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Focal length Explained

How does the lens you choose affect your image ?

· Filmmaking,Photography,lenses,video

What is focal length ?

Focal length is usually represented in millimeters, it is one fundamental ways to describe a lens. Focal length is a calculation of the optical distance from the point where light rays converge to form a sharp image of an object to the focal plane in the camera.

Effects of focal lengths

The focal length of a lens tells us the angle of view (how much of a scene will be seen) and the magnification (the size individual elements will be). Long focal lengths have a narrower angle of view and higher magnification. Short focal lengths have a wider angle of view and lower magnification (see below).

It is really important to understand that different focal lengths will have very different effects on the overall aesthetics of captured images. There are three effects are commonly considered most important:

  1. Depth of field
  2. Compression of space
  3. Three-dimensional feel of the resulting two-dimensional image

A longer lens will compress space, to say that objects in the background will appear much bigger and closer than they actually are. This compression will also affect the three-dimensional feel. The resulting image will look relatively flat compared to the look of a wide angle lens .

The examples below show the exact same framing on the foreground object all six images differ greatly in terms of background compression.

The dartboard in the background looks very big when shot with the 135mm lens, as if the plushie is located close in front of the dartboard. Meanwhile, with the 14mm, you can’t even see the board. The background, looks further away and adds a feeling of more space to the frame.

-2 videos with great explanations about focal length-

Zoom or Prime Lens

There are two types of lenses, they are called prime and zoom lenses. Prime lenses have a fixed focal length and zoom lenses have variable focal lengths.

A zoom lens is very versatile. They are ideal when shooting a variety of subjects in a small period of time such as landscapes or people. Using a zoom lens reduces the number of times you need to change the lens which saves time. Zoom lenses are all about convenience.

The main advantages of prime lenses are their size, weight as well as their maximum aperture or f/stop and sharpness. Prime lenses also tend to have a larger maximum apertures than zoom lenses. This is an advantage when shooting in low light conditions as it will increase the possibility of having a clean image. Using prime lenses with large apertures also means you can get a shallow depth of field which is a desired look in filmmaking. Prime lenses are sharper than zoom lenes as there construction is more simple and uses less glass thus less room for imperfections.

Choosing a lens

Price and versatility

Price is an important factor when choosing the lens as for most of us it would be too expensive to rent lenses for every shoot. 

Normally zoom lenses are the most well rounded.  As you have a variety of different focal lengths in one lens. A 24-70mm could be a great way to start to test different focal lengths so you can find your style.

Prime lenses tend to have a higher image quality a good starting off place would be to have a 50mm and 35mm lenses with a relatively fast apertures f1.4, f1.8 or f2.

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