The question of what effect focal length has on perspective is one that is often misunderstood and is bound to start a heated discussion on every online photography forum where it is mentioned.
Since I have personally participated in such a discussion more than once, I decided that I would write an article about the issue, demonstrating my conclusions as scientifically as I could: with photographs.
We often hear that a wide-angle lens provides a specific perspective, by making objects that are close to the lens more prominent and exaggerating the distances between image planes, while a telephoto tends to compress perspective and make the foreground appear closer to the background.
Strictly speaking, none of this is true but if you dare to say as much on an online forum, the discussion will soon degenerate and friendships will be broken. As a consequence, I’ve stopped arguing this point and, now that I have written this article, I will simply start pointing people to it, without comment.
What do I mean, exactly, by saying that the above is false?
To avoid any confusion, I will state my thesis in very clear and non-ambiguous terms:
Focal length does not directly influence perspective.
An alternative, but equivalent statement would be:
All other things being equal,
perspective is not influenced by changes in focal length.
At this point, you can either trust me or read below for the demonstration.
Still with me? Good. For the purpose of this demonstration, let’s first define what we mean by perspective, as I don’t think there can be any ambiguity about the definition of focal length. While the word perspective has different meanings depending on context, there is one that is of interest to photographers:
From the Merriam-Webster dictionary:
Perspective, noun: 4. The appearance to the eye of objects in respect to their relative distance and positions
Perspective, in the context of vision and visual perception, is the way in which objects appear to the eye based on their spatial attributes; or their dimensions and the position of the eye relative to the objects.
From these definitions, it should be clear that what we are interested in evaluating is the possible changes in the relative dimensions and the positions of the objects contained within the photographic frame as the focal length changes.
I could use geometry or trigonometry to demonstrate this, but people come to this site to read about photography, not mathematical proofs, so let’s demonstrate this using images.
The first image was taken at a focal length of 33.2mm lens on a crop-sensor camera (multiply that length by 1.5 if you want to relate it to a 35mm full-frame equivalent, but that is irrelevant for this discussion).
In taking the second image, I didn’t change my position or aperture, only the focal length, going from 33.2mm to 55mm.
In order to make the comparison easier, I cropped the first image so that the enlargement would be approximately the same:
As you can see in the screenshot below, showing the cropped version of the photo taken at 33.2mm side by side with the one taken at 55mm, the two images are almost perfectly identical, demonstrating that perspective didn’t change when zooming in.
You can show the two images to anyone and nobody will be able to say which one was taken with which focal length, unless they are able to discern the loss of resolution caused by cropping.
I think this should put to rest any claim that changes in focal length alone have an effect on perspective. So why do most people, including expert photographers, often mention the typical characteristics of wide-angle lenses, as opposed to telephotos with respect to perspective and expound on the different looks of wide angles and telephotos?
Well, to be honest, they are not wrong. To be continued… in Focal Length and Perspective: Part 2