What is aperture?
Aperture is the opening of the camera lens, which can be adjusted to control the amount of light that passes through the lens to the image sensor. The aperture mechanism in the lens is formed of a series of opaque “blades” called diaphragm. The diaphragm can be opened or closed to change the size of the aperture.
The size of the aperture is measured by a unit called f-stop or f-number. The f-stop is the ratio of the focal length of the lens to the diameter of the aperture. For example, if a lens has a focal length of 50 mm and an aperture diameter of 25 mm, the f-stop is 50/25 = 2. The f-stop is usually written as f/2 or 1:2.
The f-stop scale is not linear, but logarithmic. This means that each f-stop represents a doubling or halving of the amount of light that enters the lens. For example, f/2 lets in twice as much light as f/2.8, and f/2.8 lets in twice as much light as f/4. The common f-stop values are:
f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22
The lower the f-stop number, the larger the aperture opening and the more light that enters the lens. The higher the f-stop number, the smaller the aperture opening and the less light that enters the lens.
How does aperture affect images?
Aperture has three main effects on your image:
Exposure
Aperture affects the brightness or darkness of your images by controlling how much light reaches the sensor. A larger aperture (lower f-stop) lets in more light and makes the image brighter, while a smaller aperture (higher f-stop) lets in less light and makes the image darker. To achieve a correct exposure, you need to balance the aperture with the shutter speed and ISO settings. Read more about balancing exposure here.
Depth of Field
Aperture affects the sharpness or blurriness of your images by controlling how much of the scene is in focus. Depth of field is the zone of sharpness in front of and behind the subject on which the lens is focused. A larger aperture (lower f-stop) creates a shallow depth of field with only a small area in focus and a blurred background, while a smaller aperture (higher f-stop) creates a deep depth of field with a large area in focus and a sharp background. You can use depth of field to direct attention to your subject or to create different artistic effects. More on this topic in detail below, but first, let’s look at an example:
The images above were taken with apertures on the extreme ends of the spectrum: the one on the left taken at a very small aperture of f/22 and the one on the right taken wide open at f/2.8. Both images were focused on the flower in the foreground. The image on the left (taken at f/22) has a much larger depth of field, meaning that more of the scene is in focus. The image on the right (taken at f/2.8) has a very shallow depth of field, causing most of the scene to not be in focus (other than the flower, which is the focus point). As you can see from this example, aperture can have a drastic effect on the look and feel of your photo. Your choice of aperture for a particular situation will depend on your creative vision and the effect you are trying to achieve.
Diffraction
Aperture affects the quality or clarity of your images by causing light rays to bend or spread as they pass through the lens opening. Diffraction is a phenomenon that reduces the sharpness and contrast of your images when using very small apertures (high f-stops). To avoid diffraction, you can use the optimal aperture for your lens, which is usually around f/8 or f/11. However, performance differs greatly between lenses, so it’s useful to look up reviews and analysis of your lenses to understand under which conditions it performs best. Let’s look at an example of diffraction:
For the particular lens I used for this shot (Canon RF 15-35mm f/2.8), the aperture “sweet spot” for maximum sharpness is around f/5.6. If you look closely at the images above, you can see that the photo taken at f/5.6 is sharper than the one taken at f/22. This is a prime example of a small aperture causing diffraction, leading to a slight reduction in sharpness.
Depth of Field: In Detail
Depth of field is one of the most important concepts in photography, as it can drastically change the creative expression of a photo. As mentioned above, depth of field is the zone of sharpness in front of and behind the subject on which the lens is focused. Depth of field depends on three factors: aperture, focal length, and distance. Let’s look at each one in detail:
Aperture
As we discussed above, aperture is the opening of the lens that controls how much light enters the camera. Aperture also controls how much of the scene is in focus. A larger aperture (lower f-stop) creates a shallow depth of field with only a small area in focus and a blurred background, while a smaller aperture (higher f-stop) creates a deep depth of field with a large area in focus and a sharp background. For example, if you want to take a portrait with a blurred background, you should use a large aperture (such as f/2.8 or f/4). If you want to take a landscape with everything in focus, you should use a small aperture (such as f/11 or f/16).
Focal Length
Focal length is the distance between the lens and the image sensor when the subject is in focus. Focal length also determines how much of the scene you can capture with your lens. Focal length affects depth of field by changing how magnified your subject and background appear. A longer focal length (such as 200 mm) creates a shallow depth of field with more magnification and more blur, while a shorter focal length (such as 35 mm) creates a deep depth of field with less magnification and less blur. For example, if you want to take a close-up of a flower with a blurred background, you could use a longer focal length (such as 100 mm or 200 mm). If you want to take a wide-angle shot of a cityscape with everything in focus, you might want to use a shorter focal length (such as 18 mm or 24 mm).
Distance
Distance is how far away you are from your subject. Distance affects depth of field by changing how much space there is between your subject and the background. A closer distance (such as 1 meter) creates a shallow depth of field with less space and more blur, while a farther distance (such as 10 meters) creates a deep depth of field with more space and less blur. For example, if you want to take a portrait with a blurred background, you should get closer to your subject (such as 2 meters or less). If you want to take a landscape with everything in focus, you should get farther from your subject (such as 5 meters or more).
Below is an example that shows how distance affects depth of field:
The image on the left was taken at an aperture of f/22, while the image on the right was taken at f/2.8. Both images were taken with focus on the center house. Can you spot the differences? In this case, the effects of aperture are quite subtle, but but there are some key differences between the two images:
- First, the tree in the foreground is sharper in the photo taken at f/22 than the one taken at f/2.8. Since I am focusing on a target that is far away, the depth of field is much larger, even at f/2.8. This means that it takes a much larger distance from the focal point for the blurring effect to become noticeable. Most of the scene is in focus for both images, and it’s only the very close tree that starts to exit the depth of field. Compare this to the photos of the flower above, where the difference was much more drastic because the focal point was very close to the camera.
- An even more subtle difference is that the overall image is a bit sharper in the photo taken at f/2.8. This is due to the issue of diffraction that we discussed above. Since the aperture “sweet spot” for this lens is around f/5.6, shooting at an extremely small aperture like f/22 can lead to diffraction issues that cause the overall image to lose a bit of sharpness.