What is focal length of a lens? Why does focal length matter? And most importantly, how does focal length affect your image?
As an amateur photographer with five years of experience, I often get asked this from new photographers.
In fact, different focal lengths can completely change and give your picture a new look and quality.
In this article, I will explain this important technical term to you, and show you how different focal lengths work to improve your photography.
Please remember that this article was written for beginners. Therefore, many of the terms and explanations are simplified.
What is Lens Focal Length?
Technically speaking, focal length is the distance between the optical center of the lens and the camera sensor when the lens is focused on infinity.
A lens’ optical center is a single point of focus within a lens, at which the rays of light entering the lens are assumed to converge.
As the key values of a photographic lens, focal length is measured in millimeters (mm), like 50mm, 100mm, 24-70mm, etc.
You will find focal length information on the lens barrel or the lens body, and lenses are named by their focal length. Example: Sony FE 85mm f/1.4, and Sigma 14-24mm f/2.8.
A simple rule of focal length is:
The Smaller the Number = the Further You Are Getting to the Subject = Show More of the Scene
The Larger the Number = the Closer You Are Getting to the Subject = Show Less of the Scene
Why Focal Length Matters
Focal length of a lens is an essential factor to consider when deciding what lens to use to capture a given scene.
Focal length impacts your photographic composition – how much or little of a scene you capture – by magnifying subjects or making subjects decrease in apparent size.
For example, if you take a selfie with your phone’s camera wide-angle lens with a short focal length, your nose will appear disproportionately large and unattractive. Why?
Because the short focal length of your phone camera, usually 14 mm or 24 mm, distorts your face and enlarges your nose.
On the other hand, a “standard” 50mm lens with a normal focal length reproduces the proportions of faces, creating a more natural feel for your nose.
Focal Length and Field of View
Field of view means how much of a scene is “seen” by the image sensor through the lens.
Field of view is determined by the focal length of the lens and the camera’s sensor size. For most camera manufacturers, field of view (FOV) is the same as ‘angle of view’.
Focal Length Affects Composition
Varying focal lengths of a lens provide different image effects. It influences photographic composition in three aspects:
- Angle of view
- Object size
1. Angle of View
Focal length of a lens determines the angle of view—how much of the scene or how many degrees of view you capture in a picture.
longer the focal lengths = narrower angles of view
shorter the focal lengths = wider angles of view
Understanding focal length and how it affects your angle of view is crucial for making a good composition.
Changing the focal length alters the angle of view:
- Short focal lengths, like 24mm focal length, have wider/larger angles of view since more of the scene is captured.
- Middle focal lengths, like 50mm focal length, have similar angles of view to the human eye.
- Long focal lengths, like 200mm focal length, have narrower/smaller angles of view since less amount of the scene is captured.
shorter focal length = greater extent of the scene being captured
longer focal length = smaller extent of the scene being captured
Focal Lengths and Angles of View in Degrees
Different focal lengths have different angles of view in degrees.
- A 50 mm standard lens has an angle of view of 45 degrees.
- A fisheye lens has an angle of view of more than 180 degrees that takes everything in front of you.
- A 360-degree camera lens has an incredibly wide angle of view of 360 degrees that captures everything around you.
- The human eye’s focal length varies between 17mm and 25mm, with an angle view of over 180 degrees, given that we have two eyes.
However, the human eyes can actively perceive a small area, similar to a 40-50mm lens. This explains why the 50mm is called the ‘standard’ focal length.
Remember the angle of view is determined by not only the lens’s focal length but also the format of the camera’s sensor. 35 mm full-frame and APS-C format cameras will have different angles of view.
2. Object size
Object size is determined by the magnification of a lens—how large individual objects will be in a picture.
For example, telephoto lenses with large focal lengths make distant objects appear much larger/closer because of higher magnification. This allows you to take photos of distant objects without disturbing them.
