What role does the focal length of a lens play in photography?

The focal length of a photographic lens plays a role in the size of the image and the size of the angle of view. A long focal length produces a large image with a small viewing angle, while a short focal length produces a small image with a large viewing angle. For example, if you want to "zoom in" distant objects, use a lens with a longer focal length; conversely, if you want to push background objects farther away, use a lens with a shorter focal length.

Take the 135 camera as an example: 50mm is the standard lens, 30mm or less is the wide-angle lens, which can capture a wider scene (relatively smaller image); 80-120mm is the medium focal length lens, and 120-150mm is the medium focal length lens. Long focal length lenses, above 200mm are long focal length lenses. If you want to capture the sun full frame, you need a lens with a focal length of 800mm. For head portraits, a 100-135mm focal length lens is appropriate, and for general body shots, a 50-70mm focal length lens can be used.

This illustrates a rule: if you want to make the background closer, you must use a longer focal length; conversely, if you want to push the background farther away and achieve a broader scene, use a shorter focal length lens. You can learn more about the role of lens focal length in photography in the photography forum "Long Photographs the World" Novice Exchange.