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There is a great relationship between focal length, compression of space and depth of field. Knowing what those relationships are, how they work and what creative things you can do with them, is key to a finished product that is deliberately made and have the most effective communication. In this lesson we will show you what those relationships are along with the more typical uses of each focal length category.
Lenses with different focal lengths can have dramatic effects on how space is portrayed in your shot. Normal lenses will mimic a natural experience of depth in your shot. The distances between objects and movement toward the camera will translate closely to how the human eyes see them.
Wider lenses stretch space out, exaggerating depth and the distance between objects, making them appear much further apart than they are in real life.
This will also make movement coming toward the lens appear much faster than we expect, and this appearance of “covering more ground” will be more exaggerated and a subject gets closer to the lens.
Telephoto lenses compress space, removing depth cues that help the viewer distinguish the distance between objects in a scene. This can make a scene feel more intimate, or even claustrophobic depending on the subject matter. Any movement toward the lens is compressed, and feels like a it takes longer than normal to cover a given distance.
While wider lenses do accentuate depth, it’s a common misconception they also suffer more from perspective distortion than telephoto lenses. In reality, this distortion is equal if a subject is placed the same distance from a telephoto and wide angle lens. However, because a subject is typically placed much closer to a wide angle lens to achieve the desired framing, you see this distortion revealed much more often when a wide angle lens is used.
One key factor that the focal length of a lens effects is the depth of field in your shot. The depth of field refers to how much of your shot is in and out of focus. A deep depth of field has a wide area in focus, and conversely, a shallow depth of field has a narrow area in focus.
The focal length of a lens has an inverse relationship to the depth of field in your shot. If the f stop and subject distance remain constant, a lens with a shorter focal length will have a deeper depth of field, while a lens with a longer focal length will have a shallower depth of field.
There are no hard and fast rules for what focal lengths can and can’t be used for a given shot. Ideally, the focal length you choose will be dictated by how you want your shots to look. But of course, many times it might be dictated by logistics like a cramped shooting location or a subject that you can’t get close to. Now that we’ve given the disclaimer, here are some common scenarios and typical focal lengths choices.
Now if you are shooting a single person interview, choose a 35mm and you will be able to work in tight spaces, however it can make features look a bit unnatural depending on how tight your framing is.
If you're shooting portraits, the go to lens is a 85mm, as it’s the standard portrait lens.
You’ll find it's pleasing to feature on face, but you need space to use it and it will hide more background.
If you want to emphasize a subject in foreground use wider angle or if you want to compress all object into one, use telephoto.
Now that you understand the relationships between focal length compression, depth of field and common uses for each focal length, you will be able to choose the right tool for any job. Being able to make what you see in your creative mind and turn it into the right technical choices to achieve your goal will improve your story and overall production.