Filmmaking Basics part 2: Setting Exposure


To get a useable image that isn't to bright or to dark, you need to control the amount of light that reaches the sensor. In other words, you need to set the exposure. In photography and video, there are three main controls to adjust the amount of light:

  • Your camera's shutter speed
  • Your lens' aperture
  • Your camera's ISO

These three work in conjuction to limit (or boost) the amount of light reaching the sensor, but each of those settings have their own unique 'side effects' on your image. For example, the aperture not only affects the brightness of your image, but also changes how much of your image is in focus. So you can use your aperture to get a blurry background, or conversely: to get everything in the shot in focus. If you understand how each of those three settings affect your image, you can really get creative with any camera!**

This is going to be an introductory article, so if you already know the basics, feel free to skip ahead or jump to the quick reference.

Shutter speed

What does it do?

Shutter speed determines how long the light hits your sensor, measured in fractions of a second (e.g. 1/50, 1/200, etc.).

Side effect

As a side-effect it also determines the amount of motion blur. Our eyes have been trained to expect a certain amount of blur whenever someone or something moves in films. To get that natural-looking motion in your shots it's best to stick to the so-called '180 degree shutter rule': your shutter speed should always be double your frame rate. For example, if your frame rate is 25 frames per second, your shutter speed should be (2 x 25 = ) 1/50th of a second.

While you could break this rule for dramatic effect, a faster shutter speed leads to jarring, restless motion (as if there are frames missing from your footage). If you use a longer shutter speed, your actors will look like ghotly figures that leave behind a trail of blurs.

Shutter speed explained

Aperture

What does it do?

The aperture determines how much light hits the sensor, measured in f-stops. The aperture is a ring inside your lens, that can open up to let in more light, or close down to let in less light. Very much like your eyes' iris.

Side-effect

A nice side-effect of the aperture is that it also determines how much is in focus in your shot. If you open the aperture to let's say f/1.8, not only will there be more light falling onto your sensor, only a small part of your image will be in focus. On the other hand, if you close down the aperture to f/11, everything in your shot will be in focus.

This way, you can really use the aperture creatively: open your aperture for those creamy blurry backgrounds and draw the viewer's attention to your subject, or close it down to show all of your subject's surroundings.

Note: the confusing part about aperture is that opening the aperture to let in more light, equals a low number (e.g. f/1.8 or f/1.2) while closing the aperture equals a high number (e.g. f/22)

Aperture explained

ISO

What does it do?

We'll end with the most straightforward of the three: ISO. ISO determines how sensitive your sensor is to light. In the analog film days you would have different film stocks with different sensitivities, but luckily on digital cameras you can adjust the sensitivity without changing your film stock ;-)

Side-effect

The higher your ISO, the more noise gets introduced into your image. While most modern cameras can handle higher ISO's with ease, it's still a good idea to test what ISO setting you find acceptable on your camera.

ISO explained

Quick reference

To sum up, here's a quick reference chart:

Name What does it do? Side-effects
Shutter speed How long does the light hit the sensor? Motion blur
Aperture How much light hits the sensor? How much is in focus
ISO How sensitive is your sensor to light? Adds noise