When it comes to understanding some of the mots important photography principles out there—one of the most important is undoubtedly focal length. If you are new to the world of photography, this may seem like a foreign term, but it is one that is important to understanding photographs and how they are taken.

Even if you are rather experienced with photography—it is completely natural to have some questions about focal length. In fact, there are some photographers who don’t fully understand the concept of focal length and who are still able to take beautiful photos, but knowing all about this term is important.

If you understand focal length, you will not only gain a better understanding of how to capture the right angle during your photo, but how other elements of positioning and photography come into play as you start to take your own personal photos.

The Definition of Focal Length

The first thing to realize, is that the focal length is not the physical dimension of the lens. In fact, the focal length actually has very little to do with the overall size of your lens.

Instead, the focal length is the optical property of the lens. It is measured in millimeters and goes between the optical center of the lens and your camera’s sensor, or the point of convergence in your lens and the sensor that actually records the image.

This number is also what is used to name your lens.

So, if you have a 150 mm lens—it actually has a focal length of 150 mm. It is right on the barrel of your lens and easy to see. The focal length has entirely to do with the lens on your camera, not the camera itself.

Photographic lenses can vary greatly between 14mm and 600mm-although there are some exceptions. The human eye actually has its own focal length, and is somewhere between 40 mm and 58 mm. This is why 50 mm is typically referred to as the “normal” or “standard” focal lengths.

Here’s how the basic sizes of lenses break down.

• Ultra-Wide Angle: Focal length of 8 mm to 24 mm. Also known as fisheye lenses, they can take in an image of up to 180 degrees around the lens. It does come with some distortion.
• Standard Wide-Angle Lens: Focal Length of 24 mm to 35 mm- This has minimal distortion especially when compared to fisheye lenses, and allows everything to be in focus but seem farther away.
• Standard Lens: Focal Length of 35 mm to 70 mm. This is a versatile lens that can be use in most types of photography.
• Telephoto Lens: Focal Length of 70 mm to 600 mm. Telephoto lenses have a shallow depth of field, and are great for shooting a distant subject and compressing that subject into a background.

Most lenses are ultimately going to fit into one of these four categories.

Focal Length Basics

It is not as important to understand all of the complexities associated with the focal length definition as it is to understand how the focal length applies to taking photos. When all is said and done, your focal length tells you the angle of the view of your lens, or how much is in front of you that the lens is able to capture and how big those subjects are going to appear in your frame.

Focal length is all about your field of view.

The most important thing to remember when trying to determine what photo length is the right photo length for you. The longer your focal length, the narrower your field of view will be. A shorter focal length will give you a wider field of view.

This is the basic concept you should understand when you choose your lens, but there are even more ways the lens can end up changing the look of your photo.

Applying Focal Length to Your Photos

If you are ready to start taking photos and playing with your focal length as you do—you will find that there are a few ways in which the focal length can impact the look, the clarity and the quality of your photos.

Field of View- This is how much of your subject or scene actually ends up in your image as we discussed already. This is the main thing that people think of when they start to choose different lenses.

Depth of Field- When a lens has a long focal length, it typically also has a shallow depth of field, meaning it can focus on small objects at certain distances.  Short focal length lenses on the other hand have a larger depth of field and can get more elements from that scene in focus.

Image Shake- The blurriness that you get in photos from pushing down on the shutter is also known as image shake. A longer lens is going to be more sensitive to this shake, so you will want to swap it out for a shorter lens or use a tripod to get a more clear image.

Perspective- Your lens can also help create new perspective. A shorter focal length lens will give the appearance of more space between your subject and background, while longer focal lenses will give you a more compressed look. This means your subject may look closer to the background than it actually is.

Next time you go to shoot a photo, keep these things in mind as you start taking your images. Swapping out a lens can do a great deal in changing how your final photo comes out.

Focal length can make a major difference in your images and the more you know about the focal length and the different lenses you can use on your camera—the better. This greater understanding of the impact of focal length on your lens can ultimately help you create better and more beautiful photographs that you will be really proud to display.