Why Focal Length Is Also a Question of the Right Perspective

The right focal length is also a question of perspective
What can wide-angle lenses and zoom lenses do for storytelling? | © Pixabay

The choice of the right camera lens is a cinematic design tool of the first order. It has a decisive influence on the effect of the picture. FILMPULS explains what wide-angle lenses, zoom lenses and focal length can do for storytelling in film and video.

Just like camera movements, tracking shots and panning shots, working with lenses is an important part of creating images for moving pictures.

You need to know

  • Focal lengths are determined by the choice of lens (the camera lens).
  • Long focal lengths (telephoto) reduce the depth of space and have a limited depth of field.
  • Short focal lengths (wide angle) have the opposite effect of a telephoto lens. Foreground and background differ greatly in the effect of the picture.
  • A distinction is made between a normal lens, a telephoto lens and a wide-angle lens. Normal means the closest possible approximation to the natural visual experience.

The focal length determines the image

An example to illustrate:

If an actor is standing in front of a house and needs to appear the same size in shots with a telephoto or wide-angle lens (because that’s dictated by the story), the camera needs to be much closer to the actor for the wide-angle shot than in the telephoto shot. This change in camera location results in a change in the relationship between foreground and background.

In the telephoto shot, the background is much more present than in the wide-angle shot, which makes the background appear much smaller. So depending on the plot and what he wants to say, the cinematographer will choose one option or the other.

The focal length helps shape the storytelling

Shooting with a telephoto lens (long focal lengths) reduces the impression of space. They take away the plasticity of a shot and make it appear interlaced in perspective. Telephoto shots are perceived by the viewer as flat, striking and lacking in perspective reference. Movements seem delayed (treading water) compared to normal recordings.

At the same time, the depth of field is limited when shooting with a telephoto lens: Due to the blurriness, it leaves the viewer in the dark as to what exactly it looks like in front of and behind the plane of action, thus opening up a lot of room for induction.

Conversely, film images shot with a short focal length (wide angle) emphasize spatial perspective. In a wide-angle shot, an object is more clearly separated from the background than when the identical subject is shot with a telephoto lens.

Wide-angle shots are good for drawing the viewer into the image. The viewer becomes part of the film image and stands in the middle of the action. This effect is again significantly enhanced by showing a film on a big screen, unlike when the same sequence of images is viewed on a smartphone.

With extreme wide-angle shots, the perspective can quickly appear overdrawn. As a rule, however, wide-angle shots enhance the feeling of standing in a real room as a viewer. Why? Because we can grasp the space as a whole and not just see a part of it.

Unlike a telephoto lens, movements in front of a wide-angle lens can quickly seem hectic, rushed or too fast. This optical dynamic is of utmost importance for the image design and the artistic work of the director and cinematographer. As always, it can also be deliberately chosen and used for storytelling.

Focal length, aperture and focus

Wide-angle shots have a greater depth of field (at the same shooting distance and with the same aperture) than shots taken with a telephoto lens. Conversely, the depth of field remains almost comparable when a telephoto shot and a wide-angle shot are taken with the camera shifted to keep the size of the subject the same. Focal length and aperture have in common that they have a great influence on image sharpness.

For the aperture, the wider the aperture is open, the less depth of field the image will have. The blur is getting bigger. The wider the aperture is closed, the more depth of field and the less blur there is. Depending on the lighting conditions, the camera operator can also compose the film image to suit the story.

Image sharpness, not sharpness level, is also purely a practical issue for choosing between these two types of camera lenses. A wide-angle shot taken without a tripod looks far less blurred than a telephoto lens, even if the camera is shaky.

A question of perspective

The focal length of a lens, together with the shooting format, determines the angle of view. Or to put it another way: The perspective effect is a consequence of the image ratio of foreground to background. If the aspect ratio of a video is 16 : 9 (width to height), this results in a larger horizontal angle of view than in the vertical. Likewise, the viewing angle also has an influence on the image illumination.

The question of the correct perspective is therefore not only determined by the viewing height (bird’s eye view, frog’s eye view) or the viewing angle on an object (frontal, sideways, etc.), but always also by the choice of lens.

Normal lens, wide-angle lens and telephoto lens

What is called a normal focal length is nothing more than an attempt to use a camera lens to depict an event as close as possible to the human visual experience. That this definition of “normal” is honourable but also problematic is shown by the fact alone that the filmmaker cannot control the distance of the viewer to the image himself.

Those sitting in the front row of the cinema see the image on the big screen differently than those in the back rows watching the film. For decades, the recommended ideal distance to a TV set was the formula: Multiply the screen diagonal by a factor of 3 (for flat screens, the recommended distance is now screen diagonal in inches x 4.2). Nevertheless, very few buyers of a TV set calculate on the basis of their living room how big the new TV should be.

