To keep up with Robin Williams' improvisation on 'Mrs. Doubtfire,' 4 cameras ran all the time, and 2 million feet of film was used, says director

• Chris Columbus had to run four cameras at the same time to keep up with Robin Williams.
• All the improvisation resulted in 2 million feet of film being used to shoot the movie.

"Mrs. Doubtfire" director Chris Columbus says he made a deal with Robin Williams before making the now-classic comedy: Williams would shoot what was in the script three or four times, and then he was allowed to play.

And, boy, did he play.

Speaking to Business Insider to mark the 30th anniversary of the movie, Columbus reveals the steps he took to stay on top of Williams' outlandish improvisations.

"We would have exactly what was scripted, and then Robin would go off and it was something to behold," Columbus says.

"It got to the point that I had to shoot the entire movie with four cameras to keep up with him," the director continues. "None of us knew what he was going to say when he got going, and so I wanted a camera on the other actors to get their reactions. For Pierce Brosnan and Sally Field, it was quite difficult for them not to break character."

In the movie, Williams plays a recently divorced father who, in a desperate attempt to see his kids on a daily basis, dresses as an elderly British woman and poses as the children's nanny.

Columbus says that Williams did some form of improvisation in almost every scene in the movie, leading to 2 million feet of film being used on the shoot.

Columbus jokes that if the movie were shot today with digital cameras, Williams would never stop.

"Once we were out of film in the camera, we would say to Robin, 'We're out of film.' That happened on several occasions," the director says.

Columbus, who is also known for directing "Home Alone," says that out of all of the improvisations Williams did, two stand out as his favorites.

At the end of the movie Williams, as Mrs. Doubtfire, loses his teeth in his drink. "You can see the glee in Robin's face, he's almost smiling to himself that he came up with that," Columbus says.

And the famous pie-in-face sequence in which Williams frantically goes back and forth from his Daniel character to Mrs. Doubtfire required 18 takes.

"When he's in the bedroom putting on the Doubtfire costume, that probably was his hardest work on the film. Verbally and physically," Columbus says. "He was physically spent after doing that."

Columbus says he has over 900 boxes of footage — made up of outtakes, behind-the-scenes, and used footage — that he would like to use in a documentary that highlights Williams' genius process.

"He was in his prime at that point in his life and it was like divine inspiration," Columbus says.