You may have read or heard something about Polaroid's giant 20 x 24 Land Camera. On a recent trip to New York, I had a chance to see one in action.

Shooting with the 20 x 24 is not exactly like taking snapshots with a hand-held instant camera: First of all, the camera is big -- and impressive. In the white-walled studio it stood in splendid isolation, its rich mahogany surfaces gleaming and the black bellows relaxed in soft accordion folds. It looked like a well-kept heirloom restored to museum condition: not the kind of camera you just walk up to without being introduced.

Closer inspection showed that the 20 x 24 was really a 8 x 10 studio camera blown up and modified to use a 20-inch-wide strip of Polacolor film. The camera weighs 200 pounds and has a bellows extension of five feet. Packed, it measures 25" by 41" by 59".

Despite its bulk, it can be nimble. The film plane can tilt 15 degrees and rise 18 to 95 inches. The lens can also tilt 15 degrees, rise 24 inches, swing 15 inches and shift 6 inches -- not bad for a pictorial pachyderm. The 10 lenses available range from 127 mm (five inches) up to 1200 mm (48 inches).

In fact, the 20 x 24 has done such jobs as portraying President Jimmy Carter by maestro Ansel Adams; capturing the enlarged brushstrokes of Impressionist painter Monet, and copying the 3500 B.C. Biblos death mask as well as the 3,000-carat amethyst head of the Egyptian pharoah, Ramses II.

But the interior is what makes this camera unique. It contains a giant roll of light-sensitive film, a roll of positive sheet and a magazine that holds 15 pods of chemical reagents. After the picture is taken, a button is pushed to start a motor that then processes the film by breaking one of the pods and spreading the reagent between the light-sensitive material and the positive sheet by means of a set of titanium rollers.

The finished print as it comes out of the camera is no instant beauty. In fact, it looks black, and not until 75 seconds have passed can the black be peeled off to reveal the supersize-supercolor snapshot.

By now, I'm sure you've gotten the idea that the 20 x 24 is not only a big camera but may also be a big deal -- and it is. This one is not for fun -- unless you think that $1,000 a day and $25 a print is funny.

Taking instant pictures this size is serious business, and Polaroid reserves this one for the pros. For them, the price -- which includes studio space, materials and an expert who assists -- is within reach. The unique opportunity of shooting one-to-one size imagery, the ability to correct instantly and change composition and lighting, offset the cost.

The 20 x 24s are all custom-made, and Polaroid isn't tuning up for mass production. What it's doing is giving noted photographers an opportunity to experiment with the models that do exist. Besides the one at Polaroid's 20 x 24 Studio at 20 Ames Street in Cambridge, Massachusetts, it has another on tour at the Paskarcik Studio, 1200 Broadway (at 29th Street) in New York City. More tours are planned, and you may find one of these giant cameras near you. Meanwhile, if you're in Cambridge, call 617/864-6000 (in New York 212/683-3030) for a chance to see how they are made or try your own hand at making a giant instant. Q: Is there any way to shoot color shots with fluorescent light so that the color is good instead of a sick green? And how about flash -- will that correct the color? A: There are two reddish-colored filters made that will correct the lack of red in fluorescent lighting. They are called FLD for daylight film and FLB for indoor tungsten. I've had very good color with the FLB (with some manufacturers FL-T) and Type B (tungsten) indoor Ektachrome film, but if you're only an occasional shooter you may prefer the FLD and just put that on when going indoors for the fluorescent shots.

There are many types of fluorescent lights and each takes a special filter if you want absolute color correction, but for general use the FLD or FLB or FL-T filters will give sufficient correction.

Flash can be used to correct the color balance of fluorescent-lighted scenes. In an average-size room a bounce flash will mix with the fluorescent light and correct the color. For the technique, just use the regular bounce-flash exposure and ignore the fluorescent light output. In larger rooms a straight-on flash from a distance will provide correction. When using flash-fluorescent light, slow your shutter speed so that the lighting in the room will additionally register. Q: We have an old Eastman camera that took excellent 3 1/2-by-5 7/8 pictures -- postcard size. This camera used a 122 size film, which seems to be discontinued. Do you know of any film that can be substituted? A: I called Tom Bates, Eastman technical representative, and he told me you were out of luck. Indeed, Eastman no longer spools this size film. Tom added that he has a similar model and has been able to take pictures by spooling 90-mm width film, which can be bought in 100-foot lengths. But this solution is one for experts, since you'll also need to place protective paper in back of the film and align numbers that will correspond to the original 122 film so you can tell how far to advance the roll for the next picture.