There are huge differences between acting for the stage and acting for the screen. As an actor who grew up performing on the stage and then making my professional debut in musical theatre I was more happy with a step ball change than ‘finding my marks’, and happier projecting for the gods than internalising for the camera. Nearly all of my acting work nowadays is on screen, it is a path I am very happy to tread and over the years I have found my feet, my rhythm and my technique.
Technically there is a vast difference in the acting style you will need to use in front of the camera and these are things which you must learn, practise and develop. The new book by Bill Britten From Stage to Screen: A Theatre Actor’s Guide to Working on Camera is a terrific help for any stage actor who is making the move to screen acting.
I also found the following question asked on Quora and thought I would share the answers with you here as they really encapsulate some of the big differences which you will have to deal with when you transfer your craft from the stage to the screen.