Pro Techniques

UV and Skylight filters—do you really need one on every lens? The guy at the camera store told you that a filter is “cheap insurance against fingerprints and expensive repairs” but was he really looking out for your best interests? Should “protective filter” be spelled:
P-R-O-F-I-T? And darn it, how come some filters cost nearly as much as a lens while others are just a few bucks?

Let’s start with the fundamentals. To begin with, a filter is a lens, albeit a simple one. Ideally it will allow about 98 percent of the light to pass through. The other 2 or 3 percent is either reflected or absorbed. No light waves should be refracted, otherwise the image that they form will be distorted. This is a perfect world scenario, of course—reality can be less cooperative.

The true purpose of an Ultraviolet (UV) or Skylight (1A or 1B) filter is to absorb a tiny amount of blue light. Blue light waves, being the shortest in the visible spectrum, are prone to scatter more readily than other colors. This creates what we describe as “atmospheric haze.” In other words, haze equals scattered blue light. Skeet shooters know this, so they wear yellow glasses. The glasses also protect their eyes, a fact that should not be overlooked when you decide whether or not your lens needs a filter.

High-quality filters are thin, multi-coated, and plano-parallel. Thin glass refracts less (all else being equal) and thin filters assembled in appropriately thin mounts are less likely to cause vignetting with wide-angle lenses. Multi-coating improves light transmission—which is another way of say that it reduces reflection.

Plano-parallel simply means that the filter is of uniform thickness and that the top and bottom surfaces are perfectly flat and the same distance apart at every point. I knew a guy who—for years—referred to this characteristic as “plain old parallel.” As a matter of fact, he had the IQ of a fish stick, but he was sly enough to sell tons of unnecessary “protective” filters to unsuspecting camera purchasers.

Filters are extraordinarily useful accessories. You do need filters, but you do not need one on every lens. This assertion will make me unpopular with legions of camera store salespeople who have been instructed to sell filters one-to-one with lenses, but they simply are not necessary. Store clerks will tell you horror stories of lenses that were “saved” from total destruction by a filter, but that notion defies logic. Indeed, a glass filter can protect the front lens element from fingerprints, dust, and moisture, but any impact sufficient to damage a filter is likely to be transferred to the lens anyway, spreading the damage the same way an earthquake does—by intense vibration.

As a matter of fact, in all my years I have seen many, many more lenses that were damaged by filters that either got stuck because they were screwed on too tight, or were cross-threaded and could not be removed without a pipe wrench. Cheap filters can even distort your photos, and some cheap filters can rob you of noticeable sharpness.

Always buy the highest quality filters you can afford. Use thin, multi-coated UV and 1A filters for the purpose they are intended—to reduce atmospheric haze and to knock down the excess blue on a cloudless day. Use them to protect your lens when you know you’ll encounter foul weather or kids with grimy fingers. But don’t waste your money on a “protective” filter for every lens.

You can read Jon Sienkiewicz’s Blog at: www.shutterbug.com.