Perspective and the effect focal length has on it is something many photographers don’t always seem to fully understand, at least in my experience. Often there is a belief that having a wide-ranging zoom gives you access to different perspectives, which, strictly speaking, is not the case.
Let’s start with this example of a situation we are probably all familiar with this, and is a common perspective 'problem', photographically speaking:
imagine you are trying to take a picture of a multi-story building across a city street. You probably use a wide angle lens (or the wide angle end of your zoom) and you tilt the camera upwards, to get the whole building in the composition.
In the resulting image, the building seems to lean away, because the top of the building is further away, and so appears smaller, relative to the bottom of the building which the camera is much closer to (sometimes called perspective distortion, but it's really just...well, perspective).
So lets suppose you decide to move to a more distant point-of-view. In order to keep the same or similar composition as before, you now switch to a telephoto lens. As you are now further away, the subject-to-camera distances to the top and the bottom of the building are more similar, and so the building does not appear to lean as much (or at all, if you are far enough away).
So what happens to the building now if we stay where we are, but refit our wide angle lens? Of course our composition is altered due to the increased field-of-view, and the building looks smaller in the frame. But the building still doesn't lean - because our point-of-view hasn't changed since the telephoto shot, even though we are now using the same lens as when we were close to it.
Changing lens has not altered the perspective - because we already fixed the perspective ‘distortion’ by moving further away. If we crop this image down to match the composition we took with our telephoto, both images will have identical composition and perspective, the latter being because we didn't change our point-of-view.
You can test this yourself by:
Take a picture with a wide angle lens.
Without changing position, change to a telephoto lens, or zoom in, and take another picture.
Now take the first picture and crop it to roughly match the composition in the second picture.
You will notice that the telephoto and cropped wide-angle images look the same. The relative sizes of elements of the scene and the relationships between them look exactly the same.
Below is a quick example I made using Artemis Directors Viewfinder on my phone. The first two are taken from the same spot, first simulating a wide angle lens and the second simulating a mild telephoto lens.
Wide Angle
Equivalent to 24mm lens
Telephoto
Equivalent to 75mm lens
Wide Angle Crop
A crop from the wide angle image to approximately match the telehoto shot above - notice how the relative positions and sizes of all the elements in the scene are identical to the telephoto shot.
To summarise:
Camera position relative to the scene is the only factor that determines perspective (point-of-view) i.e. relative size and position of objects in the scene. It is also one element that determines our composition.
Lens focal length is another element that determines our composition (field-of-view) i.e. what is included/excluded from the scene, but does not alter perspective.
Point 2 is why I personally prefer primes to zooms for creative work. With zooms, you can get lazy, by standing in one spot and zooming in and out to alter the composition, but may not think as much about changing your perspective.
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