What Is the Focal Length of a Lens?
The focal length of a lens is a key term that defines the basic characteristic of any photographic lens. It is the distance between the optical centre of the lens and the point at which light rays are focused to form a sharp image on the camera sensor or film. The focal length, expressed in millimetres, determines how much of the scene will be captured by the lens and how the perspective of the photograph will appear.
The graphic above illustrates how changing the focal length of the lens affects what and how it is seen in the camera frame. Each colour in the diagram represents a different range of focal lengths, from ultra wide-angle (fisheye) to super telephoto, and shows how the angle of view changes when using them.
Fisheye and Wide Angles
At the bottom of the graphic we start with fisheye lenses, which offer extremely wide angles of view of up to 180°. Fisheye lenses are mainly used for specialised applications, such as striking shots of panoramas, architecture or interiors, where you want to capture as much space as possible in one frame.
Going higher, we see lenses with a focal length of 14 mm, which are also classified as ultra wide-angle, but already without such drastic distortion as the fisheye. These lenses offer an angle of view of around 114°, which is ideal for shooting wide landscapes or large groups of people.
Standard and Medium Telephoto Lenses
Moving on to 35mm and 50mm focal lengths, we enter what is considered the ‘normal’ category. These focal lengths give an angle of view close to how the human eye perceives the world, with no additional magnification or distortion. They are ideal for everyday shots, street photography or simple portraits.
Find out more:
Focal lengths from 85mm to 135mm are considered ideal for portraits. They allow for natural proportions of the face, blurring the background beautifully(bokeh effect), which focuses attention on the portrait subject. Telephoto lenses, such as 200mm, sharpen this effect, isolating the subject from the background even more effectively, which is appreciated in portrait, sports or nature photography.
Super Telephoto Lenses
At the top of the graphic are super telephoto lenses with focal lengths of 300mm, 400mm and beyond, which offer a very narrow angle of view, for example 8° for 400mm. These are used for photographing very distant subjects, such as wild animals or athletes in large arenas. They allow close-up and detailed shots of subjects that are inaccessible to standard lenses.
Effect of Focal Length on Image Composition
The focal length of a lens is crucial to photographic composition, affecting depth of field, perspective and the proportions of objects in a photograph. Understanding these relationships allows photographers to more consciously shape the visual message of their work.
The Importance of Focal Length for Depth of Field
Depthof field, or the range of sharp representation of space in a photograph, is closely related to the focal length used. Shorter focal lengths, such as 24mm, usually offer a wide depth of field, making almost the entire image from foreground to background sharp. This is ideal for landscapes where you want to capture both near and far elements. On the other hand, long focal lengths, such as 85mm used in portraits, allow the model to be isolated from the background by having a shallow depth of field, which focuses attention on the person and creates a soft, blurred background.
The choice of focal length should take into account both the technical aspects of the photograph and the emotional message you want to convey.
Focal Length Versus Perspective and Proportions in a Photograph
Focal length also has a direct impact on the perception of perspective in a photograph. Wide angles can distort perspective by magnifying objects close to the lens, which adds drama to the composition, but can also lead to an unnatural appearance of figures or objects. Longer focal lengths, such as 200mm, flatten the perspective, which can be used for a ‘compression’ effect, bringing distant subjects visually closer, which is often used in sports and nature photography.
How to Choose the Right Focal Length for Portrait, Landscape, Macro Photography
Choosing the right focal length is key to achieving the desired effect in different types of photography:
- Portraits – Focal lengths from 85mm to 135mm are ideal as they minimise facial distortion, ensuring natural proportions and allowing beautiful background blur.
- Landscapes – Wide angles such as 16-35mm allow you to capture wide scenes without significant distortion, ideal for panoramic views.
- Macro photography – Macro focal lengths, such as 100mm, offer sufficient working distance and great detail for close shots.
Types of Focal Lengths in Photography
There are many types of lens focal lengths that affect how you photograph different scenes. The basic division includes fixed and zoom focal lengths, also known as zooms. Each has its own specific uses and characteristics that make them more or less suitable for specific photographic tasks.
Fixed Focal Length
Fixed focal length lenses offer a single, unchanging focal length. They are prized for their brightness and sharpness, making them an ideal choice for photography where image quality is a priority. An example of this is the 50mm f/1.8 lens, popularly known as the ‘fifty’, which is known for its excellent colour and depth perception. This type of lens is often chosen by portrait photographers and photographers working in low light conditions.
