Thursday, June 1, 2006

June 2006 HelpLine

White Balance And RAW

    * Do You Need White Balance With RAW?
    * Protective Filters
    * Reboot For Performance
DPMag Published in HelpLine

Protective Filters

Q) I got into a heated discussion with a friend about whether I should use a "protective" filter on my lens or keep it bare. I won't tell you which one of us is on which side, but there's a polarizing filter riding on your answer.

Lisa D.
New York, New York

A)  For those of you not familiar with this discussion, the reasoning goes like this: You've just spent a lot of money on a lens for your camera. You should spend a little more and always keep a "protective filter"-usually a UV filter-screwed on the front of the lens. This way, if you do something that might scratch or damage your lens, the filter will take the damage. And, so it goes, the filter is a lot cheaper to replace than the lens.

At face value, that logic makes sense, but it always reminds me of one of my childhood neighbors. Whenever my friends and I went over to this neighbor's house, we always giggled as we entered the living room. While the room was nicely decorated, all of the furniture had clear plastic slipcovers.

How does a protective filter remind me of a slipcover? Just as the designer of that sofa spent time and effort to create a beautiful piece of furniture, lens manufacturers spend time and effort to create an efficient and high-quality optical system. They use exotic formulations of glass and high-tech coatings to minimize reflections, diffractions and aberrations. All of this science is working to create an ideal optical path for the light that will be traveling to your camera's image sensor.

While there are excellent UV filters, no piece of glass is perfect. Adding a filter to the front of the lens can add reflections, glare and other anomalies to the optical path. All of that can degrade your final picture. So, you could change the reasoning of the original argument to: You've spent all that money on the lens—why lessen the optical quality?

If you need to use a specific filter for a specific reason (such as a polarizing filter to remove reflections from glass or darken a sky), by all means, use it. If you shoot in a harsh environment (like a place with blowing sand), you may want to use a protective filter. But if you want to protect your lens for normal shooting, I suggest the following methods:

• Always use a lens shade to protect the front of the lens, even when you don't think you need it.

• Always use a lens cap when not shooting, and don't forget to use end caps if you take the lens off the camera.

• Follow your lens manufacturer's instructions for cleaning your lens. In particular, use a manual blower to remove dirt from the lens before using any type of cleaning system.

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