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Focal Length: Everything You Need to Know

Learn about focal length in photography and why it is arguably the most important factor in camera lens specifications

For most photographers, focal length is the first thing to consider when choosing a lens as it has a direct relationship with the angle of view, which affects how much of your scene is visible in the frame, and indeed the magnification of your subject.

As such, a lens’s focal length is the first number you will read in the names of most lenses on the market. But what exactly is focal length, how is it calculated, and which focal lengths are best suited to which applications? In this article, we aim to answer all these questions with a complete guide to focal length.

What Is Focal Length?

As rays of light pass through the lens, there is a point at which they converge. Focal length is the distance in millimeters between this point of convergence and the sensor or photographic film of the camera it is attached to.

As you can see from Figure 1, a shorter focal length creates a wider angle of view, which means the subject appears smaller in the resulting image. Conversely, a longer focal length creates a narrower angle of view, which means the subject appears larger in the image.

Diagram explaining focal length

Figure 1: Long focal length vs. short focal length. For illustrative purposes only.

The Effect of Sensor Size

Now you understand the basic principles of focal length and angle of view – and how one affects the other – it’s time to make things a little more complicated.

Different digital cameras can have different-sized image sensors. For example, FUJIFILM X Series cameras use an APS-C sensor that measures 23.5×15.6mm, while FUJIFILM GFX System cameras use a much larger sensor measuring 43.9×32.9mm.

This means, for example, that although FUJINON XF50mmF2 R WR (X Series) and FUJINON GF50mmF3.5 R LM WR (GFX System) lenses both share a 50mm focal length, they actually produce very different images.

As you can see from Figure 2, while the focal length and angle of view remain the same in both cases, the field of view changes considerably with the size of the sensor.

Understandably, this has the potential to become quite confusing, that’s why the photographic industry works in 35mm equivalent focal lengths.

DIagram comparing sensor sizes and crop factor

Figure 2: GFX System vs. 35mm Format vs. X-Trans CMOS (APS-C) | Photo 2020 © Justin Black

What Is 35mm Equivalent Focal Length?

The 35mm equivalent focal length – often referred to as equivalent focal length, 35mm equivalent, or equivalence – is a way of standardizing focal lengths across all sensor sizes.

Before digital camera sensors were introduced, a camera would work by positioning a piece of photographic film over a shuttered opening, then releasing the spring-mounted shutter to let light through and make an exposure (learn more about the exposure process in our article about mirrorless cameras here).

The extremely popular 35mm analog film cameras all used the same-size opening, which measured 36x24mm. Using this size as a benchmark, the 35mm equivalent focal length is calculated depending on how many times bigger or smaller the sensor in question is. This difference in size is often referred to as ‘crop factor’.

The X-Trans CMOS sensor has a crop factor of 1.5. GFX System’s sensor has a crop factor of 0.79 (see Table 1). By multiplying the focal length of the lens by the crop factor of the sensor it’s compatible with, you can work out the lens’s 35mm equivalent.

Therefore, going back to our earlier example, XF50mmF2 R WR has an equivalent focal length of approximately 75mm, while GF50mmF3.5 R LM WR has an equivalent focal length of approximately 40mm.

Put another way: to achieve a 50mm equivalent focal length with an X Series camera, you need to attach XF33mmF1.4 R LM WR, whereas to do so with a GFX System camera you need to attach GF63mmF2.8 R WR.

 

Crop Factor Comparison Table

Sensor Type Dimensions Crop Factor
X Trans CMOS (APS-C) 23.5mm x 15.6mm 1.5
35mm Format 36mm x 24mm 1
GFX System 43.9mm x 32.9mm 0.79

Table 1: Comparison table for X-Trans CMOS APS-C, GFX, and 35mm Format

 

Guide to Focal Lengths

Focal lengths can vary dramatically. This has a huge impact on how a scene is framed and a subject is depicted. Different focal lengths are better suited to different genres and situations.

To make this easier to navigate, focal lengths are generally split into categories depending on their angle of view, from 8mm ultra wide-angle lenses to super telephoto lenses of more than 1800mm.

Read on to understand which focal length is best suited to your style of photography.

Focal length and angle of view guide

What Is an Ultra Wide-Angle Lens?

Focal length (35mm equivalent): Less than 24mm
Angle of view: More than 84°
Great for: Action, interior, astro
Not so great for: Portrait, wildlife, documentary

Ultra wide-angle lenses are lenses with an equivalent focal length of less than 24mm. With such a wide angle of view, these lenses allow you to fit an astonishing amount of your scene into the frame. However, this can bring with it a certain amount of distortion. As such, these lenses are usually reserved for more specialist uses, such as close-up sports and action, point of view (POV), grand interiors, or extremely large scenes such as the night sky.

Fujinon Ultra Wide-Angle Lens Examples:

X Series: XF8mmF3.5 R WR, XF14mmF2.8 R, XF8-16mmF2.8 R LM WR
GFX System: GF23mmF4 R LM WR, GF20-35mmF4 R WR

 

What Is a Wide-Angle Lens?

Focal length (35mm equivalent): Between 24mm and 35mm
Angle of view: Between 84° and 63°
Great for: Landscape, astro, architecture, interiors, action, group portraits
Not so great for: Individual portraits, wildlife

Wide-angle lenses are lenses with an equivalent focal length of between 24mm and 35mm. They offer a wide angle of view that makes it possible to fit a large amount into the frame, while avoiding the distortion of perspective that can be experienced with ultra wide-angle lenses. This balance makes them a firm favorite for photographers who want to frame sprawling panoramas, towering skyscrapers, or tight interiors. They are also excellent for erratically moving subjects.

