Fun with Focal Lengths
Framing a shot can be a fickle task. A photographer needs to be aware of which lens that he is using in conjunction with his vantage point and distance from the subject and arrange all the environmental elements in such a way that it makes a pleasing image. This applies to video just as much as it applies to still photography, but how is it that you choose your lens? There are so many, and they all serve specific functions! AH! PANIC!!
Have no fear! I am here to help! With THIS diagram!
Compare the shots taken with a 20mm lens and the ones that were taken using the 200mm lens, and you will see a stark contrast.
The picture that was taken at 20mm makes the model look very disproportionate, with a big head that is at a weird angle and a body that doesn't match the size of her head. In addition to the distorted features of the model herself, you can see the wall behind her is bent. The reason for this is that, because of the wide nature of a 20mm focal length, it starts to give a fisheye effect, trying to cram a lot more of an environment into the same frame size.
After about the 100mm photo, the model starts looking about the same. It's important to note though that these were probably shot at different distances to get close to the same framing in the original pictures. When the photographer was using the 50/70mm lens, the model looks natural and pleasing to the human eye because her proportions seem just right. Now look at this next picture:
Notice that the framing of the model is just about the same throughout the entire sequence. Like I mentioned before, to achieve this the photographer would need to be changing his distance from the subject, moving farther away as he increased the focal length of the lens.
The really cool part is in the background, though! Notice that, in the first photo, the background consists of a wide, sprawling landscape and the building looks very far away. However, as the photos continue to go up in focal length, the background becomes tighter and tighter. The reason for this is that, along with a higher focal length, comes a narrower field of view, so even if the subject is framed the same the picture will change lens to lens. (See field of view here.)
Application in Video
Aside from the obvious application of frame composition that relates to photography as well as filmmaking, the field of view/focal length/camera-subject distance formula can be exploited in a very unique way using motion picture. See below:
Another oldie but a goodie:
So, what is going on? It's like we are zooming in, but we aren't, and everything that should be happening isn't, and you are confused and want your mommy. It's okay, this is a completely normal reaction! This is called a dolly zoom, or a Hitchcock zoom (because like, duh). The camera crew is dollying the camera in (rolling it toward the subject on a track) and, at the same time, zooming out, so it can only be done with a variable focal length lens. This creates a scene where the subject remains the same size while the background seems to become closer or farther away. It's a pretty trippy experience, all around.
Filmmakers use this effect sparingly because it's not exactly subtle and can become annoying if overused. However, when the good guy just realized that the man he has been telling all his plans to and trusting this whole time is actually in cahoots with the baddies and is about to be thrown into near inescapable peril, a dolly zoom can really drive home the point.