Under The Hood - Zoom
I think it is incredibly unlikely I will ever, ever, ever use a zoom in any film I am directing. Ever.
Sure - I may use a lens capable of zooming, a zoom lens, but it will never zoom during a shot. And this is with very good reason, which I'm going to explain - once I've explained exactly what a zoom lens is.
Most lenses are called prime lenses. The thing with prime lenses is that they're fixed. They have fixed focal lengths and therefore, offer a fixed depth of field and field of view. Zoom lenses do not - you can alter the depth of field and field of view on a zoom lens. If you do this during a shot, if the change is recorded, that's the effect we know as zooming. You know the shots where the iamge suddenly gets sort of bigger/closer - or, most accurately, zoomed in.
Almost all camcorder lenses are zoom lenses.
So, with a wide angle prime lens, you have a wide field of view and a deeper depth of field. With a long lens (aka telephoto lens) you have a narrow field of view and a shallower depth of field. A zoom lens is variable so it can move between wider and narrower fields of view, the depth of field changing accordingly.
Imagine a camera on a tripod in a studio. A fixed distance away, not moving, is a mannequin. Through the wide angle lens, the wide field of view shows more of the room from left to right than the long lens would. The long lens, however, has a more narrow field of view, showing less of the room left to right. Because the width of the image doesn't change the effect is this: you effectively appear to be nearer to the mannequin when using the long lens.
If you have a zoom lens on the camera and start at the 'widest' setting the image will be comparable to that of a wider prime lens. If you then use the zoom control to steadily zoom in, altering the angle of view and depth of field, gradually altering the charavteristics of the lens from those of the wider primes to the longer primes, what happens is the area of the mannequin image in the centre of the picture gets larger and larger, while more and more of the image moves out of the edge of frame. Zoom in enough and you might just be staring at a desing on the mannequin's shirt, instead of the whole thing, and the big room around it.
If you instead had only the wide prime lens but mounted the camera on a dolly track and moved towards the mannequin, do you think the same effects could be acheived?
Well, something a wee bit similar would happen. But, in fact, it's the differences that are very, very important.
Go find a nice small prop that you can stand on top of your computer monitor/desk/DVD shelf. Anything you can put anywhere, but something small-ish and the closer to eye-level the better. For the purposes of this experiment, your eye is going to be playing the part of the camera.
So, say you've stood up a little hula-Elvis toy on top of your monitor. Ideally, there's a patterned something on the wall a little way behind - a poster say, or some pictures of mummy. Get your eye-camera level with The King. Get a good few feet back. Take a good look at the prop. See how Elvis hulas. And now, slowly, steadily move your head forwards. Track in, straight at Elvis. Keep level with him.
Things to note: yes, Elvis takes up more and more of your field of vision the closer you get and, actually, he's also obscuring more and more of your poster/your momma as you do so. We're talking about perspective, basically. That's what we're seeing here: shifts in perspective.
As the position of the eye moves, the perspective in the image seen changes. This is just the same with a camera.
Now, here's an experiment you can't do. Keep your head a fixed distance from Elvis and, instead of moving forward, just zoom in. Can't do it, can you? The human eye has no zoom capability. If you're on the beach one hundred feet away from somebody who's doing a real good job of modelling their swimwear, I'm sorry - you're going to have to get closer for a better look.
But that's not true with a zoom lens. So there is a very, very important difference between a real eye and a fake zoom lens one, as attached to a camera.
If you have a camcorder, experiment with it. Stand GI Joe on your cluttered desk and record two different shots. In one, leave the camera in a fixed position and zoom in on GI Joe's face. In the other, move the camera along the desk, straight at him.
The basic difference will be clear: when you move the camera, perspective alters, the sense of approaching Joe's handsome visage is in every frame; when you don't move the camera, the mechanical sense you get is of the image expanding, the centre getting bigger and bigger while the outside goes out of shot.
Zooms necessarily give an image a very flat quality. They do not create any change in perspective. And they act unlike the human eye.
We have no direct, real-life experience that is like the effect we see when a shot zooms in at all. We only know what zooming in is like from shots that zoom in, or from using zooming binoculars, or a variable telescope or similar. A shot that tracks forwards (as per the other alternative in each of our experiments) is a very typical experience for us. Every time we move around we encounter this. This is the way we see the world.
I'm not done with zoom lenses yet, trust me. This was just the foundation, so everybody can follow the next installments.
The next Under the Hood is going to be about jump cuts and zoom lenses. Basically, the problem with one is rooted in the same thing as the problem with the other. So, after I explain jump cutting a little, we can really get down to why zooming in - or indeed out - is a very bad idea. And then we'll look at when it wasn't such a bad idea at all, why this is, and what the difference was.
And then, two examples from two much loved and very famous films, one by Hitchcock and the other by Spielberg. One is going to be used as an example of good filmmaking - the other as an example of bad filmmaking. I won't tell you which is which just yet.
More soon.
