What You Need To Know About Focal Length

In this article on What You Need To Know About Focal Length, we look at understanding the basics of focal length, a crucial relationship between a lens and the sensor or film of a camera. Mastering this setting is necessary to achieve the highest quality photographs possible and know which lenses to buy and use to achieve your creative visions. What You Need To Know About Focal Length, What You Need To Know About Focal Length

1. What Is Focal Length?

Measured in millimetres focal length is the distance between the point of convergence between the lens and a camera’s sensor or film. This rule is universal across all brands, formats and apertures and will never vary.

The focal length used will ultimately result in the field of view recorded in a composition. For example, a lens with a low focal length, such as 16mm, will have a wider field of view than a focal length of 150mm, which will be much narrower.

The term field of view relates to how much of a scene incorporates into a composition. A wide field of view will include more in a photograph, whereas a narrow field of view will zoom into a subject with more precision.

2. How Does Focal Length Affect An Image?

The distance between the lens and sensor or film impacts a composition in several ways. Understanding how these relationships work is paramount to achieving your creative vision. As well as making sure you select the right lens for your needs when making a purchasing decision.

2.1. Field Of View

As discussed above, the field of view relates to the amount of a scene exposed in a composition. Low focal lengths such as those with wide-angle lenses can grandly capture dramatic landscapes because they can fit more into an image.

On the other hand, telephoto lenses use high focal lengths, perfect for zooming into tight compositions. This zoom factor makes them ideal tools in wildlife photography, where it is essential to zoom into a subject like a bird or a fox without scaring them away.

2.2. Depth Of Field

Depth of field is the amount of an image in acceptable focus and varies significantly across different focal lengths. Low focal lengths have an elongated depth of field, which make them perfect for photographing large scenes. On the other hand, long focal lengths have a more compacted depth of field, making them more suited for honing in on a single subject or part of a subject.

A shallow depth of field also allows a lens to focus on smaller objects, even at a distance.

2.3. Perspective

The focal length of a lens can also change the perspective of an image. For example, a fisheye lens using a 180-degree field of view will warp the edges of a composition so much that it can give the illusion of a perfect sphere. In contrast, a long focal length compresses an image so much it gives a stacked appearance of elements in a photograph. This compression can make things in the background appear far closer to the foreground subject and is how photographers achieve things like large moons in their images.

2.4. Image Shake

Although not something that is directly related to the effect of focal length on imagery. It is important to note that as focal length increases, so does a camera’s sensitivity to vibration. So much so that even pushing the shutter button can result in a blurry image. It is vital to use accessories like remote shutters when using long focal lengths to stop this from happening.

3. The Difference Between Focal Length And Focal Distance

Focal length is the distance between the point of convergence between the lens and a camera’s sensor or film. It is a measurement that is inside a camera.

Conversely, focal distance is a measurement outside a camera and refers to the distance between a camera’s sensor or film and the subject itself. Lenses that work with shorter focal lengths have high levels of magnification. Lenses with short focal distances are called macro lenses and are used to photograph small subjects like insects.

4. How Sensor Size Affects Focal Length

Different digital system cameras use different sensor sizes. The most common are micro 4/3rds, APS-C, full-frame and medium format. A full-frame sized sensor takes its name because it shares the same sized sensor as analogue film.

Because digital cameras use different sized sensors, it changes the field of view when using the same focal length in a lens. The smaller the sensor is, the narrower the field of view becomes.

By taking the crop factor of a specific sensor and multiplying it by the field of view, we get the field of view as if it was a full-frame equivalent view.

For example, using a 35mm lens with an APS-C with a crop factor of 1.5x will result in the same field of view of a full-frame using a 50mm focal length.

5. How To Choose The Right Focal Length

There is no one size fits all focal length in photography. The list below will give you a better understanding of which focal lengths are suitable for different types of photography.

5.1. Ultra wide-angle 8mm – 24mm

Ultra wide-angle lenses have excessive fields of view. They increase the field of view so much that the outside of the composition become warped like a sphere. When the focal length drops below 10 millimetres, this effect becomes further exaggerated. Commonly referred to as fisheye lenses, a lens below 10mm will warp an image so much that a photograph can become a perfect circle.

Ultra-wide-angle focal lengths are suitable for creative shots and event photography. Furthermore, they are also popular with extreme sports photography such as skateboarding and BMX.

5.2. Standard wide-angle 24mm -35mm

Standard-wide angle lenses use encompassing fields of view with minimal distortion. However, moving closer to a subject by decreasing the focal distance is more likely to create subject warping. Depending on the focal length used the edges may also become warped. However this outer warping is usually fixable in post production.

Because standard wide angles can catch a lot of information in an image, it makes them ideal for photography such as photojournalism, where it is vital to capture the context of a subject to better tell its story. When using a wide-angle field of views, they can often make things appear more distant than they are.

5.3. Standard lens 35mm – 70mm

These standard focal lengths are typical among kit lenses that come paired with system cameras. Focal lengths within this range tend to render images closer to how the human eye sees the world. Because of this, the results tend to be more appealing to viewers.

A zoom lens using these focal lengths is capable of effectively capturing anything from landscape to portrait photography. This versatility makes them highly effective pieces of equipment and should be a staple in any photographers kit bag.

5.4. Telephoto lens 70mm – 300mm

Telephoto lenses can zoom in to compositions and have highly narrow fields of view. The increased focal length also amplifies the blurriness of a background. The zoom factor makes them perfect for things like wildlife and sports photography, where it’s impossible to be close to a subject. Likewise, the added bokeh or blurriness made with these lenses also makes them ideal for portrait photography.

6. Conclusion

The focal length used in a lens will impact the overall image considerably. Understanding the roles each will play in an outcome is vital to achieve the best shot for a scene and fulfil your creative vision.

As a beginner photographer, you may not have several lenses at your disposal. However, if you have a system camera, you most likely have at least a kit lens. If this is the case, perfect. You have the ideal lens to begin learning the basics of focal length and understand the relationship between focal length and the final image.

The best way to learn is to experiment. Try shooting the same subject or scene with varying focal lengths and apertures to see how these settings affect the image. Soon enough, you will exactly know what settings to dial in to achieve the desired result.

What You Need To Know About Focal Length, What You Need To Know About Focal Length, What You Need To Know About Focal Length

David Davis
David Davishttps://shuttergang.com
Hi, My name is Dave, and I am passionate about photography. I am currently travelling to document the world's most interesting people and places. I have started this blog to share these incredible sights and experiences with you, including all the knowledge I gain as a photographer/videographer along the way. If you share a passion for street, documentary, and travel photography, join the mailing list and stay up to date with the latest posts and resources direct from the field.

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