Q. I am interested in buying a pair of binoculars. I have never owned a pair, but since I'm traveling more these days, I think binoculars would be fun to have.

The numbers confuse me. I don't know the difference betwen 7x35s and 10x50s. I assume that the 10x50s are more powerful.

Do you use binoculars, and can you give me any information on this subject?

A. Over the years, I have owned, traded and sold various binoculars. I've had some experience with Nikon, Bausch and Lomb, Sharp and Pentax.

But after this question arrived, I called my friends at Pentax to make sure my information was current. The material they sent shows that while the products and optics have improved over the years, the basic concepts of binocular use remain nearly the same.

The first thing to consider in buying your new binocs, is what you want to do with them. Many binoculars are designed for what the manufacturers call "general use," which I like to think of as things that are family-oriented. Such things as going to a football game, at school or at RFK stadium; viewing the foliage on Skyline Drive; or to take sailing or on vacation. Sometimes binoculars are great just to see what's going on down the street.

If you plan a specialty use, such as birdwatching, wildlife observation, closeups during outdoor sports, horse racing, or even night sky watching, you'll have to think along slightly different lines.

Here, with assistance from the Pentax folks, is a short primer on binoculars.

Model description: This can tell you a great deal about a pair of binoculars. For example, let's say you're looking at a pair designated 7x35BWCF. The "B" means that the binocs are of an American, single piece design. The "W" means wide-angle capability and an image magnification suitable for general use. "CF" means center focusing.

Magnification: The first number, "7" in this case, is the magnifying power. 7x means that the image seen through the binoculars appears seven times larger than seen with the unaided eye. Usually magnification from 6 to 9 is best suited for most normal situations.

Diameter of the front lens: The next number, "35" in our example, stands for the diameter of the front (objective) lens. This is the number that determines how well the binoculars "see" in low light, haze or fog.

By dividing the number (35) by the magnification (7) and multiplying the result by itself (5x5), you get a number representing the binoculars' Relative Brightness. The higher the Relative Brightness Rating (RBR),, the better the low-light capabilities of the binoculars.

Zooms: Zoom binoculars will have two magnification numbers, for example 6-15x35zcf. This means that you can choose the magnification you want at a given time. This is achieved with a finger-tip control lever or with a tiny, battery-operated motor. Be careful as you examine zooms. In many cases, the objective (front) lens number is small and the brightness rating is low. This can cause problems in low light.

Now, to apply all this.

Don't rush out and buy the highest magnification you can find. If you go above 9 magnification, your binocs will be hard to hand hold and you'll probably need a tripod to support them. In some situations you'll need a tripod even for 9x. If you're going to be using your binocs almost exclusively in the daytime, don't worry as much about the Relative Brightness Rating; if you're going to be using them at dusk, dawn or night, give up some of the magnification to get a higher RBR.

When you're shopping, try out as many different kinds of binoculars as you can. You'll find various shapes and construction, including the American-style single-piece body and the German style multi-piece body. There will be several methods of focusing, including center focus and individual eye focusing.

One last thing: If you use glasses, wear them when you test and use your binoculars.

Remember, binoculars, like cameras, are an investment. You have to pick the pair that suit you best.

Carl Kramer, former director of photography for The Washington Post, will try to answer your photography questions in his column, but cannot reply individually. Send your questions to: Carl Kramer, c/o Weekend, The Washington Post, 1150 15th Street NW, Washington DC 20071.