focus puller of a cinema camera in action
Source: https://lensnotes.com/cine/focus-puller/

Our eyes are designed to always lock our focus on an object or a human face. We humans have been training since childhood to perfect the technique of focusing our eyes. When you are young you can keep reading a book while your eyes are focused up close and when you look away your focus changes very quickly within milliseconds. 

In the cinema industry when they start developing the video cameras they have integrated these principles so that the footages that come out of them look more natural to the naked eye.

If we think about the limitation of the technology of these cameras, it's our boundaries of vision, because there's no point in improving these cameras beyond the limitation of human vision. So the current industry is focusing more on making the footage that comes out of cameras to looks more natural to the naked eye rather than making them more high spec. ( like the higher resolution footages that created by cameras today won't even be noticed by the human eye)

close up of pixels of a iphone screen
you have to look close enough to see the pixels


Example of this would be the idea of Steve Jobs co-founder of Apple, he once said in a keynote that 
Apple had stops improving the resolutions in I-phones displays because the current resolution( 326ppi pixels per inch), will be imperceptible to human eyes and it is the limit of the human retina, so he called it retina-display.

Cinematography

So Let's come to Cinematography, where camera technology and the use of depth of field really matters and have a great impact on the cinema industry.

Focus and The Depth of Field


Focus - What we can see in the scene.
Depth of Field - How much depth back to forth we can clearly (in focus) see.

Focus

In a movie, the director uses focus to control the audience's attention. if he wants the audience to look at a person or an object more closely he would focus the camera on that point. That element would be called the Focal Element of the scene.

It doesn't necessarily want to be the camera focus in creating the Focal Element of the scene, it can be created using the contrast of colors, like in the following picture, you can see the Subjects naturally stands because of the contrast of colors the director has used in the scene.

contrast colors in movie shots

Dept of field (How deep you want the attention of the audience to be)


Depth of field is now a commonly used technique in Cinematography and Photography and it's been used every movie platform unless it's 2D or cartoon which they cannot express the depth because the 3rd dimension is not there.

The deeper depth of field

This technique commonly used when the director wants to narrow the focus of the audience to a subject, commonly used for faces and sometimes objects as well. It's another dimension to the storytelling process. When the character is expressing strong emotions,  adding a higher depth of field and isolating the character from the background makes the scene more powerful.

source: Joker 2019 © DC Comics

In the above shot taken from Joker one of the best movies in 2019 using the depth of Field cleverly, here the joker looking at the people (rhetorically the society) whos treating him differently and the main reason the Joker becomes Joker.

The Flat image (No depth of field)

Commonly used to indicate that's something special going to happen to the character after this bland, quiet period. It adds temptation to a scene, like leading up to something interesting in the story. It can be used as an interval period for the audience to catch up with the story and think about the past and future of the story. Like CGI, If the technique is used well you won't even notice it.
 

© Fox Searchlight Pictures: The Grand Budapest Hotel


In previous articles, I have talked about the Composition in Cinematography Part 01 / Part 02
You can read those articles to get an idea about how all these little components come together to make a great piece of art.