What is Focal Length?

In photography, focal length is a measure of the distance between the center of the lens and the camera’s main focal point, which is usually on the camera’s film or image sensor. In layman’s terms, focal length refers to how much of a scene your camera takes in. The focal length is measured in millimeters, but can affect targets several hundred meters away. The three most common focal length groups are wide angle, normal and telephoto.

Wide-angle refers to any focal length below 50 mm, or 40 depending on the image’s size and diagonal. Ironically, wide angle is the one that most accurately represents the way people see. Normal is essentially a focal length of 50 or higher, up to approximately 90 mm or so. Like with a wide-angle, normal focal length is not static. Telephoto is probably the best known of the three. Measured at 90 mm or more, telephoto lens magnifies distant objects. Be warned, not every focal length setting is ideal in the situation that you are in or the shot that you want to take. For example, even if you were to use wide angle, normal and telephoto to shoot the same object, perspective and angle would be different for all three. Generally, longer focal lengths are used with higher shutter speeds.

In photography, there are two focal lengths to consider, the front focal length and the back focal length. These two measurements are unique to the lens being used, but, generally, have the same meaning across various lens types. The front focal length refers to the distance from the front cardinal or focal point of the lens to the apex of its primary plain. The back focal length refers to the space between the rear/back focal point and the apex of the last plain of the lens.

Just to be clear, you can change the focal length of a camera without changing the appearance of the objects in the foreground. You can always change the camera’s distance to whatever your target is. However, by adjusting the focal length to account for this shift, you are, in effect, changing the apparent distance of objects in background. Basically, by changing the focal length, you are able to alter someone’s perception, which has a huge impact on art and people’s worldview. For example, using different focal lengths, you can make a person appear closer to the foreground than what they actually are, which will draw more attention to them. Just a simple change in length is enough to make an “innocent bystander” become a main part of the action up front. Focal length is without a doubt, one of the most important elements of photography, one that, when mastered, will give the user great control of perception and depth