Fujinon Wide-Angle Lens Examples:

X Series: XF16mmF1.4 R WR, XF18mmF2 R
GFX System: GF30mmF3.5 R WR

 

What Is a Standard/Normal Lens?

Focal length (35mm equivalent): Between 35mm and 70mm
Angle of view: Between 63° and 34°
Great for: Documentary, street, portrait, landscape, travel
Not so great for: Wildlife, sports, architecture, interiors

A standard or normal lens is a lens with an equivalent focal length of between 35mm and 70mm, adopting an angle of view close to that of the human eye. This focal length is favored by documentary and street photographers because it achieves the most true-to-life depiction of the scene at hand. Such a natural angle of view means standard lenses are extremely versatile and, as such, can lend themselves to a variety of genres.

Fujinon Standard Lens Examples:

X Series: XF27mmF2.8 R WR, XF33mmF1.4 R LM WR, XF35mmF2 R WR
GFX System: GF45mmF2.8 R WR, GF55mmF1.7 R WR, GF80mmF1.7 R WR

 

What Is a Mid-Telephoto Lens?

Focal length (35mm equivalent): Between 70mm and 135mm
Angle of view: Between 34° and 18°
Great for: Portrait, macro
Not so great for: Architecture, interiors

A mid-telephoto lens is a lens with an equivalent focal length between 70mm and 135mm. Mid-telephoto lenses are particularly favored by portrait photographers because of their flattering angle of view. Additionally, higher magnification allows photographers to stay an unobtrusive distance from their subject for more natural results. It also helps to create beautiful, blurred backgrounds that ensure subjects stand out in the frame.

Fujinon Mid-Telephoto Lens Examples:

X Series: XF50mmF1.0 R WR, XF80mmF2.8 R LM OIS WR Macro
GFX System: GF110mmF2 R LM WR, GF120mmF4 R LM OIS WR Macro

 

What is a Telephoto Lens?

Focal length (35mm equivalent): Between 135mm and 400mm
Angle of view: Between 18° and 6°
Great for: Portrait, sport, wildlife
Not so great for: Architecture, interiors, everyday

A telephoto lens is a lens with an equivalent focal length between 135mm and 400mm. A higher magnification allows you to frame a scene from a distance, which is useful when you want to document a moment without influencing it. They are also excellent for picking out specific details from wider scenes and, by compressing perspective, they can create remarkable separation between a portrait subject and their background.

Fujinon Telephoto Lens Examples:

X Series: XF50-140mmF2.8 R LM OIS WR, XF200mmF2 R LM OIS WR
GFX System: GF250mmF4 R LM OIS WR

 

What Is a Super Telephoto Lens?

Focal length (35mm equivalent): Over 400mm
Angle of view: Less than 6°
Great for: Sport, wildlife, astro
Not so great for: Architecture, interiors, street, documentary

A super telephoto lens is a lens with an equivalent focal length of over 400mm. With such a high magnification, these lenses are perfectly suited to framing scenes that are impossible to get close to. Examples might be an animal hunting in the wild, a player scoring at the opposite end of a sports field, or the moon in the night sky.

Fujinon Super Telephoto Lens Examples:

X Series: XF200mmF2 R LM OIS WR + XF1.4X TC F2 WR, XF150-600mmF5.6-8 R LM OIS WR

Prime vs Zoom

Hopefully by now you have a good idea of what focal length is, how it affects angle of view, and indeed how it can best be utilized. But even with this knowledge, it can still be hard to decide which focal length is best for you.

In that situation, you may wish to consider a zoom lens instead of a prime lens because a zoom lens combines lots of different focal lengths options into one.

After reading that alone, you may be curious as to why anyone would choose a prime lens in the first place, but there is more to consider when choosing between the two. Read on to understand the differences between each one.

What Is a Prime Lens?

image of FUJINON GF55mmF1.7 lens

A prime lens is a camera lens with a fixed focal length, which means it does not zoom in or out optically.

Because prime lenses only utilize one focal length, they require fewer internal lens elements and there is no space taken up by complicated zoom mechanisms. This means in some cases they can be smaller, lighter and faster. Additionally, with less glass for the light to travel through, some offer higher image quality.

However, only one focal length can be restrictive when out in the field, which means you would need to carry a selection of prime lenses with you to achieve the versatility of a zoom. Not only can this be cumbersome, it can also be time-consuming having to change between lenses.

What Is a Zoom Lens?

Close up of zoom ring on FUJINON lens

A zoom lens is a camera lens with a variable focal length, which means it is possible to zoom in and out optically.

Because zoom lenses combine many different focal lengths into one lens, photographers can enjoy versatility without having to carry multiple lenses around with them. Furthermore, selecting a different focal length is as quick and simple as twisting the zoom ring, as opposed to switching lenses altogether.

The internal construction of zoom lenses is more complicated than prime lenses because they require additional lens elements and zoom mechanisms to accommodate the different focal lengths offered. This often makes them larger, heavier, and more expensive than prime lenses. For many photographers, that is a small price to pay for the convenience.

For example, many zoom lenses transcend the focal length categories outlined above, meaning they can be just as good for landscape and architecture as they are for portraits and even wildlife.

Furthermore, modern zoom lenses are very similar in size and quality to their prime counterparts. Check out XF16-80mmF4 R OIS WR, XF18-120mmF4 LM PZ WR, and XF70-300mmF4-5.6 R LM OIS WR from the XF Lens lineup.

Learn more by exploring the rest of our Fundamentals of Photography series, or browse all the content on Exposure Center for education, inspiration, and insight from the world of photography.