EXPOSURE CRASH COURSE

What is Exposure?

Photography is about capturing light, whether it’s on a digital image sensor or a strip of film. Exposure is the total amount of light allowed into the camera to make an image. There are three basic variables that change the outcome of how much light is allowed in - Aperture, Shutter Speed, and ISO.


Aperture:

Aperture is the size of the opening in a lens, which controls the amount of light passing through. Aperture seems kind of counter-intuitive at first. The way Aperture works, the larger the opening, the smaller the number and vise-versa as illustrated by this drawing below.

Cause and effect:

Like the other two variables of exposure, Aperture has a cause and effect. Aperture affects something called Depth of Field. Depth of Field is the distance between the closest and farthest object that appears in focus. If you have a wide depth of field, more will be in focus. If you have a shallow depth of feild, a small amount will be in focus, usually causing background blur, sometimes referred to as “bokeh.”

 

Aperture Examples:

An example for when you would want to use a Larger Aperture (E.G. f/1.4, f/2, f/4) is when you’re in low light and need to allow more light into the camera, or when you want to isolate the main subject from the background.

 

Larger Aperture Example (shallow depth of field, less in focus):

Photo by Elliot Erwitt    © Elliott Erwitt/Magnum Photos

Photo by Elliot Erwitt 

© Elliott Erwitt/Magnum Photos

An example of when you would want to use a Smaller Aperture (E.G. f/8, f/11, f/16) is in bright lighting conditions or when you are taking a picture where you want more in focus like a landscape.

 

Small Aperture Example (wide depth of field, more in focus):

Photo by Josef  Koudelka    © Josef Koudelka/Magnum Photos

Photo by Josef Koudelka

© Josef Koudelka/Magnum Photos


Shutter Speed:

What is a shutter?

Before we tackle what Shutter Speed is, let’s talk about what a shutter is. A Shutter is the mechanism in a camera that opens and closes at set durations to allow a specific amount of light in. It’s usually right in front of the sensor or film.

 

What is Shutter Speed?

Shutter Speed is the duration the image sensor or film is exposed to light. Shutter speeds are represented in fractions of a second. On most cameras with physical shutter speed dials, the speeds are not usually written in fractions. They will read something like “60” or “125” standing for 1/60th and 1/125th of a second. Some more robust cameras will have shutter speed dials with full seconds on the dial as well. Those will usually be written in a different color than the fractions and represent full seconds.

 

Cause and Effect:

As we previously discussed, Aperture affects what is called Depth of Field. Similarly, Shutter Speed affects motion conveyed in still pictures. Slower shutter speeds will keep the film or digital sensor exposed to light longer, so objects that are moving faster than the shutter speed will have motion blur. The opposite is also true. If you use a really fast shutter speed, it will freeze all motion in the frame. This might sound a bit overwhelming right now. We’ll hopefully clear that up with some examples.

 

Shutter Speed Examples:

An example for when you would want to use a Slower Shutter Speed (E.G. 1/30th, 1/15th, 1/8th) is when you want to convey a sense of motion, or the amount of available light does not warrant faster speeds. (Note that slower shutter speeds (1/30th and slower) may be harder to hand-hold and might require a tri-pod)

 

Slow Shutter Speed Example (motion blur):

Photo by Henri Cartier-Bresson   © Henri Cartier-Bresson/Magnum Photos

Photo by Henri Cartier-Bresson

© Henri Cartier-Bresson/Magnum Photos

An example of when you would want to use a Faster Shutter Speed (E.G. 1/125th, 1/250th, 1/500th) is when you want to freeze motion or when the lighting situation is too bright to use a slower shutter speed.

 

Fast Shutter Speed Example (frozen motion):

Photo by A. Abbas   © A. Abbas/Magnum Photos

Photo by A. Abbas

© A. Abbas/Magnum Photos


ISO:

ISO, sometimes referred to as ASA or Film Speed, is how sensitive your camera is to light. The other two variables effect a physical change in how the camera works, like how fast the picture is taken (Shutter Speed), or how much light is let through the lens (Aperture). But ISO is different in that the only thing that changes is how sensitive the camera is to light. ISO is measured in what’s called an ”arithmetic” scale. Which means each time a number doubles, the ISO doubles in sensitivity. Some examples of common ISO sensitivities include 100, 200, and 400, each being twice as sensitive as the last.

 

Cause and effect:

ISO effects something called Grain or Noise (Grain is usually talking about film and noise is usually talking about digital.) The higher the sensitivity to light (higher the ISO), the more grain or noise you will see in the picture. It’s all subjective, but to most, film grain is usually more pleasing to look at, being more uniform and less distracting. Digital noise is usually harsher and has more discoloration. Grain and noise have a similar look to TV static for example.

 

ISo Examples:

Although ISO is one of the three main contributing factors of Exposure, it is generally not used as a creative effect as much as the previous two. ISO is more often used to help the photographer use their desired Aperture and Shutter Speed by either boosting or reducing the camera's sensitivity to light.

An example for when you would want to use a Lower ISO (Less Sensitive to light) (E.G. ISO 100, ISO 200, ISO 400) is when you are in bright lighting conditions.

Low ISO Example (no visible grain/noise):

Photo by Alec Soth   © Alec Soth/Magnum Photos

Photo by Alec Soth

© Alec Soth/Magnum Photos

An example of when you would want to use a Higher ISO (More Sensitive) (E.G. ISO 800, ISO 1600, ISO 3200) is when the lighting conditions may be too dark to shoot in without raising the sensitivity of the film or digital sensor.

High ISO Example (a lot of visible grain):

Photo by Josef  Koudelka    © Josef Koudelka/Magnum Photos

Photo by Josef Koudelka

© Josef Koudelka/Magnum Photos


The exposure triangle, and how to use this information:

At this point in time, you might be experiencing a case of information overload. But I promise this is easier than it may seem. Each of the three attributes of exposure we’ve talked about (Aperture, Shutter Speed, ISO) are all measured in increments that are equal to one another. These increments are called Stops.

What is a Stop?

A Stop is the increment of doubling of halving the amount of light let in during the taking of a picture. Here’s a basic example of how these Stops line up with each other. The stops in this chart are Full Stop Increments, meaning number on the chart doubles or halves the light in the exposure. Some cameras allow 1/2 or 1/3 stop increments which alter the exposure in smaller amounts.