In the last lesson we learned that “aperture” controls the amount of light that reaches the camera sensor, by changing the size of the hole in the lens.
As we change the size of the hole in the lens, not only does it change the amount of light but also has an effect on how much of the image is in focus, called “Depth of Field” (DoF).
We can see from the image of the girl on the left that while her face and body are in focus, the trees in the background are completely out of focus. This is the “creative” control that the “aperture” setting provides, which is the ability to control how much of the image is within acceptable focus. Looking at the ground behind the girl’s foot we see the point where the ground goes from being in focus to blurry and then increasingly blurry the further we look toward the trees in the background.
Looking at the lighthouse image on the left, we can see with an aperture setting of f/16, all of the image from the puddle reflection through to the lighthouse and then to the sky including the sun are all in focus. By setting our camera to a smaller aperture we can maximize the depth of field.
To summarize, “Depth of Field“, (DoF) is defined as the area of an image that is within acceptable sharpness, in front of and behind the focus point. The larger the aperture, for example f/4 (the image of the girl), the less DoF. Conversely the smaller the aperture, for example f/16 (the image of the lighthouse), the more DoF in an image.
In the next lesson we will learn how to change the aperture setting on your camera.