Why You Should Know What Focal Length Means
Knowing what the focal length of a lens means in relation to your camera, is very important when it comes to buying lenses. Read this post to find out what different lenses are used for, which ones are right for you, how to use them creatively, and all the technical speak you’ll need.
Lenses are divided into two categories based on whether they can zoom. There are the ones that have a fixed focal length (prime lenses) and those that have a variable focal length (zoom lenses). In general, prime lenses are sharper and often have a wider aperture, great for low light conditions.
Zoom lenses allow you to use one lens to cover a range of different photography fields. One lens means less time spent searching for and changing lenses. There are advantages and drawbacks to both types of lenses, so having a mixture of them gives you versatility and power.
We can use the human eye as an example. Its focal length varies between roughly 17mm and 25mm, depends on who you ask and who’s eye you examine.
We have an approximate field of view of over 180°. This is different from the 90° angle of view from a lens, which is down to the fact that we have two eyes.
What Does It Mean?
The focal length of the lens determines how ‘zoomed in’ your photos are. The higher the number, the more zoomed your lens will be.
It is often misunderstood that the focal length is measured from the front or rear of the lens when, in reality, it’s the distance between the point of convergence in your lens to the sensor or film in your camera.
Different Focal Ranges and What They’re Used For
These lenses are often considered speciality items and not often included as part of a kit lens. They create such a wide angle of view that they can appear distorted. this is down to the lens having to fit more of the scene into film or sensor.
Ultra wide-angle lenses are often used in event and architectural photography. They help to get a lot into a photo when shooting in a confined space. Wide and ultra-wide lenses are about putting yourself in the middle of it all, rather than fitting in the whole of a scene.
Wide Angle 24-35 mm
This is where you’ll find most kit lenses for full-frame cameras start. 24 mm is the point at which the distortion that appears to stretch the side of an image stops appearing unnatural.
They are used by photojournalists for documenting situations. This is because they are wide enough to include a lot of the context, whilst still looking realistic.
Standard 35mm-70 mm
It’s in this range (at about 45-50 mm) that the lens will reproduce what our eyes see (excluding peripheral vision). I like to use this range when shooting on the street or with friends in a closed setting. Examples would be at the dinner table or the pub.
Mild Telephoto 70-105mm
This range is often where kit lenses stop. Here, you’ll start to get into the range of telephoto lenses and portrait primes (around 85mm). This is a good range for portraits as the natural perspective of the lens will separate the face from the background.
Lenses in this range are often used for distant scenes such as buildings or mountains. They’re not suitable for landscape photography because of the way they flatten the perspective of a scene. Lenses in a range higher than this are used for sport and animal photography.
How Does Focal Length Affect the Perspective of A Photo?
I tackled most of this in the previous section. To give you a better idea of how the focal length affects the perspective of a photo, I took four photos of the same subject at different focal lengths and compared them below.
The subjects (three soup cans) remained in the same position (about 10 inches apart from one another) in every photo. It’s worth noting that these photos are shot with a crop sensor. This means the actual focal length will be higher than listed.