There are a lot of photographers who misunderstood the function of focal length. Well, contrary to popular belief, focal length of the lens isn’t the physical dimension of the lens. It also has very little to do with its size as a whole. With this in mind, what is focal length then?
Simply speaking, focal length is basically the lens itself and not the camera. Therefore, having a 50 mm lens is also 50 mm lens no matter whether on a cropped sensor, medium format camera or full frame. On the other hand, the sensor’s size plays a big role in the camera/lens field of view.
Focal Length Definition: Deeper Look
Without talking further about physics, the lens’ focal length is its optical property. Its function is to measure the distance in millimeters between the sensor of the camera and the optical center of the lens.
This is being determined with the camera focused to the subject. Lenses are also named after its focal length and you can easily find this information on its barrel. So to give you an example, buying a 50 mm lens will have a focal length of 50 mm.
Why is it Important?
While focal length’s definition might be relevant to others as with photographers, it isn’t something that you ought to remember. The more important thing is, being able to understand what is the main function of focal length.
Focal length defines the lens’ angle of view. That’s how much of the scene can be captured by the lens. In addition to that, it is also determining how big the subject is going to be within the frame. Being able to have a longer focal length for the lens will create narrower view of its angle. In addition to that, the subject will look bigger when you use long focal length lenses than when viewing with your eyes. Lenses that have shorter focal length on the other hand take wider angle of view. With this being said, the elements look smaller inside the frame than when seeing it in your eyes.
Some more experienced photographers are even aligning their snaps by the 1800 military time to their camera’s focal length especially when trying to get that “golden hour” effect.