Actors in Movies Vs. Actors in Theatre

Actors are actors, right?  Well there are actually quite a few vital differences between stage actors and on-screen actors.

Stage actors obviously only have one chance to get their lines right and they also have to have a bit of an open mind in case they forget their lines and have to compromise.  They also are performing for a live audience that is far away and it is apparent in the way that they act.  They over exaggerate every movement they make and project their voices so everyone can hear.  They have to deal with a lot of things that are exaggerated, like the props and costumes that they use.  They also act differently because of the environments that they are in.  The sets for plays are obviously not as realistic and elaborate as those of films tend to be.  There are no after effects that can be used to make things look better, so the actors have to learn how to do things in certain ways ie; fight scenes.

On-screen actors are meant to seem more like real people in real situations.  (This has nothing to do with the authenticity of what the film is about.  like for sci-fi movies or fantasy films)  What I mean is, that the actors aren't necessarily performing for an audience.  They are pretending to be people who are unaware that they are being filmed.  They have many times to get their lines right because films are edited before people watch them.  Film actors do not need to be exaggerated in any way while they are acting because of the use of closeups and cinematography that can be used to creatively portray things.