Last week, my family and I went to the beach for a picnic. It was a beautiful sunny day. The sky, a deep blue, was filled with white, fluffy clouds. It was indeed a picture-perfect day.

We were not alone. Others had come to the beach for a day of fun in the sun. Many had cameras to document their outing.As a professional photographer, I'm always interested to see what type of equipment people are using, so I walked around, trying to be unobtrusive.

I was surprised to note that not one photographer was using a polarizing filter, perhaps the single most important filter in landscape photography. This filter, which ranges in price from $15 to $45 (depending on the filter diameter of your lens), can darken a blue sky and highlight white clouds. It can also make outdoor pictures look sharper because it reduces the effect of haze in a picture. And, it can also reduce glare on water, sand and leaves.

I rarely photograph a landscape without a polarizing filter. For me, this filter can make the difference between a great shot and a snap-shot.

You'll notice that I've used the word "can" and not "will" when referring to the effect of a polarizing filter. That's because a polarizing filter is not effective 100 percent of the time. Basically, it works best when the sun is off to your left or right. It will not work if you are shooting directly into the sun or if the sun is at your back.

If you were one of the people I saw at the beach who was not using a filter, and if you're really interested in getting the best possible outdoor photographs, I'd suggest investing in a polarizing filter.

If you like photographing landscapes, another useful filter is the Tiffen enhancing filter, which intensifies reds, oranges and browns. I used this filter in Monument Valley and the Grand Canyon, and was impressed with the enhanced color in my pictures.

Graduated filters also are helpful when photographng landscapes. These filters are clear on the bottom, colored on the top and come in a variety of colors. With a graduated filter, you can turn a gray sky into a blue sky and a blue sky into an orange sunset sky.

Neutral-density graduated filters are also available.