Conversely, wide-angle lenses with short focal lengths do just the opposite, making the object appear smaller/further away because of lower magnification; you get close to your subject and still fit the foreground and background in your picture.
The lens compression effect refers to when shooting with a wide-angle lens with short focal length, subjects feel far apart from each other —foreground subjects become more prominent and closer.
In contrast, background subjects become smaller and further away, creating a sense of openness and space.
However, when shooting with a telephoto lens (large focal length), foreground, middle, and background subjects feel closer to each other. Simply put, the longer the focal length of a lens, the more compression causes.
This is because the telephoto lens “flattens” or “compresses” the scenes, creating a sense of diminished space and crowding.
How Crop Factor Impacts Focal Length
Camera’s sensor converts the light into electrical signals. The larger the sensor, the more light it captures and the more image information it can gather.
In addition, a large sensor has a better dynamic range, so it can display larger differences in brightness without loss of detail, and produces less image noise.
Full Frame vs. Crop Sensors
Digital cameras have a wide variety of sensor sizes like APS-C, full frame, micro four thirds, medium format and so on, depending on the manufacturer and camera model.
When digital sensors were invented, 35mm film(36 x 24mm image) was used as the standard and is called “full frame.”
Other camera sensor sizes, such as APS-C, micro four thirds, are usually smaller than full-frame. These sensors that are smaller than full frame are called cropped sensors.
For a given focal length, a crop sensor camera captures a smaller view in a smaller image, compared with a full-frame one.
Below are the most commonly used sensor sizes for both full frame sensor cameras and crop sensor cameras:
- Full frame / full format (36.00 x 24.00 mm)
- APS-H (27.90 x 18.60mm)
- APS-C (23.60 x 15.60mm))
- APS-C Canon (22.20 x 14.80mm)
- 1.5″ (18.70 x 14.00mm)
- Micro Four Thirds 4/3″ (17.30 x 13.00 mm)
- 1″ (12.80 x 9.60mm)
- 1/1.2″ (10.67 x 8.00mm)
- 2/3″ (8.80 x 6.60mm)
- 1/1.7″ (7.60 x 5.7mm)
- 1/2.3″ (6.17 x 4.55mm)
- 1/3.2″ (4.54 x 3.42mm)
Comparison of Sensor Sizes for Both Full Frame and Crop sensor Cameras:
The 35mm Film as A Reference Size
When comparing lens focal lengths, a traditional 35mm film frame (full frame camera) sensor always serves as a reference size for all camera sensor sizes. Each sensor size is therefore measured against this 35mm film frame (full frame camera)
What Is Crop Factor?
The crop factor is the ratio of a camera sensor’s size to a traditional 35mm film frame (full frame sensor cameras). Crop factor converts focal lengths between your camera’s sensor size and a traditional 35mm film frame (full-frame camera).
If you compare a smaller sensor to the full format, there is a factor X. Sensor A is therefore X times smaller than the full format. This factor is called the crop factor.
The calculation of converting focal lengths is very easy. Simply multiply the focal length of a lens with your cammer’s crop factor to convert focal lengths between the two sensor sizes.
Full Frame Sensor Cameras Don’t Have a Crop Factor
Only crop sensor cameras have a crop factor, while full frame sensor cameras don’t have a crop factor.
For this reason, crop sensor camera lenses have a smaller angle of view than their full frame counterparts.
For example, when shooting with a 35mm wide-angle lens, if your camera has a crop factor of 2x, your equivalent focal length becomes 70mm.
At Canon’s crop sensor cameras, the crop factor is 1.6. For Nikon’s DX crop sensor cameras, the crop factor is 1.5. At Sony’s crop sensor cameras, the crop factor is 2.7.
Cameras with higher crop factors produce a narrower field of view that leaves the impression of a longer focal length.
You have to pay attention to the specified focal length of your lens whether you mount that lens on the full format camera or on the APS-C format camera.
