It's an important scene in the 1998 film "The Mask of Zorro": Caught stealing a crucial map, Zorro squares off against his smarmy nemesis, Capt. Harrison Love. The adversaries brandish their swords and prepare to duel.

Well, they do in the widescreen presentation of the movie. In the version that has been modified to fit a regular TV screen, Capt. Love (Matt Letscher) faces the disembodied tip of the vigilante's sword. Zorro (Antonio Banderas) is no longer in the picture.

Ever since widescreen movies became popular in the early 1950s, watching them on a regular TV set has involved a compromise. Theater screens have different proportions than do TV screens.

It's an issue that has become more visible as DVDs, most of which have widescreen presentations, spread to the masses.

Full-screen-only DVDs have begun to proliferate, with stores such as Wal-Mart catering to uninformed consumers by using stickers on the package that proclaim "No black bars!"

Basically, when a widescreen movie is transferred for viewing on a regular TV screen, it's presented one of two ways:

The image retains its theatrical proportions, leaving black space (not "bars") above and below but showing the movie the way it was intended to be seen. This is sometimes called a "letterbox" presentation.

Or, the image is modified from its original presentation to fit the screen from top to bottom and side to side, losing part of the picture in the process. This is called a pan-and-scan presentation.

"If you don't see a widescreen movie in a widescreen format, you're missing a chunk of the movie. It's as simple as that," said Leonard Maltin, film historian, critic and DVD producer. "That particular chunk might be an actor or a group of actors; it could be the second participant in a two-person conversation; it could be a significant piece of action.

"There are really creative directors and cinematographers, and even art directors, who like to use the widescreen frame; otherwise, why bother shooting it that way?" he added. "When they carefully compose those shots, any variation on that is going to destroy what they did."

John Carpenter is one of those filmmakers. The director of films such as "Halloween" and "Starman" says he spent extra money for the widest presentations on even his lowest-budget movies because he felt it made a difference.

Asked what he thought of pan-and-scan home versions of movies, he said, "It makes me sick to my stomach."

He cited one of his favorite films, "Once Upon a Time in the West," as an example.

"You can't watch that thing in a pan-and-scan version," he said. "It's an atrocity."