(note: I'm leaving a lot out of this lesson for the sake of simplicity. So if you're thinking, "Reverend Jim, sir, doesn't focal length also affect Depth of Field?" or "But, isn't the outcome of a focal length selection also dependent on the size of the film or sensor?", yes, you're correct. But those things will be addressed in a later lesson.)
Many beginning (and advanced) photographers use focal length for one thing, to get closer to the subject. But that isn't really what it's for. Let me back up a bit.
Focal length, essentially (for those of you with zoom lenses) is your zoom setting. It's telephoto vs. wide. It's a "close up" from far away, or getting in lots of stuff from close up. Most people will decide what they are taking a picture of, stand where they are, and zoom in or our until the picture fills the frame the way they want it to, and then snap the picture.
That isn't really what it is for. Sure that's a useful way to use it, if you're in a bind. But it has a much higher purpose. Let me demonstrate.
Get 10 objects roughly the same size. Place them on the floor of your living room approxamately 1 foot apart from one another. Now lay on the ground with your face right next to the first object looking down the line of other objects. Sometimes, to really see this, it helps to close one eye. Now, forget the fact that you know these objects are 1 foot apart. Look at the first 2 or 3 objects on the floor and look at how far apart they seem to be from one another. Now, look at the last 2 or 3 objects and notice how far apart they seem to be from one another. If it helps you can even hold your fingers in front of your eye to "measure" the distance between them. If you've done this right, you'll notice that the closer objects appear to be farther apart and the far away objects appear to be closer together. Now imagine if you were taking a picture of something standing next to those objects. If you were using a wide angle lens (or if you were zoomed all the way out with your zoom lens) you'd place the subject next to the first few objects (closest to you) and you'd have a picture of something standing next to some objects that were relatively far apart. If you moved the subject to the end of the line of objects, and remained in the same position, you'd have to use a telephoto lens (or zoom in) to get as "close" to your subject. However, in that case, you'd have a picture of something standing next to a bunch of objects that were relatively close together. But, you shouldn't think of it that way. Instead you should say, "I want to take a picture of this subject next to these objects. Do I want these objects to appear closer together or father apart" and choose your focal length (zoom setting) accordingly and then, and this is key, move your body to achieve the proper "close up".
Sometimes (i.e. nature photography, building photography, private detective work, concert photography) it just isn't possible to get as close to your subject as you'd like. In this case, the telephoto lens will help you get "closer" to the thing you are shooting. In other cases, you can't get far enough away (i.e. taking pictures of the inside of a room). In this case, the wide angle lens will help you get "away" from your subject. In a pinch, they can be used this way. But, you should make every effort to choose your focal length based on how you want the picture to appear, then move to accomodate that focal length only altering your choice if it isn't possible to get as close (or as far away) as you need to to use that lens.
Now for your *homework*: (yeah, yeah, I'll do it to) _Pick two subjects that can't/don't move (i.e. trees, building, telephone poles, fire hydrants, etc). They should be relatively distant from one another. Put your camera's zoom to its widest setting (or use a focal length around 35mm) and arrange the objects so that the bottom of the "left" object is in the bottom left corner of the picture and the top of the "right" object is in the top left corner. Now, put your camera's zoom to its most zoomed in settings (or use a docal length around 150mm) and move your body to arrange the objects in an identical fashion._ Now look at both photographs (feel free to post them on your website/journal and comment here with a link) and notice the distinct difference in how the images look and feel even though both of the subjects are basically in the same spot in each photograph. Notice the "other" objects in the photographs and where they've moved to and how far from one another they appear to be.
The next time your taking a picture of something, just try it. Choose your focal length first, then move your body to take the picture. Or, alternately, vow to not "zoom" in or out for a week. Pick a zoom setting and leave your camera in that setting for an entire week. Take pictures as you normally would, but move your body instead of your zoom lens to get those photographs.