Classifications of Focal Lengths
Depending on the equivalent focal length, the lenses are classified into five classes:
- Ultra wide-angle lens: focal length 8mm to 24mm
- Wide-angle lens: focal length 24mm to 35mm
- Normal lens: focal length 35mm to 70mm
- Telephoto lens: focal length 70mm to 300mm
- Super telephoto lens: focal length 300mm to 600mm and above
Lens Focal Length Comparison
1. Wide-angle Lens (24mm lens to 35mm lens)
A wide-angle lens has a wider field of view than the human eye which allows you to capture much more of the scene than a normal lens, and your pictures look more dynamic and three-dimensional.
These focal length lenses provide greater depth of field than a normal or telephoto one. For this reason, these focal length lenses are ideal for capturing the scenes as much as possible when photographing
- and large group photos
However, taking portraits with a wide-angle lens can be tricky because it showcases much of the surrounding environment.
Alternatively, the best focal length for portraits is 85mm or larger which works perfectly for full-length and close-up portraits.
2. Ultra-wide Angle Lens (8mm lens to 24mm lens)
Ultra-wide angle Lenses with short focal lengths are very extreme wide-angle lenses that allow you to catch things behind you and shoot almost “all-around”!
Ultra-wide angle Lenses have a close minimum focusing distance and a large depth of field. They capture wide views, and bring strong distortions due to the large angles of view.
An example of such an extremely wide-angle lens is the GoPro action camera which is used for
- and everyday life
You can attach a GoPro action camera to your
- ski helmet
- or anywhere else
3. Normal Lens (35mm lens to 70mm lens)
Normal lenses, also called standard lenses, are a popular choice as they have similar angles of view to the human eye.
The big advantage of normal lenses is they cause minimal distortion.
You have fairly much of the scene with you, but you can also shoot headshots with little distortion. This is great for portraits and landscape photography.
4. Telephoto Lens (70mm lens to 300mm lens)
Telephoto lenses are ideal for picking a distant subject when photographing
- and wildlife
Undoubtedly, the 85mm lens is the best portrait lens in the market.
It offers a narrow-angle of view than the 35mm and 50mm lenses, so you don’t get much of the environment in your composition.
This is quite helpful if you want to create portrait photos without too much background with the main subject.
With a large aperture and shallow depth of field, you can easily separate your subject from the background.
Plus, an 85mm lens is great for shooting both close-up headshots and full-body shots as it causes little facial distortions to your subject.
However, pictures taken with an 85mm lens may look ‘flat’ (a very two-dimensional look) and less vivid than with a wide-angle lens.
5. Super Telephoto Lens (300mm lens to 600mm lens and Above)
Super telephoto lenses with a large focal length of 300mm and above are popular in nature and sports photography.
Although the depth of field is razor-thin, super telephoto lenses are a must for wildlife/sports photographers because they combine the effect of binoculars with a camera.
Another good thing about these focal-length lenses is they have a condensing effect. They bring together in the picture what is far apart in reality like
- mountain ridges
- animals in a herd
- and racing cars racing toward the photographer on the straight
With a long focal length, animals, athletes, and photographers stay at a safe distance.
However, with increasing focal length, telephoto lenses become larger, and with increasing light intensity, they become heavier and more expensive.
Long Focal Lengths and Background Compression
Long focal lengths bring the background closer to the subject or background compression to your image, creating a tunnel vision effect.
However, background compression can be good or bad – depending on what effect you want to create.
For example, if you want a little of the environment in your portrait pictures, a long focal length lens will enhance the overall composition.
On the other hand, if you’re going to incorporate a lot of the surroundings in your photo, a wide-angle lens works best for you.
Summary of the Image Effects by Various Focal Lengths
- Wide-angle lens = dynamism
- Normal lens = balance, and harmony
- Telephoto lens = flat
Zoom vs. Prime
Lenses are divided into prime lenses and zoom lenses based on focal length.
