Cinema School: Lesson 2 – Exposure and Lighting

What is noise?

Have you ever seen a poorly lit video with grainy randomly moving particles in the dark areas of the image?  Perhaps the particles were even visible in the brighter areas as well. These particles are visual noise. They are the by-products of poorly exposed shots.  The less light a scene has the more likely noise will be produced in the background of the image.

Many filmmakers are obsessed with getting very moody images in-camera. They want to maximize dynamic range and have shots that go from extremely dark to extremely light.  Or perhaps, they seek to create eerily dark scenes with one light or sometimes no lights.

There is nothing wrong with wanting to control the look of your image during production. Getting as close as you can to the final image in-camera can save you a lot of post-production time. Unfortunately, starving the sensor of light and underexposing can often be less beneficial than properly exposing the image and adjusting the look.

Exposure

Exposure is the amount of light (controlled by the aperture) captured over a very specific amount of time. 

Another way to define it is exposure refers to the amount of light that is let into the camera sensor. The more light received, the brighter the image. Conversely, the less light received, the darker the image.

While the camera producers will often talk about how many stops of dynamic range a specific camera has, the amount of really usable information typically resides within a much smaller range. 

For Digital Cameras you typically want to try to fit everything within 2 stops above or below perfect exposure. 

Anything more than two stops over may risk being overexposed.  This overexposure will result in a loss of image detail in the brightest areas of the photo.  Anything less than two stops under could possibly be underexposed.  This will result in the introduction of noise. Of course, this also depends on the camera you are using. Some cameras have much more latitude in either underexposure, overexposure, or both.

Aperture

The aperture, also known as F-stop, controls how much light hits your camera’s sensor or basically the size of the opening in the lens when a photograph is taken.

A higher aperture setting means less light is being allowed into your digital sensor.  While a lower aperture setting means more light is allowed into your digital sensor.

ISO

The ISO setting can affect the brightness of the image by digitally altering the brightness of everything in the image.  This comes at a price, as raising the ISO introduces noise and degrades the quality of the image.

Shutter Speed | Shutter Angle

Shutter Speed or the Shutter Angle of a camera for video is typically locked at 180° or 1 divided by double the frame rate used. This was a practice that started to mimic the amount of motion blur seen in film-based motion pictures with a mechanical shutter.

Example: 24 fps would have a 1/48 second Shutter Speed setting.

As such, while the Shutter Speed | Shutter Angle can be modified to increase or decrease the brightness of a scene, it does so at the expense of the motion cadence of the image.

Example: 1/40 shutter or a 216° Shutter angle would increase the brightness of the scene by a third of a stop, but it would also introduce a bit more motion blur in the image.

Proper Exposure

What is proper exposure? Proper exposure is composing or capturing a scene that is not too bright or too dark for image details to be clearly seen without extreme loss of detail through overexposure or underexposure.

An overexposed image will have areas of the photo that are blown out or too bright for details to be seen.  There is usually very little image detail in the overexposed areas of the picture.

An underexposed image will have areas of the photo that are too dark for details of the image to be clearly seen. When the image is brightened in post-production noise will often muddy or obscure detail.

A better approach for both overexposure and underexposure is to light the image for maximum detail and create the mood you seek in post. That said, you can still manipulate the scene to be as close to your final image. You just need to do it in a way that allows you the greatest amount of flexibility.

The best way to manage the exposure of a scene is through proper set design and controlled lighting. 

For example: Let’s say you are lighting a very moody scene in a haunted house.  The main character is holding a flashlight.  Many novice directors or cinematographers would want minimal light to convey the eerie darkness of the scene.  This is a mistake.

It’s far better to light the scene properly while accenting it in the direction you want. In this case that may mean getting enough light on the characters and the parts of the background you want to highlight, but allowing other areas to be slightly darker. You would then employ a super powerful flashlight, and slightly lower the light in the path of the beam to aid in its visibility.   

Beginning Lighting Setup

When lighting an interior scene it is often best to begin with a 3 point light set up featuring:

1- Key Light:  This is the main light studio light that gives the majority of the lighting to the subject.  It is usually set up at an angle toward the face of the actor you wish to shoot, but on the opposite side of the camera.

2- Fill Light:  This is a light used to fill in the shadows left on the subject by the Key Light.  It is less intense than the fill light.  It lightens shadows enough to illuminate the subject while allowing enough shade to provide contrast.

3- Backlight: This light is typically overhead and behind the subject.  It provides a sort of rim or halo to the silhouette of the subject, giving it depth.

This is only your basic lighting setup. If you stick with just three-point lighting your scene will be bland and lifeless. This is where art design and creativity come into play. It is also where you need to have a bit of lighting knowledge.

Example: You’re lighting a scene with a woman sitting at the table reading a book by candlelight. You would like to be able to see her face, her actions, bits and pieces of the background, as well as give the illusion of candlelight.

If you lit the scene with candlelight by itself the image would be underexposed. You could, however, create a key light coming from the general direction where the audience would perceive the candle casting a light.

Your fill light and backlight would be subtle enough for her to be made out but not bright enough that it would distract the audience from the scene.  Your background light would shine on the part of the background that you want to show, but it too, would, from the basic direction of the light the candle is supposed to be throwing.

Now, let’s keep in mind what we learned earlier. There must be enough light for the shot to be exposed properly. It is far better to bring down the brightness of the shot in post-production than to introduce noise to the shot through underexposure. 

Putting it all together

Begin each scene with one light.  This is typically the practical light that will be viewed by the audience as the source light.  Once you have established this light you can then set your key, back, and fill light. 

After those lights have been established you can stylistically choose what parts of the scene you want to feature. There are no limits other than the limits you impose upon yourself.