Working with Perspective, Subject Distance and Focal Length
Common sense is that wide angle lenses exaggerate perspective while telephoto lenses compress it. But common sense is wrong. In reality, perspective depends solely on relative subject distance. Let's look at how we can best to use this when framing and composing images.
The easy approach to composition is to walk around until you find something that interests you and take a picture of it. Nothing fancy. You see something you like, stop in your tracks and whip out your camera. With zoom lens attached, you frame your subject to fill the frame as desired and press the shutter release. You're done. Time to move on and find something else to shoot. But changing focal length makes everything in the frame get bigger or smaller in unison.
Before you reach for the zoom take a few moments to consider where you are shooting from. Take a step forward and your subject will appear larger since it is closer to you. Take a step back and it gets smaller. But other objects in the frame won't necessarily change in size proportionally since their distance from you isn't the same as that of your subject. An object that is twice as far away as another identical object will appear half its size. If you get closer to one though, your relative distance to the other will change, causing their apparent sizes in relation to each other to also change.
That being the case, position yourself where you need to be to achieve the perspective you are after before considering lens choice. Make that perspective something interesting — whatever you need to accentuate your subject. If you want your subject to seem larger than life, get close to it. If you want to make it seem more to be stacked up right against the background, shoot from much farther away.
Once you have established where you need to be, then consider what lens you will need to use. Focal length won't affect perspective. Zooming in and out makes everything appear bigger or smaller together. You can now confidently frame your subject safe in knowing that the perspective you decided on will remain as you wanted it.
Once both your position relative to your subject and your lens selection have been set, you are ready to take that picture. And I promise you it will come out better than the one you might have taken when your subject first caught your eye and made you stop.