…Continued from Focal Length and Perspective: Part 1
In my last post I claimed that….
Let’s look at my thesis again, with some emphasis added:
Focal length 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 indirectly influences perspective. 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 your position, not by zooming in and out.
To demonstrate this, after I took the previous images from Part 1, I took another series of images, this time keeping the focal length at 24mm and moving the camera forward. Here are those 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 The two were once connected by a drawbridge that has now been replaced by a stone bridge.
As I approach the building, 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 drawbridge’s lifting arms and of the window between them.
You can also see that the last image 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 or with a telephoto, not knowing the distance from which it was taken. However, you would not be able to take the last image with a telephoto; you would be too close to include those objects in the frame (though you could fake it with miniatures).
So, what do people mean when they say that focal length has an effect on perspective? To put it simply, if they know what they are talking about, they mean that a given focal length allows you to move closer or farther away from your subject and that is what determines perspective.
In other words, focal length influences perspective indirectly by way of changes in camera position.
As a final illustration of the concept, I want to share this animation, comprising two photos taken at the same focal length, but where I moved my position between shots. The image from farther away was then resized so that the central subject would be the same size as in the other image. This demonstrates very graphically how perspective changes by changing position but keeping the same focal length.
Click on the image to see the animation.