Focal length
Focal length is one of the basic concepts of photography. To visualize focal length, simply take a camera and move the zoom from a direction to another. Each time you zoom in, you are in fact increasing focal length. Each time you zoom out, you are decreasing focal length.
Focal length is measured in mm, and is technically the distance between the optical center of the lens and the film (or sensor) plane that allows focus for objects at infinite distance.
Practically, changing focal length will change the angle of view that you capture when taking a photo. Alternatively, one can also say that by changing focal length, you change the size of the objects within the photo.
Let’s see this in a simple illustration:
Focal length is measured in mm, and is technically the distance between the optical center of the lens and the film (or sensor) plane that allows focus for objects at infinite distance.
Practically, changing focal length will change the angle of view that you capture when taking a photo. Alternatively, one can also say that by changing focal length, you change the size of the objects within the photo.
Let’s see this in a simple illustration:
And in real world
Now a question for you to answer:
· Is increasing focal length equivalent to getting closer to the subject?
Well, the illustration below show that the answer is no.
When you zoom in (increase the focal length), the relative dimension of all subjects increases in a linear way: the perspective is the same. When you get closer, you are changling the perspective, and the relative size of objects change
· Is increasing focal length equivalent to getting closer to the subject?
Well, the illustration below show that the answer is no.
When you zoom in (increase the focal length), the relative dimension of all subjects increases in a linear way: the perspective is the same. When you get closer, you are changling the perspective, and the relative size of objects change
Below are three real photos that illustrate this difference. As you can see, when you get closer, you are changing perspective. The relative size of objects change, and farther objects appear smaller. On the other hand, when you zoom in, you are keeping the same perspective, and just getting objects larger. It is exactly like cropping the final photo.