Creating an exposure
When you take a photograph, your camera is choosing three variables. Together, these variables make up the exposure, or the amount of light that is recorded by the camera.
The three variables are shutter speed, aperture, and ISO.
- Shutter speed is how long the shutter remains open - imagine you are opening a tap to fill a glass of water. If you open the tap for a long time, you get a lot of water, while if you open it only briefly, you only get a splash.
- Aperture is the size of the hole the light passes through inside your lens. A small aperture means that less light reaches the imaging sensor. A large aperture means you’ll get a lot of light.
- The final variable for exposures is ISO. This doesn’t directly affect the amount of light that goes into the camera. Instead, it sets the sensitivity of the imaging sensor.
Scenario 1: If you accidentally overexpose your photos, you will lose a lot of the detail in the highlights. You can reduce the exposure by using a faster shutter speed, a smaller aperture, or a lower ISO value.
Scenario 2: If you underexpose your photo, it's tough to get right details from dark areas. You can increase the exposure by using a slower shutter speed, a larger aperture, or a higher ISO value.
Shutter Speed is the game of movement. What shutter speed is correct for the exposure? Any shutter speed can be “right” depending on the effect you’re aiming for - whether it is to freeze motion, imply motion, blur motion, or simply take a photo of a scene. It also depends on whether the subject or movement is moving toward or away from you, from one side to the other, or not at all.
Shutter speed is measured in seconds, or fractions of seconds. The length of available exposure depends on your camera’s settings, and can typically range anywhere from 30 seconds (really slow) to 1/8000 of a second (really fast). The amount of light let in through the shutter is directly proportionate to the amount of time the shutter is opened - so an exposure of 1/500 of a second lets in twice as much light as 1/1000 of a second, and so on.
The aperture is the variably sized hole in your camera’s lens that controls the amount of light that is allowed through it to hit the sensor. A larger aperture enables more light to hit the sensor for the duration of time the shutter is open. Aperture is an important element for getting the correct exposure, but also adds a new twist to your photographs: depth of field. Aperture is expressed in ƒ/stops (ƒ/1.8, ƒ/5.6, etc.) In order to be confusing, a smaller ƒ/stop number indicates a large aperture.
So why not let in the most light possible on every shot? The key to using aperture is to understand that different apertures will affect the shot’s depth of field - the amount of sharpness in front of and behind the plane of focus (the sharpest part of the photo).
ISO is a measurement of your camera sensor’s sensitivity to light. The higher your camera’s maximum ISO number, the more sensitive it is to light, meaning it (theoretically) should be able to perform better in low-light conditions. Every time you double the ISO number, you double the sensor’s sensitivity to light.
When you look at something that is white, or gray, or any other color, your eye sees the light and your brain interprets the colors.
When the light changes (say from daylight to interior light, for example), your eyes automatically adjust so the colors appear the same, even though they are not. Unfortunately, a camera sensor does not have the same luxury, which is why it uses white balance to ensure that each shot captures the right color temperature. Sadly, whilst your camera is pretty good at estimating white balance, it occasionally gets things wrong - so let’s take a look at how light works, and what affects white balance in your images. All light has a different color - ranging from blues and greens to reds and oranges.
Understanding the different colors of light can help you as a photographer to recognize when white-balance adjustments are needed in order to render your shot in the right color, or to adjust the color of the shot to get a better photograph.