Prime lenses, also called fixed focal length lenses, have just one fixed focal length. For example, a 35mm prime lens has just a focal length of 35mm.
There are interchangeable prime lenses across all focal length ranges, including:
- macro lenses
- fisheye lenses
- super-telephoto lenses
- tilt-shift lenses (for perspective correction, maximizing/minimizing depth-of-field, and panoramic photography)
Here are some focal length examples of prime lenses for beginners to consider: A 28mm lens, a 35mm lens, an 50mm lens, and an 85mm lens, etc. Among them, the most popular primes are 35mm, 50mm, 85mm, 135mm, and 200mm.
On the other hand, zoom lenses cover a range of focal lengths in a single lens.
If you just bought a new DSLR, the kit lens with your camera is a zoom lens, most likely an 18-55mm zoom lens.
This means the lens covers a range of focal lengths between 18mm and 55mm, making taking photos conveniently.
Also, there are interchangeable zoom lenses across all focal length ranges, including:
- wide-angle zoom lenses (24-35 mm)
- standard zoom lenses (35-80 mm)
- telephoto zoom lenses (80-300 mm)
Here are some focal length examples of zoom lenses for beginners to consider: 18-55mm kit lens, 24-70mm lens, and 28-300mm lens. The popular zoom lenses are 18-55mm, 18-135mm, and 18-200mm.
Prime vs. Zoom | Pros & Cons
In general, prime lenses are
and often have a wider, faster aperture than their zoom counterparts.
Using prime lenses with large apertures so you get a shallow depth of field. This is useful for shooting portraits where you want a softer or blurred background.
Moreover, prime lenses perform better in low-light environments than zoom ones.
On the other hand, zoom lenses allow you to use a single lens that covers almost a full range of focal lengths rather than carrying 14mm, 50mm, and 85mm prime lenses.
Furthermore, you’ll never worry about changing camera lenses and risk getting dust or water in your image sensor.
How Focal Length Affects Perspective
Lenses of different focal lengths change the perspective of your images.
Wide-angle lenses exaggerate the scene’s space, and create more room, and depth between the elements in your images.
Conversely, telephoto lenses flatten the space and compress the scene’s depth.
How to Select a Camera Lens for Focal Length?
In general, certain lenses will perform better due to the focal lengths, whether you focus on
- or architecture
Prime lenses are absolutely the best choice for beginners photographers.
With prime lenses, you have to move around and think about composition much more – rather than staying in the same physical position and just zooming in or out to compose.
Moreover, prime lenses will force you
- to think about your setting.
- to think about how to use your camera.
- to be more creative with one focal length
Because of that, you will quickly learn more about the relationship between perspective and camera-to-subject distance. That alone will improve your photography a lot.
Prime lenses like 50mm and 85mm lenses usually work best for professional portrait photographers.
That is because prime lenses isolate the subject from the background and create a beautifully blurred background.
Wide-angle lenses with exaggerated perspectives are most often recommended for journalists and landscape photographers, which allows photographers to include lots of context in the image.
For example, 35mm is a classic focal length for journalists working for
- online media
- and academia
Meanwhile, many street photographers lean toward using 50 mm lenses since they offer a similar view to the human eye or the human field of view. This is called the “human perspective.” Humans have an approximate field of view of approx. 180° – 200°.
A telephoto lens is the best-suited option for sports or wildlife photographers.
A medium telephoto is useful for shooting in and around zoos and wildlife parks.
If you’re capturing smaller subjects, such as birds on the backyard feeder, a telephoto with much more reach (300mm +) works best for you.
If you don’t know what lens works for you, you won’t go wrong with a good “do it all” zoom lens.
Now that you know what focal length is and how to choose the proper focal length when composing a shot. So go out and shoot as much as possible; the more you do it, the better you can get.
With enough practice, I promise your photography skills will improve a lot. The best focal length you have is the one in your hand.