Whether you take a vacation elsewhere or stay home this year, it's outdoor time for you and your camera. The picnic, the ballgame, hike or cookout, sandcastle-building by the sea -- all are outdoor opportunities for picture-taking by natural light. But because action calls for a quick eye and a quick trigger finger, you'll need a fast film to keep up with your subject.

If it's a ballgame you're shooting, load up with fast color film (ASA 400) and set your shutter at 1/1,000th of a second to stop movement at f/8 to f/11 in bright sun. Practice shooting action by focusing on the base in baseball or softball and catching the peak as the runner is taggered out or slides in safe. Try for the big swing of the batter or the leap of the outfielder.

If you have a telephoto lens, first focus on your subject, then wait for the right action. Click when it happens in your lens. And don't forget the friends and action on the sidelines. Turn your camera around periodically, to catch a cheering fan, or someone laughing. If you get involved, you'll find that playing along with your camera can be as much fun as the game itself.

Picnics and outdoor barbecues can provide the kind of fun pictures that albums are made of. Here again, use a fast film and a fast shutter speed. To avoid having people posing for you, or being self-conscious about your shooting, stay in one place. Choose a spot from where you can fill your frame with the action, and keep looking through your lens without shooting. Soon people around you will forget about you and you can click away at unguarded moments. It helps to have a long lens, but even an 88-mm or a 105-mm will give you a large-enough image from a fair distance.

The trick to catching motion is to click when a person is at the height of his or her action, such as a ball player in mid-air, a cheerleader suspended at the height of her leap, someone drinking a foaming bottle of beer, or a child wrestling with a huge barbecued rib. This type of picture implies action because obviously the subject couldn't hold such a pose and therefore he or she must be in motion.

If you're along the seashore, trying for a summer mood with the kids building a sandcastle in the foreground and the shimmering water in the background, don't forget to measure your exposure by the kids, not by the background.

To do this, this you have an SLR with manual controls or override, point the lens at your subject without including the background and make the adjustments for the exposure. Then, move back and return to your original composition. The light or needle inside your light meter will jump, of course, but ignore it and you'll have both your subject and the background recognizable. Of course, it you are trying for a silhouette shot, by all means expose for the water or the sand. In that case you will have the background correct and your foreground subject dark or black, in outline.

The same treatment can be used for those romantic summer evenings when the sun seems to take forever to set and the sky turns a deeper and deeper red. If you want a friend recognizable in the foreground, expose first for him or her, and then let the rest of the scene come into your picture. On the other hand, if you want a pair of lovers silhouetted against the setting sun, go for the sun.

And what can you do about those rainy days, when it seems that your vacation is totally spoiled? Take an umbrella with you and go picture-hunting. Cover up your camera bag with a platic bag, but when you're ready to shoot, protect the camera with the overhead umbrella only. Trying to shoot pictures through a lens that's stuck in a plastic bag will only give you blurred images.

If you want some unusual effects, don't be afraid to take your camera out in the rain -- not into pouring rain, but wait till it looks like it's clearing and the sun is trying to break through the clouds. It helps to have a friend along to hold the umbrella overhead in a drizzle, but if you're on your own, here's a trick I've used many times. Stick the handle of the umbrella into your collar at the back of your neck. Now take the camera strap and wind it around your neck, including in it the umbrella handle. Pull the strap tight in front, so it presses the handle against your head, and you've got now both hands free to hold the camera.

Look for relected images in puddles. Notice the raindrops on leaves and flowers and move in close for a backlighted shot that will make the drops glisten like diamonds. You can also ask members of your family to dress in brightly colored raingear to accompany you on your photographic foray. In the diffused light of the after-rain, you can get some wonderful portraits of friends and loved ones. WHAT'S NEW? For the first time since Carousel slide projectors came on the scene in the early '60s, Kodak has come up with a new idea. Several of its new projectors now will come equipped with their own screens. The "Slide-Scan" screen is built-in and allows the slides to be viewed without having to set up a cumbersome screen or clear a wall. Other improvements on the seven new projectors Kodak is bringing out are an additional 16-degree tilt and illuminated side panels so the projectionist can see in the dark and a Carousel tray that can be removed whether the machine is on or off. Q&A&Q&A&Q&A&Q&A&Q&A&Q&A&Q&A Q --Could you please give me some guidelines as to what to look for when purchasing a black-and-white enlarger? I'm looking for one in the $100-to-$200 range. A -- If i were looking for a good enlarger in that price range I would start by searching the want ads and asking around the camera shops for used eqipment. It's surprising what you can pick up in the way of darkroom bargains from disillusioned camera buffs who, after all, decide to have the pro lab handle it.

There are guidelines as to what to look for in an enlarger. First off, remember that you can use a color enlarger to make black-and-white as well -- so if a bargain comes your way in color grab it.

Enlargers are of two basic kinds -- those with an indirect light source, so the bulb light is different through a ground glass; and condenser types that concentrate the image. The condenser types give a much sharper picture but the diffuser enlargers erase the scratches on the negative and give a softer, more portrait-like effect.

It's important that the lighting be evenly projected. A good way to check this is to raise the enlarger and project the entire image frame onto a piece of white cardboard and see if the lighting is even.

An equally important part of the enlarger is the lens. The best way to test the resolving power is to actually make a print at the greatest enlargement using a negative that you know is sharp. If you have the chance to compare several lenses you will quickly see the difference.

The general condition of the equipment especially if used, is important.

First, test for rigidity by running the enlarger up and down the column and then locking it in place to see if the head starts to waver under light pressure.

Next examine the condensers to see if they are scratched (or check the ground glass in the diffusion types).

A final consideration is to decide just how big your blowups will be, for that, too, will determine your price range. If 8 x 10 is the biggest you'll go, there are quite a few new ones like the Bogen series that will do a good job within your budget. Q: I have a Teleflash and a Strobo Unit II I wish to sell, and I wonder if you could tell me where I could sell them and what they are worth. Both are in excellent shape. A: Without a brand name (the manufacturer), I'm afraid I can't help. But you should be able to get a fair price by advertising "for best offer" through Shutterbug Ads (see address above). Q: For Christmas 1979, I gave my husband a Petri 35-mm camera. This year I tried finding some lenses for it but couldn't. Would you know what other camera parts are interchangeable with the Petri? Or is there a catalogue that I might write for? A: You're having trouble because Petri is not one of the better-selling cameras in the U.S. However, Petri cameras used the universal screw-mount lens system, so you should have no trouble finding lenses to fit it. At one time, screw-mount lenses were the most widely available in the world, and there are still plenty around. Check with your favorite photo dealer in finding the lenses you want.