Unit Two : The Gear
Introduction to Focal Length
Put simply, focal length is what determines how “zoomed in” you are, also often called field of view (FOV). Focal length is an actual length, expressed in millimeters - it corresponds to the distance between the optical center of the lens and the film plane. The lower this number, the less zoomed in you are. You’ll hear photographers use the word “wide” to talk about this because you can see a large amount of the scene. Conversely, if the number is high, the angle will be “narrow,” and you will only see a small portion of what is in front of you. In this instance, you are zoomed in. Being extremely zoomed in is referred to as “telephoto.” Some lenses, called “zoom lenses,” allow you to change your focal length. So-called “prime” lenses are fixed to one focal length.
The choice of a focal length is the very first step in composing a photograph. Focal length determines framing, so in that way, it is one of the most important choices you make as a photographer - every other choice (exposure, depth of field, etc) are dependent on your decision in framing.
Going a Bit Deeper
While simplified, the above is really the need to know information. It does become more complicated, but if you’re not too fussed on the technical intricacies, understanding the idea of focal length determining your FOV is enough.
For those with a more keen interest in the technical aspects, we must note that focal length gets more complicated when you start looking at the actual numbers. An 18mm lens on a medium format camera will produce a very different angle of view than the same focal length on a compact camera. A modern compact like the Sony RX100III has focal lengths between 8.8 and 25.7mm, yet the same values on a lens for a FX DSLR like the Nikon D850 would be exceptionally wide, making for a more difficult scene to compose.
The culprit of this phenomenon is what we call the “crop factor.” The focal length is a physical property of a lens, but the resulting angle of view, which is what we are really interested in, depends on another factor: sensor size. The bigger the sensor, the wider the angle of view for the same focal length. In order to convert angles of view between different formats, we use the crop factor, which is a ratio between the standard 35mm film area and the actual sensor size. For instance, Nikon DX cameras have a smaller sensor than their FX counterparts, which results in a 1.5x crop factor. This means that a 28mm lens on a DX camera will have the same angle of view as a 28*1.5=42mm lens on FX.
Of course, this works in the other direction too: if your sensor is bigger than 35mm film, then you will need longer focal lengths to obtain similar angles of view: on 4×5 large format cameras, 150mm is considered “normal”, whereas it would be firmly in the telephoto domain on a DSLR.
Because it can all be a bit confusing, especially with lenses that can be used on several different formats, it is common to give a “35mm equivalent” focal length: the focal length at which a 35mm/FX camera would give the same angle of view.
You just need to be careful when discussing actual focal lengths: remember that the final angle of view (which is probably what you are discussing) depends on the crop factor, and that everyone may be using different ones. This is one of the reasons it may be advantageous to disclose what gear you’re using, so there’s context as to what the crop factor is (or isn’t).
Sometimes, it will be worth getting closer to your subject and using a shorter focal length, if you want to create depth and emphasize perspective. Sometimes, you will have to walk backward and use a longer lens, if you want to compress perspective.
Chelsea London © 2023. Fujifilm X100F | 33.0 mm | ƒ/2.0 | 1/1000s | ISO 200Chelsea London © 2019. Fujifilm X-T1 | 56.0 mm | ƒ/6.4 | 1/180s | ISO 200Fact or Fiction: Distortion and Compression
A common misconception is that focal length has a direct relationship to distortion. Normally this will be demonstrated through a mid-shot - a portrait shot from the shoulders up. That demonstration, shown through .gif or static images, will show a face at 18mm, 56mm, and 80mm, for example, and there will be apparent distortion through squished heads and bulbous noses at 18mm, and more natural-looking head shapes and noses at 80mm. You’ve probably already seen this effect in your own selfies. But let’s look at this from a border point of view. Think about that selfie you’re taking. As it’s inherently taken by you, by your own hands, you can only hold the camera so far from your own face. Keeping that in mind, think now about that portrait with an 18mm focal length. We know that 18mm is quite wide, meaning there’s a lot of the scene in that image. To make sure the subject (in this case a person) is seen clearly and not lost in that massive scene, the photographer has to move closer. And closer. And closer. That physical distance between the photographer/camera and the subject is what’s causing that facial distortion. Step back far enough, and the subject’s face is perfectly proportioned. So now think about that 80mm photo - the zoom factor of the focal length allows the photographer to stand further away from the subject, thereby not introducing any facial distortion. Now think back to that selfie - does it reflect what you see in the mirror or photos taken by someone else? No, because the arm’s length you can provide yourself is not far enough away to negate any distortion.
That brings us to compression. The term "compression" is often used to describe the visual effect of narrowing the perceived distance between elements in an image. This effect is related to the choice of focal length and the resulting perspective in the photograph. Like that distortion .gif, you may have seen .gifs or visual representations of compression - normally with a farmhouse or shack in front of mountains. At wider focal lengths, the mountains behind the shack seem small and far away. At more narrow focal lengths, those mountains are massive, and right up on the shack. This “perspective flattening” can be used to a photographer’s advantage strategically.
Sean Makin © 2018. Nikon D610 | 140.0 mm | ƒ/6.3 | 1/15 | ISO 100Sean Makin © 2023. Nikon D610 | 16.0 mm | ƒ/8.0 | 1/6s | ISO 100Focal Length Ranges
Now that you know more about focal length, let’s take a look at the different ranges usually found in lenses, and what their uses tend to be. Of course, there are many, many exceptions, but this is the “normal” use they were designed for. All focal lengths are given for 35mm sensor size (crop factor 1).
Ultra-Wide Angle (14-24mm): They are pretty specialized lenses as they will tend to exaggerate perspective to levels which can easily be disturbing. Our eyes are not used to such wide angles of view, and they will look unnatural, which can be used for artistic purposes. Landscape and architecture photographers love these focal lengths as they will create a lot of depth and emphasize perspective. These can make for cartoonish and fun portrait or action shots - seen sometimes in fashion and skateboard photography. Note that there are lenses even wider than this range, which create even more extreme and exaggerated perspectives.
Wide angle (24-35mm): Wide enough to show a lot of context, but not so wide that they look unnatural, they were used a lot by photojournalists. It is a good “default” focal range, which explains why most kit lenses include them (18-xx lenses on DX DSLRs, for instance).
Normal (40-75mm): What exact length a normal lens should be has been subject to a lot of debate, but it is estimated to be around 45mm. This is an angle of view which looks very natural and “inoffensive”, neither too wide nor too tele. It also corresponds more or less to the focal length we actually perceive (though due to peripheral vision, our eyes have an estimated 22mm focal). Street photographers love these lengths.
Mild tele (85-105mm): This is prime portrait category: long enough to isolate the face and create separation from the background (through shallow depth of field - more on this in another lesson) but short enough that you can still be within communicating distance from your subject.
Medium tele (120-300mm): Just like wide angle, this is a very prevalent focal length which can be used in most genres to isolate details and simplify compositions. For landscape work, remember about the “perspective flattening” effect.
Long and exotic tele (300-800mm): Those are specialized lenses for wildlife and sport photographers who need to get close to their subjects but can’t physically move. They are complex and very expensive lenses, and their angle of view is so narrow that it won’t be of much use to most photographers. Tripods and fat wallets are often required.
All of this is just the tip of the iceberg, but it’s enough to get you thinking consciously about your focal length choices.