Physically, the viewing experience for the cinema audience in the front row is as natural as possible when they see a wide-angle image. Conversely, again from an optics and physics point of view, anyone watching TV on a smartphone will perceive footage created only through a telephoto lens as normal.

For once, the truth lies somewhere in the middle. Perspective tapering of an image is physically normal when the viewer is looking at it from the distance of the shooting focal length, multiplied by the scale of magnification where necessary.

Focal lengths of different lenses

More important to the cameraman than the largely uncontrollable distance of the audience to the screen or flat screen must be those things that he can control. Lenses. There are more or less binding definitions for them:

  • Normal lenses are camera lenses that are as close as possible to human vision. One can orient oneself thereby at the point of view of the human eye. This detects an angle of 24° – 35°. Which value this is in concrete terms can only be determined correctly if the film format is known. As a rule of thumb, the focal length of a standard lens roughly corresponds to the diagonal of the film format in millimeters.
  • Lenses whose angle of view exceeds that of the eye, specifically lenses that have an angle wider than 35°, can be considered wide-angle lenses. They show close motifs larger in relation to the main motif (background) than in reality (so-called central perspective) and achieve an impressive depth effect.
  • Conversely, the angle of view of a telephoto lens is narrower than the minimum human angle of view of 24°. It always shows only a more limited section of a motif.

Compared to a normal lens or a wide-angle lens, a telephoto lens always shows only a section of the subject. False is the statement that the telephoto lens magnifies a subject. This impression is created only by the omission (the reduction to a section) of the environment.

The wide-angle lens, again using a normal shot as the starting point of observation, does just the opposite. It opens the viewer’s gaze and presents the space as the environment of the action.

Zoom lenses

In the sixties, driven by TV reports, it became common to use so-called transfocators (today called zoom lenses). A zoom lens has an infinitely variable focal length within a certain range.

This is made possible by a highly complex optical system that allows the front and rear main points to be shifted without affecting the plane of focus or the amount of light. Since the necessary calculations are carried out by the lens manufacturers with the aid of computers, the quality of zoom lenses has improved by leaps and bounds.

In the early years of their introduction, zoom lenses were jokingly referred to as rubber lenses. It wasn’t meant to be flattering.

There are 3 reasons why zoom lenses have become the most used lenses:

  1. A good zoom lens can largely replace the conventional lens set.
  2. The cameraman can adjust the focal length and thus the image section more quickly than is possible with a lens change
  3. Zooming allows the simulation of a camera movement, from close-up to long shot.

Camera movements imitated with a zoom are considered misuse by strict cineastes because the camera point of view does not change in the process, which can appear unnatural to the viewer.

Attachment lenses and converters

The focal length in the close-up range or in the wide-angle range can be further broken up (extended) with so-called attachment lenses. The multiplication factor of a close-up lens indicates whether the image with the close-up lens appears wide-angle (multiplication factor below 1) or less wide-angle (multiplication factor above 1).

Converters, which can be attached between the lens and the camera, extend the focal length. A converter with factor 2 doubles this value.

Unfortunately, this also automatically doubles lens aberrations that were barely noticeable and still tolerable without a converter, and suddenly they become a disturbing factor, and with a converter the light intensity decreases. This is why converters are only used in professional film in exceptional cases today.

In summary

Normal lenses

  • have a viewing angle that corresponds to that of humans (average value: 24°-35°),
  • appear rather inconspicuous, since the perspective of the normal lens corresponds to the natural visual impression of the eye.

Wide-angle lenses

  • have a viewing angle that is wider than that of humans (over 24°),
  • have more depth of field,
  • give more spatiality,
  • are suitable when shooting from the hand.

Telephoto lenses

  • the angle of vision is smaller than that of a human being (narrower than 35°),
  • have selective depth of field,
  • have a more graphic effect,
  • usually require a tripod,
  • connect distant objects,
  • the distance between the objects appears smaller than it is in reality,
  • the shot looks crowded, compressed and rather flat (parallel perspective)
  • there is hardly any spatial impression.

Whether wide-angle, telephoto or normal lens. It’s not the lens itself that makes a video exceptional, but the wise choice and considered use of the right focal length and camera perspective.

Further literature on focal length

  • Werner van Appeldorn: Handbook of Film and Television Production. Psychology Design Technique. Munich: 2nd revised edition, 1988

This article was automatically translated into English using AI. If you would like to help us improve the quality, we would be happy to hear from you.

Redaktion Filmpuls
About Redaktion Filmpuls 265 Articles
Unter der Bezeichnung »Redaktion Filmpuls« erscheinen Beiträge, die von mehreren Redaktionsmitgliedern gemeinsam erstellt oder bearbeitet wurden.

Be the first to comment

Leave a Reply

Your email address will not be published.


*