Aperture refers to the amount of light which come through the lens of a camera to strike the image sensor. There is an iris within the lenses of DSLR cameras, which is often opened and closed to put the limitation on the light amount that reaches the image sensor. The f-stops is the measurement of the aperture. The aperture of a DSLR camera brings you the two features: the light amount coming through the camera lens and the level of depth of field.
The Range of F-Stops
There is a wide variety of F-stop numbers, especially on the lenses of DSLRs. However, the maximum and minimum number of f-stops shall base on the camera lens quality. The image quality can be lower when the aperture is small (you will understand this term in my explanations later in the article) and based on the design and quality, the minimum level of aperture is limited in some lenses. The common lens range is from f3.5 to f22, but the range of f-stops in a variety of lens can be: f1.2, f1.4, f1.8, f2, f2.8, f3.5, f4, f4.5, f5.6, f6.3, f8, f9, f11, f13, f16, f22, f32, f45.
Usually DSLR cameras has a larger number of f-stops than film models.
Aperture and Depth of Field
First, let’s start with the most basic feature of the aperture: the capability to control the camera depth of field.
Depth of field (DOF) refers to level of your photo in focus around the subject, which means that the targeted subject will be sharp and the foreground as well as the background becomes blurry when the depth of field is small. The higher the DOF is, the less focused the main subject is, so the entire photos will be sharp throughout the depth.
A small DOF will be useful for shooting some certain kinds of subjects, for example jewelry or creatures and a large DOF will be more proper for shooting photos on landscapes. There is no rule for setting the right DOF, as it just depends on your own purpose of shooting certain subjects.
To understand the f-stops, just keep in mind that a small DOF is shown by a small number. For instance, f1.4 refers to a small number and the DOF will be small. Meanwhile, the large number is to show a large DOF. For instance, f22 is an example for this case and the DOF will be large.
Aperture and Exposure
Photographers are often confused about this.
When the aperture is small, the relevant f-stop is represented by a higher number. Therefore, f22 refers to a small aperture while f1.4 refers to a large one. Photographers often easily get confused because the whole mechanism seems to be back to front! Just keep in mind that with the f1.4, you will have the iris of the lenses widely opened that allow a huge amount of light to come into the image sensor, so this aperture is large.
In addition, there is another way to remember the relation of f-stops and the aperture. In fact, the aperture refers to an equation in which the aperture diameter divides the focal length of the lens. For instance, your lens has the measurement of 50mm and you have the widely opened iris, there is likely a hole with the diameter measurement of 25mm. Therefore, the result is 2 when you have 50mm divided by 25mm. In this case, the f-stop is f2. If you have the smaller aperture (3mm, for instance), the f-stop will be f16 when 50mm is divided by 3.
Adjusting the aperture setting is known as “stopping down” (if the aperture is set smaller) or “opening up” (when the aperture is set higher).
Aperture’s Relationship to Shutter Speed and ISO
Because one of the functions of the aperture is to control how much light will pass through the camera lens to hit the image sensor, the photo exposure will be affected by the aperture setting. Meanwhile, the Shutter speed refers to the duration that the camera opens the shutter button, which also affects the exposure.
Consequently, in addition to determining the DOF through the aperture configuration, you should also pay attention to the amount of light that come through the camera lens. If you need a small DOF and select the f2.8 number, for instance, you will also need to increase the shutter speed to a pretty fast level to make sure that the camera does not open the shutter for long, which results in overexposed images. A slow number of shutter speed (for example, 1/1000) enables you to shoot very fast moving subjects while a high number of shutter speed (for example, 30 seconds) will be suitable for shooting photos in low light, such as in the night time. You should decide the exposure based on how much light is currently available. If you are primarily concerned about the DOF, the shutter speed shall be adjusted accordingly.
The ISO setting also has the relation with the aperture setting as it brings more light when needed. A higher number of the ISO (found with a higher number) will be very useful for shooting under low light conditions while you don’t have to change the shutter speed or aperture. However, don’t forget that your images may have more noise when the ISO is higher and you may easily encounter photo deterioration. To understand that, the ISO should be considered as the final way.