The question of what effect focal length in photography 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 wide angle lenses 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 lenses 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:
Changes in focal length of a camera lens 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 of a camera lens.
At this point, you can either trust me or read below for the demonstration.
Still with me? Good.
What is Perspective in Photography?
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 of a camera lens 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.
Perspective & Focal Length of Camera Lenses
Here are some landscape photos from Finnich Glen, in Scotland, a deep gully cut through the earth by a small river, with steep walls covered in moss. The rock at the end is called the Devil’s Pulpit. It’s a fascinating location that lets me illustrate the concepts presented in this article, given how easy it is to include near and far objects in the same frame.
Image #1 below was taken at a focal length of 33mm wide angle 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, as mentioned above).
Image #2, I didn’t change my position or aperture, only the focal length, going from 33mm to 55mm. In order to make the comparison easier, I cropped the Image #1 so that the enlargement would be approximately the same as 55mm focal lenght (Image #3).
As you can see in the landscape photos above, showing the cropped version of the photo taken at 33mm focal lenght side by side with the one taken at 55mm camera lens, 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 of camera lenses alone have an effect on perspective in photography. So why do most people, including expert nature photographers, often mention the typical characteristics of wide-angle lenses, as opposed to telephotos lenses with respect to perspective and expound on the different looks of wide angles and telephotos lenses?
Well, to be honest, they do consider keep “everything else” the same. So lets take a look at what happens when we start changing the position of the camera lenses with respect to your subjects.
Subject Distance & Perspective in Photography
Let’s look at my thesis again, with some emphasis added:
Changes in focal length of a camera lens does not directly influence perspective.
The key word here is directly. If you remove this word, my thesis is no longer precise because there are ways that focal length of a camera lens indirectly influences perspective in photography. But what does directly influence perspective? That’s easy…
Perspective is influenced exclusively by the relative positions of the subjects in the scene with respect to the position of the camera.
In other words, you can only change perspective by changing position your camera lens, not by changing the focal length. To demonstrate this, after I took the previous images, I chose this particular subject because it has basically just two image planes: the façade of the castle and the guard tower. The two were once connected by a drawbridge that has now been replaced by a stone bridge. I took another series of images at a location near my home, this time using a camera lens with focal length of 24mm and moving the camera forward.
Here are those images…
As I approach the castle, you can clearly see how the relationship between the apparent sizes of the subjects (that is the perspective) changes, with the nearest arch becoming bigger faster than the background and revealing more of the slits that used to hold the lifting arms of the drawbridge and of the window between them.
You can also see that the last image (Image #4) in the series is starting to acquire some of the characteristics we typically attribute to the use of wide angle lenses: prominence of foreground and vertical lines that converge when tilting up the camera.
If somebody only looked at the first image, they would not be able to tell whether it was taken with a wide angle lens or with a telephoto lens, not knowing the distance from which it was taken. However, you would not be able to take the last image (Image #4) with a telephoto lens; you would be too close to include those objects in the frame.
So, what do people mean when they say that camera lens focal length has an effect on perspective in photography? To put it simply, if they know what they are talking about, they mean that a given focal length of your camera lens allows you to move closer or farther away from your subject and that is what determines perspective in photography.
In other words, focal length influences perspective indirectly by way of changing your camera lens position.
As a final illustration of the concept, I want to share these two photos, taken at the same focal length, but where I moved my position between photos.
The image (Image #1) from farther away was then resized so that the central subject would be the same size as in the image capture from close up (Image #2). This demonstrates very graphically how perspective changes by changing position of your camera lens but keeping the same focal length.
Crop Factor Camera & Focal Length
So just how does crop factor effect the perspective in photography? We know that mounting a 50mm lens on an APS-C camera effectively makes it a 75mm camera lens. However remember that the focal length is a characteristic of the camera lens and does not change if you crop the photo or mount it on a crop factor camera. What changes is the field of view, so we can say that a 50mm camera lens, when mounted on a crop-sensor (APS-C) camera, gives roughly the same field of view as a 75mm camera lens mounted on a full-frame sensor. And as we have seen from this article that copping an image does not change the perspective.
Keep in mind that all the photos presented in this article were taken with apertures that guarantee sufficient depth-of-field, from the foreground to the most distant objects. Please keep in mind that focal length affects depth-of-field, so even though perspective is unchanged, zooming in and out might affect your landscape photos by making parts of them look more or less out of focus with respect to others.
I know geometric optics are not easy to understand, so I tried to stay away from maths and use practical photos for this article. At the end of it, the one thing you should keep in mind, when deciding what to do in order to balance your photography compositions with a judicious placement of objects that sit at different distances from your camera lens: Zooming with your feet is the only way to change perspective. Don’t get lazy and think that you can do everything by zooming in with your camera lens.