Camera Basics

How does a camera work?

A camera works by taking light, bending it through a series of lenses, passing it through an aperture and onto a sensor. In a film camera the " sensor" is light sensitive film, and in a digital camera, A sensor that converts red, green and blue light into pixels is used. For our purposes everything below will assume a digital camera.

when a photo is taken, a "shutter" is opened, allowing for light to pass through the camera onto the sensor for a short amount of time, and then the shutter is closed.

the more light that hits the sensor, the brighter the image. The amount of light hitting the sensor can be controlled by three variables; Aperture, ISO and shutter speed.


exposure is the method by which the "brightness" of a photo gauged. When we say a photo is overexposed, that means that too much light is hitting the sensor, and it just registers as white. When we say underexposed, it means not enough light is hitting the sensor, and some parts of it register as black.

Above we can see examples of this. On the right of the photo are their histograms, which show a distribution of how many light and dark pixels there are in the photo. So the left of the graph is black, and the right is white. The correctly exposed photo shows how a very small part of the image is at the extremes of the graph, either light or dark. The overexposed and underexposed photo's histograms show how the distribution is pushed to the extremes of the graph, with a large portion of the image being either only white or black.

Exposure is controlled by 3 factors, ISO, shutter and aperture. If your exposure is not right, an alteration to any one of those factors could correct it. The relationship between the three can also be leveraged for your advantage, but we will go into that a little later.


ISO is a measure of how sensitive the sensor is. Derived from film sensitivity/speed, the higher the ISO number, the more sensitive the sensor. The downside to increasing ISO is that although sensitivity goes up, so does noise.

These comparisons have different shutter speeds for each ISO level to keep the photos exposures the same.

In general increasing ISO will increase exposure, as seen below

Shutter speed

Shutter speed is perhaps the simplest methods of controlling how much light hits the sensor. When you take a photo, the shutter, a device in the camera that either blocks or lets light through, is opened for a set amount of time, after which it closes again. For example a shutter speed of 1/60 means that light will be let onto the sensor for a total of 160th of a second. If we wanted to allow more light onto the sensor, and increase the exposure of our photo, we could set it to 1/30.


the aperture is a diaphragm within the lens, that widens and narrows depending on what it is set at. f/1.4 is considered a wide aperture, of fast, and something like f/16 or f/22 is considered a narrow or slow aperture. naturally the wider the aperture, the more light can hit the sensor, the brighter the exposure. It is a simple way of changing exposure while not affecting ISO and shutter speed.

However, changing the aperture changes characteristics in addition to exposure. Most notably, depth of field. Due to the physics of lenses, the wider the aperture, the less things will be in focus, also known as a narrower depth of field.

Continue onto Still Photography basics to see more information to help you take good photos.

Using the camera

Swapping lenses

Memory cards


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