Before the coming of computers, achieving special effects in motion pictures was, in a way, much more complicated than it is now.

In the "olden" days, one of the most popular (and time-consuming) methods of special effects was done through stop-motion photography. If you wanted a dinosaur to move on screen, you photographed a small model in various poses one frame at a time.One of the best at stop-motion was Ray Harryhausen, who became interested in doing special effects when, as a youngster, he first saw "King Kong." That was the 1933 original, which showcased the work of the father of stop-motion photography, Willis O'Brien.

Harryhausen saw his dream come true and to his delight, his first movie assignment was to assist O'Brien on "Mighty Joe Young" in 1949. Four years later, Harryhausen went solo as he made "The Beast from 20,000 Fathoms" come alive for Warner Bros.

During the next three decades, his work was showcased in 14 films, many of them devoted to ancient legends. Admittedly, these kind of films are not for everyone, but if you love adventure and get a thrill out of seeing strange creatures come to life, then you'll enjoy Harryhausen's wondrous work.

Most are available on video and those that are not frequently turn up on television:

THE BEAST FROM 20,000 FATHOMS (1953). A prehistoric monster is unleashed by atomic blasts in the Arctic and eventually wreaks havoc in New York City. Black and white. Not on video.

IT CAME FROM BENEATH THE SEA (1955). This time San Francisco is the target with a giant octopus doing the damage. Black and white. Goodtimes, $14.95.

EARTH VS. THE FLYING SAUCERS (1956). Aliens have their sights set on conquering the world. Spectacular climax as saucers seemingly destroy every landmark in Washington, D.C. Black and white. RCA/Columbia, $14.95.

20 MILLION MILES TO EARTH (1957). A spaceship from Venuscrash-lands and unleashes a strange creature that runs amok in Rome. Black and white. RCA/ Columbia, $19.95.

THE 7TH VOYAGE OF SINBAD (1958). Sinbad saves a princess from an evil magician and encounters numerous weird beings, including a vicious cyclops, along the way. One of Harryhausen's best. RCA/Columbia, $19.95.

THE THREE WORLDS OF GULLIVER (1960). A reworking of the classic story. Not bad. RCA/Columbia, $69.95.

MYSTERIOUS ISLAND (1961). Based on Jules Verne's story with the addition of some good Harryhausen monsters. RCA/Columbia, $19.95.

JASON AND THE ARGONAUTS (1963). Another magnificent showcase of Harryhausen effects as Jason searches for the golden fleece. The climactic battle with an army of skeletons is downright breathtaking. RCA/Columbia, $19.95.

FIRST MEN IN THE MOON (1964). Based on a top-notch Jules Verne story. Men land on the moon in the 1960s and discover an old British flag there. For once, Harryhausen's work takes a backseat to a very entertaining production. RCA/Columbia, $19.95.

ONE MILLION YEARS B.C. (1966). Except for Harryhausen's brief effects early in the film, this one is a dud that seems to go on forever. Not on video.

VALLEY OF GWANGI (1969). In turn-of-the-century Mexico, cowboys discover a land that time forgot. They capture a dinosaur for a carnival. Naturally, he escapes, much to the horror of Mexico City's citizens. Entertaining fun. Not on video.

THE GOLDEN VOYAGE OF SINBAD (1974). Sinbad again encounters an evil magician and a bevy of strange creatures. RCA/Columbia, $19.95.

SINBAD AND THE EYE OF THE TIGER (1977). Sinbad races a wicked witch to a hidden treasure. The Sinbad formula was beginning to wear thin with this one. RCA/Columbia, $69.95.

CLASH OF THE TITANS (1981). Harry Hamlin of "L.A. Law" is the hero in this story based on Greek mythology. There are some good special effects, but the film's human characters have little to offer. MGM/UA, $79.95.VIDEO QUESTION

Q: Can you tell me if "Oh, What a Lovely War!" is on videotape? Video-store people aren't much help.

A: I get many questions like this on movie availability, but answering them here is not practical - usually it's of interest only to the questioner. But I can tell you where to look. Your local library probably has the two best reference books in the field: "The Video Source Book" (Gale Research) and "Variety's Complete Home Video Directory" (Bowker). I looked up your title - it's not on tape. - Andy Wickstrom (Knight-Ridder)NEW VIDEOS

AFTER MIDNIGHT - Prof. Edward Derek (Ramy Zada) teaches in his Psychology of Fear class that "to understand fear, you have to experience fear." So he adopts the use of audio-visual aids (nothing like the glint of a sharpened ax or the click of a loaded gun to get the point across to a class of somnolent co-eds). For some reason, the college cancels the professor's class. No problem; the professor merely suggests to his students that they continue his fearsome lectures at his house - say, after midnight. This being a movie, the kids think that's a swell idea. But they don't learn what "real" fear is until one student comes to class one night with an ax of his own, seeking revenge against Prof. Derek - or, perhaps, just as an extra-credit project to make up for that midterm he slept through. CBS/Fox. $89.95. - Tom Maurstad (Dallas Morning News)

EWOKS: THE BATTLE FOR ENDOR - This is a video that can get on an adult's nerves in a hurry. Terminal cuteness is not a virtue. This live-action TV-movie from George Lucas chronicles the plight of an orphan and her Ewok friend who escape from evil King Terak and are befriended by a kindly woodsman (Wilford Brimley). There is an arsenal of special effects certain to thrill youngsters, and most kids age 4 and up will find something of value in this tale of friendship and right and wrong. But you'd think a credible plot was as important as morality, and this shallow excursion just doesn't have one. But parents can strike a compromise: rent this tape for the kids then do some yard work until its over. MGM/UA. 98 minutes. - Mike Pearson (Scripps Howard)

SCOOBY & THE RELUCTANT WEREWOLF - One of two feature-length videos that has been released in time for Halloween featuring TV's Scooby Doo and his cartoon sidekicks. Scooby Doo is this year's Safety and Goodwill Delegate for the U.S. Committee for UNICEF's National UNICEF Day campaign. Portions of the proceeds from the videos will be donated to the organization. If your children are fans of the Scooby Doo show, they'll probably enjoy the video, although they may not go the distance at 95 minutes as Scooby-Doo and Shaggy are pitted in a car race against ghoulish monsters to save Shaggy from Dracula's spell. Hanna Barbera. VHS-Beta. $29.95. - Mike Pearson (Scripps Howard)