The focal length tells us the angle of view determining how much of the scene will be captured as well as the magnification. It is the optical distance from the point where the light meets inside the lens to the cameras sensor and is usually measures in mm.

Lenses that have a shorter focal length will have a larger depth of field.

55mm

35mm

24mm

55mm

35mm

24mm

18mm

All of these photos were taken in the exact same position with a tripod, making the only difference in these photos the focal length. 55mm was the longest focal length available on the camera. As you can see from the photos the pictures taken with the focal length of 55mm more of the scene was captured showing jasmine and all of the background. As the focal length gets shorter such as 18mm there was less of the scene captured making jasmine the main subject with less background.