Varifocal (zoom)
Varifocal lenses offer greater flexibility, allowing you to change the focal length without having to change lenses. They are ideal for photographers who need speed and versatility, for example in reportage or sports events. An example is the 24-70mm f/2.8 lens, which allows a wide range of frames from wide-angle to medium telephoto, which is useful in dynamic, unpredictable shooting scenarios.
Examples of Use
Landscape photography is dominated by wide angles, such as 16-35mm, which allow extensive scenes to be captured without significant perspective distortion. Conversely, telephoto lenses, such as 70-200mm or longer, are popular in sports or wildlife photography, allowing you to get close to faraway subjects without disturbing their natural behaviour.
The choice of focal length should be dictated by the specifics of the scene you want to capture.
Focal Length and Image Quality
The focal length of a lens affects not only the composition and perspective of a photograph, but also its quality. Aspects such as aberrations, sharpness or lens brightness are closely linked to the focal length chosen, which has a significant impact on the final image.
Aberration and Other Optical Distortions
Optical aberration is a design flaw in lenses that causes light passing through different parts of the lens to not be focused evenly, leading to image distortion. Lenses with shorter focal lengths, such as wide-angle lenses, are more likely to suffer from chromatic aberration, which manifests itself as a coloured halo around contrasting edges.
Long focal lengths, on the other hand, can generate spherical aberration, leading to focus problems at the edges of the frame. Lens manufacturers often implement various technologies, such as special coatings or low dispersion glass elements, to minimise these effects.
Effect of Focal Length on Lens Brightness and Sharpness
Focal length also affects the brightness of a lens, which is determined by the maximum aperture. Brighter lenses (with lower f values) allow you to shoot in lower light without having to increase the ISO or increase the shutter speed. Fixed focal length lenses often offer larger maximum apertures (e.g. f/1.4, f/1.8), making them ideal for low light conditions.
The sharpness of a lens is also related to the focal length. Longer focal lengths can offer better resolution of detail with distant subjects, but often require a steadier grip on the camera or the use of a tripod. Shorter focal lengths, on the other hand, are easier to use handheld and are more forgiving of minor camera shake.
Comparison of the Quality of Fixed and Zoom Lenses
Fixed focal length lenses are generally more highly regarded for their optical quality compared to zoom lenses. Fixed focal length lens design is usually simpler, allowing for better aberration control and higher image sharpness. Varifocal lenses, despite their versatility and convenience, often introduce compromises in terms of brightness and sharpness uniformity, especially at extreme focal lengths.
Focal length has a decisive impact on image quality, from aberration to brightness and sharpness, which is crucial when choosing the right lens.
Focal Length vs VR
Modern photography is constantly evolving and focal length plays a key role in this process. Advances in lens technology, including the introduction of vibration reduction (VR) systems and new approaches in cinematography, demonstrate the importance of focal length in shaping images and visual narrative.
Lenses With VR (vibration Reduction) and Their Impact on Image Stabilisation
Lenses equipped with VR (Vibration Reduction) significantly improve the quality of images in difficult conditions. This system compensates for camera shake, which is particularly important at longer focal lengths. For example, lenses such as the Nikon 70-200mm f/2.8 VR II allow photographers to capture sharp images at slower shutter speeds, which would be impossible without this technology. Statistics show that the VR system can improve the sharpness of photos at exposures up to 4 aperture stops longer than without stabilisation.
Modern lens technologies such as VR are revolutionising the possibilities of photography, allowing sharp images in conditions that would formerly have required a tripod.
The Use of Focal Lengths in Cinematography and the Impact on Visual Narrative
In cinematography, the focal length of a lens is crucial to the visual style of a film. Directors and camera operators use different focal lengths to tell a story in a more engaging way. For example, using wide focal lengths in action scenes can increase the dynamism and intensity of the experience.
Longer focal lengths are used for intimate, emotionally focused shots that isolate characters from their surroundings, focusing the viewer’s attention on the actors’ facial expressions and emotions.
Understanding focal length is vital for photographers and cinematographers alike, as it shapes the visual narrative and emotional impact of an image. Choosing the right focal length, whether for a dramatic wide-angle landscape or an intimate portrait with a pleasing bokeh effect, can make all the difference in visual storytelling. For example, the impact of focal length on composition and subject isolation is often harnessed in wildlife photography, allowing photographers to capture detailed shots of animals from a safe distance. Furthermore, the technological advancements in lenses, including image stabilization features, allow for greater creative freedom in hand-held shooting, helping artists to push the boundaries of their craft without being constrained by camera shake or suboptimal lighting conditions.
