Many photographers, even some fairly advanced amateurs, misunderstand how to properly employ lenses of different focal lengths. Although selecting a lens isn't really a step-by-step process, for purposes of keeping everything organized and showing you how to evaluate a scene, that's how it will be presented here. This tutorial will explain the reasoning behind choosing a particular lens, and highlight how considering the angle of view can lead to a fantastic photograph.
When deciding whether to "go wide" (zoom out) or to zoom in, most people use reasoning something along these lines:
1. I'm shooting in a confined area and the only way to get my entire subject within the frame is to zoom wide.
2. or... I'm far away from my subject and can't get closer so the only way to make my subject more prominent in the frame is to zoom in.
Neither of these lines of reasoning is wrong. Their problem comes from the fact that both rely on making the most of limitations imposed on you by outside factors.
When there are no limitations - i.e. you can "zoom with your feet" and move closer or farther away - many casual photographers fall into the habit of just grabbing the shot from wherever they happen to be standing.
This is one of the main reasons why so many people are unhappy with their snapshots.
It's time to begin making new distinctions about what different lenses (or different zoom lengths) will do. Rather than thinking in terms of magnification, which is essentially what the reasoning in Step 1 does, it's better to think in terms of angle of view. That is how more advanced photographers do it.
There is an added benefit to this line of thinking. Magnification is only partly a function of lens selection; it's also partly a function of sensor size. (You may have heard or read about "crop factor".) So a 100mm lens will give two different magnifications on two different cameras with different sensor sizes. However the angle of view never changes.
Let's start with the assumption that you want your subject to be prominent in the image frame (I cannot even think of a truly impactful photo in which the subject isn't prominent in the frame.) That doesn't mean that your subject has to fill the frame, but it does mean that your subject shouldn't be just a tiny dot hidden in a jumble of background garbage.
Now let's look at a series of photos showing the same subject, shot in the same setting, using different lenses. You'll notice that the subject occupies approximately the same percentage of the frame and is in approximately the same location for each shot.
So here we have a girl, standing 12 feet (3.7 meters) in front of the background. Neither the subject nor the background will be moved or changed in any way for the series of shots we are about to review. The only things that will change are the distance between the photographer and subject, and the lens used.
First we see the subject with a wide angle (14mm) lens which covers an angle of view of 64.4 degrees. The camera was 3 feet (0.9 meters) from the subject. Note how much of the background is visible here.
When you are photographing a subject and the background is attractive or important or somehow adds to the shot you are trying to take, a wider angle lens combined with getting closer to your subject may be just the ticket.
Here we have the same subject and setting only this was taken with a more normal length (50mm) lens which covers an angle of view of 19.6 degrees. The camera was 9 feet (2.7 meters) from the subject.
Note that the subject occupies about the same percentage of the frame and the frame itself is the same size but look at the difference in how much of the background is visible. No trickery was involved here, it's just that the narrower angle of view of the lens used caused the camera to not see as far out to the sides.
In order to get the subject the same size in the frame using a longer focal length lens, I had to "zoom with my feet" and move back. In this case, from 3 feet (0.9 meters) away to 9 feet (2.7 meters) away. Notice that this will be a recurring theme for the rest of this series. Each time I change the focal length of the lens, I also zoom with my feet to change the camera-to-subject distance in order to keep the subject occupying the same size within the image frame.
Now our same subject and setting was shot with a modest telephoto (150mm) lens which covers an angle of view of 6.7 degrees. The camera was 22 feet (6.7 meters) from the subject.
Once again we see a pretty significant change in the background.
Here our same subject and setting was shot with a long telephoto (300mm) lens which covers an angle of view of 3.4 degrees. The camera was 43 feet (13.1 meters) from the subject.
Note how, with each increase in focal length, our angle of view becomes progressively narrower. This naturally restricts how much of the background is visible in each shot. So to hide an unattractive background, one trick to use is to step back and zoom in or use a longer lens. The narrower angle of view will limit how much of the background you can see behind your subject.
You may also have noticed that the difference between the last two shots was not as dramatic as in the first three. First we went from an angle of view of 64.4 degrees to an angle of view of 19.6 degrees, a decrease of around 70%. Then we went from 19.6 degrees to 6.7 degrees, a further decrease of around 66%. For the last shot we went from 6.7 degrees to 3.4 degrees, a somewhat more incremental decrease of less than 50%.
It's not important to memorize angles of view (I had to look mine up when writing this!) What is important is that you have a general sense of the role that angle of view plays in the final appearance of an image and how much your camera will see with different lenses or different zoom lengths.
Now let's look at this a different way. Suppose your subject is the background and you want to step back and zoom wide to get the best view of it.
In this instance, what you want is to fill the foreground with something that will keep your shot from looking empty and yet won't compete too much with the real subject.
Here, an autumn leaf placed on the large rock in the foreground adds a tiny spot of bold color to an otherwise neutral looking landscape. Despite its small size, it fills the frame in terms of capturing a viewer's attention and yet, the waterfall in the background is still clearly the primary subject.
Some people like to take close-up or macro shots.
Close-up or macro refers to the distance between the subject and the camera. There are macro lenses of all different focal lengths, though there tend to be fewer wide angle macro lenses simply because the wider angle of view doesn't fit with what most people want in a close-up photo.
So next time you are taking a picture, try thinking in terms of how wide an angle of view you want to capture. It's a fairly simple concept to understand, but can lead to a more appropriate lens choice, and a photograph that you're far happier with.