Polaroid's instant snaps, those party chronicles that darken from anemia to deepest blush in 60 seconds, are elevated to an art form in two current shows. Focusing on works made with Dr. Edwin H. Land's 20i x 24i camera, the prints are grand in scale, if not always in subject matter.

"20x24 Polaroid" at the National Academy of Sciences features 32 large-scale works. "Large" means 480 square inches of film exposed with each click of the shutter. Besides their scale and color, it's the intricate detail that makes these works compelling. Andy Warhol's head fills a whole sheet, every crease a crater.

The process is a throwback to an earlier stage of photographic history. The camera weighs in at 200 pounds, a sleek refinement on the original 800. It's still a piece of work with old-fashioned bellows that extend to seven feet, a mahogany-and-brass frame that's five feet high, three feet wide. The basic difference between hand-held party Polaroids and the 20i x 24i contraption: the latter requires a motor to drive the processing rollers, rather than cranking through the light-sensitive sheets by hand.

The show's subjects range from stately to absurd. Portraits of Buckminster Fuller and artist Lotte Jacobi show every dignified hair and wrinkle. Still lifes and music/word collages have a crispness that threatens to outdo the real thing. Sandi Fellman documented lush, satiny textures and leggy subjects. John Pfahl manipulated perspective to turn ovals into circles, rectangles into trapezoids. Ansel Adams used a Polaroid to capture a spectacular panorama of trees and mountain peaks (untitled, 1981). Less inspiring but more provocative is William Wegman's "Ray and Mrs. Luebner in Bed," a spoofing portrait of two dogs tucked in people-like, with a deer peeking through the window of a rustic cabin.

Across town, Wegman's mischief is featured at 406 Seventh Street NW. The McIntosh/Drysdale Gallery shows him to be master of the bizarre -- if sometimes a cruel master.

Wegman used the 20i x 24i Polaroid in collaboration with his best friend, a Weimaraner named Man Ray, to achieve large-scale weirdness. Humor, shock value and embarrassment to animals play a part: Ray appears in high heels and feathers, as a bug-eyed frog in scuba flippers on cut-outs of lily pads beneath a fern, with leopard stripes, being "dusted" or pelted with paper shreds. Call it abusive or call it art, these 11 huge color photographs display a twisted comic sense. They sell for $2,500 each, $4,500 for a diptych.

Scientists and men of commerce approach equal billing with the artists in these shows; it's only unfortunate that the machinery isn't on display.

NATIONAL ACADEMY OF SCIENCES -- "20x24 Polaroid," through April 30. Call ahead for weekend admittance, 334-2436. Monday through Friday, 9 to 5.

McINTOSH/DRYSDALE -- William Wegman, "Polaroids" through April 1 at 406 Seventh Street NW.