Summertime means beach time, which means long, lazy days of soaking up those rays and enjoying every minute of it.

By bringing your camera to the beach, you can increase your sunnyday enjoyment; but mixing cameras and sand can spell trouble, unless you do it carefully.

Even a grain or two of sand inside a camera body can trigger a trip to the repair shop. Just one grain stuck between the gears in a dab of lubricant quickly breaks apart into several grains, which break apart into several more -- all the while spreading throughout the system and gradually wearing away delicate metal or plastic parts.

One repairman estimates that as many as many as 25 percent of the cameras he receives during the summer have problems relating to sand or dirt in the mechanism. The average cost of repair? From $55 to $95 -- barring unusual complications. That's a lot of money to pay for a little careleeness. u

The simplest way to avoid it is to leave your camera home when you hit the beach, but that would mean leaving behind all chances for those dynamite sun-and-sand shots.

The next-best way is to use an underwater camera with a hermetically sealed housing or body. You can shoot it not only near the water, but also under the water without a care in the world. If that's a little extreme, you can improvise a housing of sorts for your present camera, whether rangefinder, single-lens reflex or movie.

First, remove the camera strap. Then set the camera, lens up, in a big plastic bag (no quilting, please!) and secure the bag opening to the camera lens with a rubber band.

If the bag is large enough, it should provide ample room for manipulating the controls, focusing and firing. And when that big sandstorm blows up, the most susceptible parts of the camera will be protected. It's also good protection for shooting in the rain or on a boat where spray is a concern. g

Of course, keeping your camera in shooting shape is only half the problem. Getting high-quality results under what may often be trying conditions is far more difficult. Here are a few suggestions:

Keep camera and film out of direct sun or the high heat of a closed car, trunk or glove compartment to avoid damage and color shifts on color film. c

Use a telephoto or long zoom lens whenever possible to capture distant subjects.

To get an average exposure for your subject, do not include large areas of bright sky or light-reflecting water or sand when metering. Move in close to your subject. If that's not possible, face the subject and hold up one hand, taking a meter reading off it as though it were the subject. Set the camera accordinly, ignore the meter once you remove your hand from in front of the lens, focus on the subject and shoot.

To get a dramatic silhouette shot, position yourself so that the subject is between you and a much brighter background. Take a meter reading, set the camera accordingly (or under-expose a bit, if you like), focus and shoot.

Be patient. Don't grab the first shot that comes along; wait for the one you really want. At first sight of a photograher, many people freeze up, cluster together or just stand around. After a while, they'll forget you're there. That's the time to be ready for action; one shot can make up for a day's worth of preparation.

Q: How long should camera repairs take? Four months ago I took a Canon FTb to a local shop for repair of the lens and the exposure counter window. They said they'd send it to Canon in Chicago and repairs would take up to four weeks. The camera is still not back. The dealer said it might take six to eight months. Is this standard for Canon repairs?

A: No, it's not standard, for Canon or anyone. If you haven't received your repaired camera within six months write to the Canon repair center. Enclose a copy of this column and send a photocopy to Canon's main office (10 Nevada Drive, Lake Success, New York 11040). Perhaps it can get its Chicago repair center to expedite matters.

Q: I have a Voigtland Color Skopar Kprontor-SVS camera. How do I go about obtaining an operator's manual?

A: Instruction manuals for discontinued cameras aren't the easiest things to locate. If someone has an old manual he or she no longer needs and will send it to me, I'll forward it to you. You might try placing an ad in Shutterbug Ads, Box F, Titusville, Florida 32780. One of its readers is sure to have a manual and might be willing to photocopy it for you.

Q: I'm confused. I recently bought a filter for my Minolta XG-7. The filter instruction sheet talks about multiplying exposure by the filter factor. The camera's instruction book implies that's not necessary.Which one is correct?

A: Both are corret -- or incorrect: It depends upon your point of view. Filter factors (increases in exposure when filters are used) are necessary except when metering with a through-the-lens SLR (like your camaera) or a barrrel-mounted meter (such as many compact 35-mm non-SLRs have). In those instances, the meter automatically adjusts for the reduced light transmitted through the filter. So meter as usual and forget about the filter factor.