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This is the third entry in our LL Basics series – a beginner’s guide to shooting film photos.
What is Focal Length?
Focal length is one of the first things to consider when deciding on a new camera and/or lens.
When photographers talk about lenses, the focal length is usually the first detail mentioned in the description of the lens.
For example, when we talk about a 50mm f/1.8 lens, the first part of the lens description – 50mm – is actually just the focal length. (The second part of the description is just the maximum aperture of the lens).
When comparing lenses, focal length has the most significant impact on the shooting experience, so it makes sense that this is the main descriptor used to identify one lens from another.
But what does focal length actually mean?
Focal length is the distance from the film (or the sensor if you’re shooting a digital camera) to the optical center of the lens.
The optical center of the lens is the point where light comes through the various elements of the lens to create a sharp image that can then be recorded to the film (or digital sensor).
Some people mistakenly assume that focal length is just the physical length of the lens itself. In reality, the focal length is a measurement that exists entirely inside the lens.
You can easily find the focal length of any lens – this information is almost always engraved on the front ring of the lens, along with the available aperture.
How Does Focal Length Impact Images
Now that you know the technical definition, let’s look at how focal length actually affects your photos.
There are a few visual aspects that focal length impacts – the angle of view, level of magnification, and compression.
Angle of View
In the simplest terms possible, angle of view means how much of the scene will be captured by your lens.
Shorter focal lengths have a wider angle of view, meaning more of the scene will be captured. This is where the term “wide angle” comes from.
On the flip side, longer focal lengths have a narrower angle of view, meaning less of the scene will be captured.
Level of Magnification
Just as important as the angle of view, the focal length directly influences the level of magnification in an image.
Level of magnification refers to the size of your subject(s) in your final image.
For a lens with a longer focal length and a narrow angle of view, subjects will be larger in your photo.
For wide angle lenses with a shorter focal length, subjects will be smaller in the image.
Focal length also impacts the amount of compression in your image. The amount of compression is what determines the appearance of distance between subjects.
Longer focal lengths create more compression, meaning that subjects appear closer together.
Shorter focal lengths cause less compression, making subjects appear farther apart.
When talking about focal length compression, the distance between subjects is referring only to the distance in relation to the camera.
In other words, compression will not affect the distance of two subjects if they are side by side (but equal distance from the camera).
Compression changes the appearance of distance between subjects that are varying distances from the camera, or subjects that are on different planes.
Different Focal Lengths and What They’re Best For
Each focal length has its strengths and weaknesses – each photographer also finds their preferred focal length(s) over time.
While there isn’t one universal standard for categorizing focal lengths, most people separate them into the following groups.
Super Wide Angle (Shorter than 24mm)
Some people skip the “super” wide angle category and just consider anything shorter than 35mm a wide angle lens.
We make the distinction because shorter than 24mm is where you’re likely to start seeing distortion from the super wide angle of view.
This means that the edges of the image can start to become slightly warped because the angle is so wide.
Lines will not appear completely straight and the perspective is skewed – most times these things are not desirable, but certain types of photography use the distortion as a stylistic choice.
If you’ve ever heard of a fisheye lens, the rounded, distorted effect comes from the super wide angle of view – fisheye lenses usually have a focal length around 10mm.
Some of the best applications for super wide angle lenses would be:
- Landscape Photography
- Interior / Real Estate Photography
- Events / Settings with Limited Space
Wide Angle (24mm – 35mm)
A traditional wide angle lens will have a bit longer focal length, making it more versatile.
Distortion is much less frequent in the 24mm-35mm range and the narrower angle of view means that you won’t have to get as close to your subjects.
Some photographers use a wide angle lens as their everyday carry. The wide angle of view is a safe bet for almost any subject – longer focal lengths might be too narrow, making it difficult to capture your subject in the way you want.
Wide angle lenses are great for:
- Landscape Photography
- Architectural Photography
- Street Photography
- Everyday Snapshots
- Documentary / Photojournalism
Standard (35mm – 55mm)
It’s commonly said that 50mm is roughly the same focal length that the human eye sees. That’s why we consider around 35mm-50mm to be a “standard” focal length.
Most SLR film cameras came standard with a 50mm f/1.8 lens. This focal length/aperture combo is often referred to to as a “nifty fifty” and is usually recommended as the best type of lens for beginners in film photography.
Standard focal lengths are great for most types of photography which has made them the most popular type of lens.
If we had no idea what we were going to be shooting, we’d definitely choose a standard focal length.
Standard focal lengths are used for just about every type of photography, but some situations where it’s best include:
- Portrait Photography
- Landscape Photography
- Urban Photography
- Everyday Snapshots
Telephoto (70mm or Longer)
The term “telephoto” is commonly used to describe any lens with a long focal length. Some people consider telephoto lenses only 85mm or longer, others put anything longer than 55mm in the same category.
