As with all articles on this site, I encourage you to read this a little bit at a time and return to it as often as needed.
Proper exposure is everything. If you cannot take a properly exposed photograph then you cannot take a photograph. It is, I feel, at the end of the day the most important aspect of a learning how to take great photographs.
I feel strongly about this because I see many new photographers try to rush for results and do not dedicate enough time to learning the the basics of how a camera works and how a photograph comes to be. This problem– yes, I view it as a problem! — has become worse as highly advanced, and largely automated cameras have gotten more affordable.
You might ask, “If cameras are automated, then why does it matter?”. To many, it doesn’t. Many people simply want a point & shoot solution and they can get that on even the most advanced digital SLR’s. For the rest of us who want to take more than snap shots, those of us who want to take really great photographs, an understanding of exposure is very important.
One of the reasons that learning exposure as I have laid out is useful is because the settings you change to obtain proper exposure always have two accompanying effects to the appearance of the photograph. I like to call this “the dual effects of settings”. This point is key, so tuck it in the back of your mind for a moment as we’ll return to it several times.
In hopes that I don’t scare you away, I will break exposure down to four simple aspects, all of which you have an impact on (to an extent).
- Available light
- Shutter Speed
Here’s a simple task: Close your eyes for a moment and then open them. When you close your eyes you see nothing. Your eyelids have blocked off the majority of light that enters your eye. When you open your eyes you see what is around you. You see this because there is light in the room. But this light can change in intensity. If you turn the lights off in the room, you can likely still see though the scene looks different. There is less light in the room yet you can still see, and depending on the change in light you can probably see better as time passes. Your body and brain have adjusted to the change in stimuli (learn more about sensory adaptation here). Physically, the iris in your eye has gotten larger so it can take in as much of the light as possible.
This is a simple concept but it is important to realize that your camera works much like your eye in that with a change in the available light you must make a change to your camera in order to still see everything. And much like our eyes, our cameras too have a built in iris. We call this the aperture.
Key Concept: The amount of the light where you are taking a photograph has to be considered. No two scenes are identical.
The aperture is a small iris located in the lens (not in the camera) that opens and closes into bigger or smaller circular openings. The purpose of the aperture is to control the amount of light that is allowed to reach the shutter. A common metaphor for exposure involves a bucket of water with a hole in the bottom. If you think of water as being the light, the hole in the bottom can be thought of as the aperture. If that hole is bigger, more water will pour through it in a given amount of time.
To come back to a camera, the aperture is a hole in the lens that dictates how much light in a given amount of time comes through the lens, through the shutter, and onto your film or digital sensor.
Key Concept: The aperture, located inside each lens, directly controls the amount of light that is allowed to pass through the camera.
The shutter is a mechanical device in you camera that sits just in front of your film/sensor. The shutter opens and closes when you push the shutter release button. When the shutter opens, light passing through the lens is exposed to the film/sensor. The duration that the shutter is open is referred to as shutter speed. This is a very important concept when exposing a photograph.
To refer back to the bucket metaphor for a moment, let’s pretend that the hole in the bucket allows 1 gallon of water per second to flow through. Now, beneath that hole lets assume there is a little flap that opens and closes. If the water is the light, the hole is the aperture, than the flap is our shutter. So with this flap closed, no water is flowing through but as soon as we open it water will flow through at 1 gallon per second because that is what the size of the hole allows for. But the amount of water that passes through that hole is going to ultimately be determined by how long the flap is open. If you only open it for half a second, only ½ of a gallon has passed through your hole.
The shutter in your camera works in exactly the same way. The aperture setting dictates how much light is able to come through your camera in a given amount of time but your shutter is what determines how long that light is allowed to pass through the lens and into the camera and onto your film/sensor. Think of the shutter as the stopwatch of the processes of taking a picture.
Key Concept: The shutter is a timing device that determines how long light is able to pass through the lens and camera onto your film/sensor.
Let’s return to the bucket analogy. Let’s pretend that the water going through the bucket is to serve a specific purpose. For the sake of simplicity, let’s pretend that that purpose is to water a plant. Let us also pretend that this is a very sensitive plant and it requires a very specific amount of water. Too much water and it will drown. To little water and it will dry and die.
If you think of the plant as your film/sensor then you may be able to think of your film/sensor as a “light gathering medium”. And that is all that film or digital sensors are. They are there to capture light. However, like a sensitive plant that requires a specific amount of water in which too little or too much will kill the plant, your photograph lives only with the exact right amount of light.
Different plants require different amounts of water, some are better at utilizing the water you give them. Film and digital sensors work the same way. The ISO refers to the sensitivity of the film or sensor to light. A higher ISO number means that the film or sensor will capture more of the light than a lower setting. In the days of film, this was not something that could be changed without putting new film in the camera. On digital camera’s, this is a setting that you can change manually from shot to shot.
Without getting overly technical we have covered the 4 aspects of every single photograph that has ever been taken. The exposure of a photograph relates to the amount of light that has been captured in the photograph.
There is only a certain amount of available light in any scene. You can add to this light with the use of strobes, lights, or flashes. You can also remove from this light with the use of filters. Often though, the available light of a scene is out of your control. This leaves three specific settings, all of which live on your camera. Aperture, which controls how much light you let in. Shutter speed, which controls how long light is exposed to the film or sensor and lastly, ISO, which is the sensitivity of the film or sensor to that light.
On the surface, this exposure thing seems rather straight forward. For the most part, it truly is. But here is the wild card: Each of those settings effects exposure but each of those settings also effects composure. That is to say, each of these settings impacts how the photograph physically looks. This single concept, from a technical standpoint, is what helps separate snapshots from great photographs.