This is easily the most crucial and fundamental rule of film making and also one of the most difficult to explain and comprehend. Once you get it your films will improve dramatically.
So let's say you're shooting a conversation between two of your characters. The characters are facing one another and the shot you've composed looks something like this...
Now let's says you want to get a different angle on the shot. It's the same conversation, but you want to change it up a bit. Let's say you walk around to the opposite side of your actors and shoot from there so now your shot looks like this...
Now let's say you cut these two shots together. What would your audience experience? I'll tell you, they would be watching your two actors then suddenly it would appear as though your characters swapped positions. It would be jarring, confusing and possibly nauseating. This happened because you crossed the line.
WTF is the line?
It's an imaginary line the extends straight out from your actors nose and out of the back of his head. If you are shooting your subject you should never cut from a shot on one side of the line to a shot on the other side of the line.
To explain this further let's look at the same scenario of two characters in a conversation. This time let's take a bird's eye view from above looking down...
What we have here is our two actors (A and B), our camera and the line. As long as you keep your camera on one side of the line you will not run into problems. To help you understand why this is, try to imagine yourself watching a film in which you see an actor walking, looking or talking in one direction then suddenly they are walking, looking, or talking in the opposite direction.
You may be thinking WTF, this is way to limiting. I want to shoot from both sides of the line. There's good news. You can. Here's the trick if you want to cross the line, shoot a neutral shot. A neutral shot is most commonly a shot taken on the line like this...
Another solution for crossing the line is to simply leave you camera running while you do it. If the audience sees you moving around your subject they will not be jarred when the actor is suddenly facing a different direction.
Still, I'm certain some of you are thinking that this is a stupid rule and it should be broken, after all we are shooting a zombie documentary and in the midst of a zombie apocalypse no one is going to give a rat's ass about the line. You're probably right, but I can promise you that the girl who edits that footage will do her best to make sure the footage matches.
But surely there has to be an exception.
You can use the jarring effect of jumping the line to your advantage. Here is a great example, pay close attention to what happens after about 40 seconds...
This is a clever sequence. The Gollumn character is conflicted, his personality has split and the two sides are in conflict. Crossing the line in this sequence creates the impression that there are two Gollumns. Physically there is only one, yet look at how crossing the line actually makes it appear there are two Gollumns.
That's today's lesson. For those who may have picked up this post elsewhere, it was originally posted on lostzombies.com.
If you have any questions post them in the comments or send the to me.