Exposure is the most fundamental concept to wrap your head around in photography. Each photograph is an individual exposure (excluding double exposures) comprised of three components: aperture, iso and shutter speed.
Cameras nowadays have very accurate inbuilt metering systems. We can actually let the camera do a lot of calculation for us. But, this doesn’t mean you can stop reading now. A fundamental understanding of the components that go into each exposure is essential.
This understanding will allow you to push the camera to its limits. From here you can explore areas of photography that seemed impossible to you before. Next time you take your camera out you will be able to predict the outcome, before you shoot.
This article will teach you the following:
- What components make up an exposure?
- How do each of the components interact?
- How to modify a shot to get a correct exposure.
What components make up an exposure?
- Shutter Speed
Aperture is the size of the lens' diaphragm. This controls both the amount of light that comes through onto the sensor and the depth of field. The aperture is indicated by the letter f and followed by a number e.g. f2.8, f4, f5.6, f8, etc.
The Shutter Speed is the length of time that the shutter remains open. This allows more or less light onto the sensor (or film). Shutter speed is denoted in fractions of a second (1/500s, 1/250s, 1/5s, 2s, etc).
ISO determines the sensitivity of the image sensor (or film) to light. This is is denoted by an ISO number, typically ranging from 100 - 6400. The higher the number the more sensitive the sensor is to light
All three of these components combine to give an exposure (EV). A change to any of these settings will have an effect on the exposure. Maintaining a balance of Aperture, Shutter Speed and ISO is how cameras take photos. But cameras don't know the exact shot you have in mind. To let's take control.
How do each of the components interact?
All three values are independent of each other. The common denominator of each of them is light. The more light that is captured the more "exposed" the image is. Too little light, the image is underexposed. Too much light, the image is over exposed. See below:
A smaller aperture will result in much less light being allowed onto the sensor than a larger aperture. Aperture values are numbered with the lowest being wide open and the highest, closed right down. See below:
Each aperture step in the above graphic indicates one stop of light that is allowed onto the sensor. Opening up by one f-stop will increase the amount of light onto the sensor by one stop. Closing down by one f-stop will decreasee the amount of light onto the sensor by one stop.
Each shutter speed step in the above graphic indicates one more (or less) stop of light. A fast shutter speed allows a lot less light onto the sensor than a slow shutter speed. Unlike aperture numbers shutter speeds are denoted as you would imagine. Each number represents the exact time that the shutter will remain open
ISO is a little different than the other values. For years ISO was fixed when you loaded the film into your camera. You had ISO 100 film or ISO 400 film etc. Nowadays digital cameras can ramp up or down the sensitivity of the sensor to provide a correctly exposed image.
A higher ISO will make the sensor much more sensitive to light. Therefore it takes less light to make a correct exposure. This is good for night photography, very fast shutter speeds or a narrow aperture. However high ISO comes at a cost. The higher the ISO the more noise is introduced into the image. See below:
Tip: Don't be afraid to crank the ISO up in low light. Noise can be removed in post processing. Motion blur or an unfocused image cannot be fixed in post. Just slide up the luminance slider in Lightroom. Values between 20-30 will remove a lot of the noise without runining the picture.
The best way to think about exposure it to imagine a triangle. If we start off with a perfect exposure then open up the aperture by one stop. We would need to lower either the ISO or the Shutter Speed. If we were to want a faster shutter speed then we would need to either open up the aperture or raise the ISO.
Let us start by winding each of the dials on my camera and creating a random exposure. Set your camera to (M)anual mode and set any ISO, Aperture and Shutter speed that you like. Here was my output (ISO100, f8 at 1/500s):
At this stage your image may be overexposed or underexposed. As you can see my image is rather underexposed (black). We will use this as the starting point.
Now we know how each of the components interact we can start to look at how we can improve the exposure. It was too underexposed. It is now that we must think what we are trying to achieve in the photo, is the subject moving? Do we want a deep or shallow depth of field? What are the lighting conditions?
What do we know?
We need to raise the exposure. The subject is stationary. A medium depth of field is required.
Tip: Before we continue go into your camera and turn on overexposure warnings. We are able now able to see where we have overexposed the image. Areas of underexposure can be recovered. Very overexposed areas cannot be fixed and will result in an area of white that has no data.
We will use the camera's inbuilt meter in order to gain an understanding of where we are with exposure. Half push the shutter button and look at where the arrow falls on your meter.
Here we see that the meter is indicating that we are underexposed by 2 stope (follow the yellow arrow). So we can raise the the aperture, shutter speed or ISO up by two stops to achieve the correct exposure.
Start by thinking about depth of field. For this image we will maintain a medium depth of field with an f-stop of about 5.6. Because the subject is stationary we can make creative decisions here.
As the subject is stationary we can lower the shutter speed which to let more light in. But lowering it too far will require us to use a tripod. The rule for hand holding is "1/focal length". So a 35mm lens should have a minimum 1/35s shutter speed, a 200mm lens 1/200s etc. Below that we will have too much motion from our hands to get a decent shot.
Next step is to raise the ISO in order to produce a correct exposure. Here we raised the ISO to 6400 before the meterindicated that we have a correct exposure.
Tip: To easily work in manual mode set the Auto ISO limits in your camera between 100-6400. If your camera is older and doesn't perform well at 6400 then drop the upper limit to 3200. Then you can focus on Aperture and Shutter Speed and let the camera fix the ISO to create a well exposed image.
The best way to get better at this is to practice. It doesn't take long to get an understanding of how the camera works. Soon you will realise start thinking about what settings would be optimal as you move through life. A shady area will require a higher ISO, or a slower shutter speed, or a wide open aperture. As you move into the sun you will think about how things will need to change.
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Ben Kepka - The Cultured Kiwi