Question

how the peple sitting in a cinema hall can see the film focussed at the screen

Answer 1

A 40 to 45 degree field of view is generally though of as optimum for wide screen films with 30 degrees considered the minimum by SMPTE. Naturally there is no law against wanting to sit outside of this range.

The trick, whatever you end up preferring, is to be able to easily find the right row for your preferred angle of view. One problem is that the best time to enter the theater to get the seat you want is when the house lights are still up and there's nothing on the screen or some bad looking commercials. The problem here is that the apparent size of the screen is smaller under these conditions than it will be with all the lights off and a full screen picture.

There is an easy, but embarrassing way around this. If you extend your arm all the way out in front of you with your fingers pointing up, the width of your hand will be pretty close to 10 degrees. So start with seat where the screen is 4 to 4.5 hand widths across and wait for the movie to start. From here you can move around until the picture width seems perfect. Now see how many hand widths is takes to cover the screen.

Now whenever you go to a theater you will be able to measure the visual width of the screen and find the right row, regardless of the theater layout.

Answer 2

through projector as projector focuses the light on the white screen