In the days of film the value of placing a UV filter in front of your lens was never questioned. In addition to dampening the image-robbing effects of atmospheric ultraviolet radiation, UV filters also served to protect the front element of your lens from dust and moisture. They also repelled the inevitable smudges and scratches that over time compromise the effectiveness of the antireflective coatings that go into determining how well (or not so well) your pictures turn out. Fast-forward to the modern days of digital imaging and the big argument is: “do we still need UV filters?” The answer is an unqualified “Yes.”

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.

What is UV (ultraviolet) light?

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.

How does UV light affect photographs?

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.

A UV filter is a UV filter is a UV filter… right?

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.

What is the range of degrees of UV coatings?

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.

What are some of the attributes of optical glass?

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.

The main component of a filter is the glass which, coatings aside, is what makes one filter more desirable than another. Among the attributes one must consider when choosing filters are the thickness of the glass (as a rule, the thinner the better) and the composition and country of origin of the glass (German glass used to widely be considered superior to glass produced in Asia; this statement no longer bears any factual proof). Impurities in the glass and variations in the manufacturing process determine the overall degree of optical clarity the finished product will possess, and will affect the filter’s ability to transmit the most light and maintain optimal sharpness while reducing chromatic aberrations.

Key words to watch out for when shopping for glass filters include Water White glass, an optically pure glass that can transmit 98 to 99% of the light passing through it. Water white glass also contains lower levels of iron than standard glass, which results in whiter light transmission minus the green tint common to glass containing higher levels of iron particles.

Another noteworthy keyword is “Schott” as in Schott AG glassworks, a renowned manufacturer of fine optical glass and a major supplier of glass for Schneider-Kreuznach and Carl Zeiss, two of the finest lens manufacturers on the planet.

Are gels, polyester or resin the best filters?

In addition to the 50-plus circular glass screw-in filters we stock at B&H, UV filters are also available in the form of gelatin (gels), polyester and resin. Though more fragile and easier to scratch than glass, the paper-like thinness of gel filters make them highly desirable by photographers who depend on filters but want the least amount of image degradation. Resin filters, which are thicker and therefore less prone to damage than gels, are also considered viable alternatives to glass filters.

Gelatin filters are available in rolls for gelling lighting fixtures and windows as well as smaller square and rectangular shapes for use in screw-in filter holders from Cokin and other manufacturers.

What are the advantages and disadvantages of filter rings?

Even though filter rings have little effect on the optical properties of a filter, if you inadvertently jam a filter on your lens at an inopportune time, it can certainly rip a kink in your workflow. Filter rings, the part of the filter that screws into the threaded portion of the lens barrel and holds everything in place, are most commonly made of aluminum or brass. As for which is better, brass rings are far less apt to jam when screwing them on and off your lens, and they’re less prone to denting when dinged, which makes a filter more prone to jamming the next time you try screwing it onto your lens.

Some filters are also available with thin filter rings, which are designed to minimize the likelihood of vignetting the corners of the frame when shooting with wide-angle lenses. The only drawbacks of thin-ringed filters are that they lack female threads, making it difficult if not impossible to stack additional filters if necessary. Thin filter rings can also compromise the use of threaded lens hoods and snap-on lens caps.

What should I know about Skylight filters?

When discussing UV filters, Skylight filters inevitably enter the discussion. Skylight filters, which come in two strengths (a lighter-toned Skylight 1A and a darker-toned Skylight 1B ), have a pink tint to them, compared to the amber tonality of UV filters. This pink hue is helpful when taking color photographs as it can add warmth to the image and help to reduce the bluish cast of bright, outdoor lighting. Like UV filters, Skylight filters are used to protect the front lens surface as well as cut through haze.

Skylight filters are also preferable when shooting portraits because the pink tint can be more complementary to skin tones than the amber tonality of UV filters. It should also be noted there are Skylight filters from certain manufacturers that have warm-toned color characteristics similar to UV-2A filters from competitive manufacturers, so never assume pink means Skylight and amber means UV.