The technical term is even more complicated – a true telephoto is a long focus lens where the focal length is longer than the physical length of the lens.
Whichever definition you choose to abide by, the same is true – a telephoto lens has a much narrower field of view with a lot of compression.
Focal lengths around 85mm are considered to be the most flattering for portraits because this length shows almost no distortion. When your subject is a human face, even slight distortion can cause odd effects on their facial features.
Another benefit of telephoto lenses is that you’ll get a lot of background blur, making your subject pop. Telephoto lenses are great for:
- Portrait Photography
- Wildlife Photography
- Sports Photography
- Product Photography
Prime Lenses vs Zoom Lenses
There are two main types of lenses for photography – prime lenses and zoom lenses.
The difference is simple. Prime lenses have one, fixed focal length. Zoom lenses have a range of focal lengths that the lens can move between.
There’s no doubt that zoom lenses are much more versatile – so why do so many photographers choose to use only prime lenses? There are a few benefits:
- Prime lenses usually have a larger maximum aperture.
- Prime lenses are generally more compact and lighter.
- Prime lenses tend to produce sharper images.
- You need to be more thoughtful about your photos with only one focal length available.
Film photography tends to skew much more in favor of prime lenses. Zoom lenses for film cameras were a bit more niche than they are for digital cameras.
As we said previously, most film SLR cameras came standard with a prime lens (usually a 50mm). On the flip side, most digital SLR cameras came (and still come) standard with a zoom lens (usually 18mm-55mm).
Now don’t get us wrong – it’s not that prime lenses are explicitly better than zooms. Each type of lens has its strengths and weaknesses and the specific use will determine what is the best choice.
Photographers tend to choose zoom lenses because:
- Zoom lenses are the most versatile, some covering a huge range of focal lengths.
- The cost of lenses can add up, so it’s nice to just buy one zoom instead of multiple primes.
- You’ll need to change your lens much less frequently with a zoom.
It really depends on what type of photography you’re interested in. The versatility of a zoom lens might be a top priority for someone like a photojournalist who needs to be prepared to shoot a variety of subjects without any notice.
What is Crop Factor?
While everything we’ve discussed so far is relevant to both film and digital photography, crop factor is also a consideration for digital cameras.
The idea of crop factor wasn’t much of an issue prior to the digital camera revolution. Almost everyone shot 35mm film, which is always the same size, so this made focal length somewhat universal.
As long as the film size and focal length are the same, you’ll see the same field of view when looking through any camera. When you change the size of the film (or digital sensor), this changes things.
Crop factor is a measurement of how magnified the focal length of a camera will appear, in relation to using 35mm film. Don’t worry, it’ll make more sense when we look at an example:
The most popular sensor format for digital cameras is called APS-C, which has a crop factor of 1.5x.
This means that when you look through an APS-C camera, no matter what lens you’re using, the focal length you’ll see will be 1.5 times closer than if you were using the same lens on a 35mm film camera.
For all intents and purposes, the focal length you see engraved on the front of a lens is the length when using 35mm film.
So, you can use a digital camera’s crop factor to calculate the corresponding focal length, also called the 35mm equivalent. If you ever see this term, it just means: what the length would be if you were shooting 35mm film.
Let’s say you’re using a 50mm lens on a digital camera with an APS-C sensor.
50mm x 1.5 (APS-C crop factor) = 75mm working focal length. You could also say that it has a 35mm equivalent focal length of 75mm.
Full Frame Digital Cameras
The idea of crop factor isn’t relevant to all digital cameras, though. Many high end / professional digital cameras utilize what’s called a Full-Frame Sensor.
These sensors are called “full frame” because they are the exact same size as a standard 35mm film photo – 24mm x 36mm.
Since they share the exact same dimensions, the focal length will be the same on a 35mm film camera as it will be on a full-frame digital camera.
Medium Format Film Cameras
Medium format film is much larger than 35mm film, so this means that, again, the focal length listed on the lens will appear differently for medium format than it will for 35mm.
Unlike digital sensors which are usually smaller, medium format’s large physical dimensions mean that you’ll see a focal length that appears farther away.
For example, a 6×7 medium format has a crop factor of 0.5x. No matter what lens you use on a 6×7 camera, the focal length will appear half as close as if you were shooting 35mm.
50mm x 0.5 (crop factor) = 25mm equivalent.
As such, a 90mm lens on a medium format camera is considered a “standard” focal length. Depending on which medium format you’re using, this is equivalent to a 40mm – 50mm length on 35mm film.