In photography or cinematography, light is what allows you to be able to recreate an image, whether it be digitally with a modern sensor-based camera, or in the analog system by using film. The term “exposure” derives from the original method of capturing images in which film, or a similarly behaving material, was exposed to light, causing a chemical reaction which would replicate what was in view of the camera lens. In order to properly capture these images, it was important to make sure that the amount of light entering the camera was balanced with how quickly it was being taken, and the level of response the chemicals had to the light being captured, to attain correct exposure. This is the basis of the pyramid of exposure, an essential concept for filmmaking, and learning how each of them affects the other two is imperative for any filmmaker, cinematographer, or photographer. It is important to understand the fundamentals of the functions of camera settings and the way light can affect their abilities in order to properly execute one’s artistic vision to the fullest extent. Even a single image can take much work to find the correct exposure, even when following proper beginner’s guide photography tutorials and metering suggestions to find the optimal exposure value and ISO value.
Shutter:
The first point on the pyramid is shutter speed, or shutter angle. Shutter speed, or shutter angle as referred to in cinematography as opposed to photography, is a term used to describe what percentage of a circular disk is covering the film gate. This device is called a rotary shutter. Shutter speed determines the length of time a frame of film, or a camera sensor, is exposed to light for a given frame.
Every time you half or double the shutter speed, or shuttle angle, you have one stop less light coming through. The standard shutter speed for 24fps filmmaking is 1/48 and the standard shutter angle is 180 degrees. These two numbers equate to the same thing, the biggest difference being that shuttle angle is based off of frames per second, while shutter speed is independent of frames per second.
The reason knowing your shutter speed, or shutter angle, is so important is because different settings can have drastic effects on the end result of your image or video. . A slower shutter speed, increasing your shutter angle, or having a long exposure can have the effect of adding motion blur to your image. This should always be used as a creative choice, and not as a way of adjusting your exposure. The opposite is also true, for if you have a faster shutter speed/decrease your shutter angle, your image will have less motion blur which can give a look that is extra crisp. This, again, is a creative choice and should be used as such.
ISO:
The second tip of the pyramid is ISO or ASA. ISO or ASA is how sensitive the film stock or sensor is to light. ISO’s can range from 20 up to 3200, and even higher in some cases. This setting is most commonly set at the “base ISO” for most digital cameras, even though you can adjust this to change your exposure. ISO operates off the same principle as shutter speed. Every time you double your ISO, you gain one stop of light in your exposure, and every time you half your ISO, you lose one stop of light. However when you change the sensitivity of your sensor, you are also indirectly changing the dynamic range of your sensor. It’s not exact, but on average, if you increase your ISO from 800 to 1600, you are also shifting your dynamic range up, so you gain roughly one stop of dynamic range in the highlights, and you lose one stop of dynamic range in your shadows. Generally, a higher ISO will give you more light in an image, and a lower ISO will have decreased light within the image.
Secondly, changing the ISO of your digital camera can add or take away noise in your image depending on the type of digital sensor within your camera. Going lower than the base ISO of your camera can create an extra clean image with even less noise than normal. But on the other end, increasing your ISO can add digital noise to the image. This can be used as a creative choice like in the show Atlanta where the cinematographer shot at an intentionally high ISO, in order to add noise to the image.
Aperture:
The third point of the pyramid is aperture. Aperture is the most flexible part of the exposure triangle. Aputure is a measurement of how much light is allowed through the lens. The scale for aputure goes: 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22. Every 2 stops the f stop scale doubles which is an easy way to remember the scale. Each stop on the lens equates to one stop of light, but opening up on the aperture, also known as going lower on the scale, also will affect your image by giving you a shallower depth of field, meaning the things that are out of focus will be even more out of focus. This again is a creative choice, if you want your subject to feel isolated in the space then maybe you go really shallow with the depth of field, or if you want to showcase the room that your subject is in, and use the objects in the room as a way of telling the audience about your character, you could close down on the aputure so that we see more of the background. Aperture is the most common form of adjusting your exposure out of these three. Because, while it does have some effect on your image. It is less noticeable than adjusting ISO or shutter angle in small increments.
All three of these together create the pyramid of exposure, and are the three basic tools for adjusting your exposure and look for any given project. While each of them can be used to adjust exposure, it is important to understand what effect these adjustments have on your final image. For aperture, it is also changing your depth of field, for shutter speed it is also changing your motion blur, and for ISO it is changing your dynamic range and the noise that will be present in your image. These effects are all important to keep in mind when filming a project because understanding when to use which tip of the pyramid is what will make you a great cinematographer.
Sources:
https://en.wikipedia.org/wiki/Dynamic_range
https://nofilmschool.com/2016/08/how-cinematographer-christian-sprenger-shot-donald-glovers-atlanta