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What is an Aperture on a Lens and How to Use it

There are a variety of different elements that go into composing a beautifully framed shot. Whether you’re using a Canon or Nikon, RED or Arri, there are some camera settings that remain consistent throughout the marketplace. Aperture is one of them. Previously referenced in our Exposure Triangle article, we will take a deeper dive into what exactly aperture is, how different cameras are affected by a lens’s aperture capabilities, and how you can best utilize it for your productions.

Understanding Aperture

Aperture has multiple names affiliated with the process of adjusting aperture, and people tend to refer to it with any one of these names at random. This is why it is important for you to get familiar with the multiple ways photographers and filmmakers talk about aperture, and to understand why they use those names. The most popular words we use in the media world are: aperture, iris, diaphragm, and f-stop. These all represent overlapping elements of the lens adjustment process, but let’s dive a little deeper into what each of them means.

The Elements of Aperture

Aperture is the most common name and one that encompasses all the others. Perhaps it is the most frequently used because it resembles what it signifies in the physical world. The lens aperture is the opening on the lens through which light passes and hits the camera’s sensor or exposed film. The aperture on a camera lens is adjustable, allowing for multiple different aperture possibilities within the same lens. A larger aperture allows for more light to enter through the lens, which adjusts the focus abilities creating a shallow depth of field in the image, generating what is known as bokeh, or a specific form of blurred background, in the out of focus background of your focused subject. Large aperture allowing in a lot of light makes this setting great for low light scenarios such as around sunset or, depending on the camera’s capabilities, night shooting. Shooting wide open, with a low aperture value, is a great way for film and digital cameras, such as a DSLR camera, to capture scenes you otherwise couldn’t without the assistance of artificial light. However, not all lighting conditions require as much light, leading to the best aperture for the correct exposure not requiring a wide aperture, but rather the size of the aperture should be minimized. This would be called a narrow aperture, or a smaller aperture. Having a small aperture allows you to successfully shoot in higher lighting conditions, such as daylight or under bright studio lights. Having a lens opening with minimum aperture will create a deep depth of field, causing very little difference in sharpness between a subject in the foreground and the background.


Believe it or not, us humans have an aperture setting built in our bodies. The only difference between us and the lenses we use is that we can’t control it manually based on a given circumstance, but it’s our bodies that control our “aperture” based on the level of light occurring within the environment we currently inhabit. In a similar way, the lenses we use have an “iris” that looks very similar to the iris in our eyes, which is where the camera element derived its name. Inside each lens, there are blades that can be adjusted to open or close depending on if more or less light is necessary to pass through and hit the sensor of your camera. The irises in our eyes relax with low light (making our pupils appear larger and let more light pass through), and they shrink or contract in bright light environments (thus shrinking our pupils and letting less light through, so we can see). Here’s a picture that illustrates this.


Diaphragm also alludes to our human bodies. While they are not exactly the same, they do share some similarities. The aperture is the actual opening through which light passes, while the diaphragm refers to the blades that open and close to control the size of that opening. The widest aperture is achieved when the blades are pulled as close to the interior walls of the lens as possible. As an inherent design limitation of camera aperture, the aperture range is limited by the amount which the diaphragm can be retracted and extended. No diaphragm is capable of being pulled fully to the side of the lens interior wall, but some can get fairly close.


This is the most technical way in which photographers and filmmakers refer to the aperture, and it is the scale we use to measure the amount of light passing through the lens. Lenses have different f-stops, measured by different f-numbers. The best ones have a wider aperture, up to an f-stop number of f/1.2 or even f/0.9, while cheaper, more affordable lenses tend to have maximum apertures of f/4 or f/5.6. Additionally, the type of lens has an effect on maximum aperture. Zoom lenses usually have a minimum aperture number higher than prime lenses due to the nature of their construction. If you’re confused, don’t worry. More on this later.


Now that we know what we’re talking about, let’s discuss why aperture is so important to understand and master when it comes to filmmaking. Aperture is one of the three ways in which we can control our exposure in our camera (the other two being shutter speed/angle and ISO). That means that controlling our aperture will allow either more or less light to come through the lens and into our sensor, thus affecting how bright or dark our image looks.

But, this is not the only thing that aperture does. Have you seen those beautiful images where the subject (whether it’s a person, an animal, or an object) is in focus, very sharp, and the rest of the background is blurry? Well, that’s how our photo or video gets affected when we manipulate the aperture on our lenses. The lower the number in the aperture (f-stop), the wider the aperture. That means that an aperture of f/2.8 will be wider, and consequently will allow more light through that an aperture of f/5.6. On the other hand, aperture affects depth of field directly. That means that changing our aperture will also change the range of distance in which our subject will be in focus. If our f/stop is very low, like f/2.8, our subject will be in focus but the rest of the image (foreground and background) won’t. On the contrary, if we have an aperture of f/11, both our subject and the background will be in focus. You can read more about f-stops here.

F-stop vs T-stop

You’re right, it’s a bit confusing. If you ever see people talking about T-stops rather than f-stops, don’t panic. Usually photography gear will use f-stops, while professional cinema gear will list t-stops. That doesn’t mean consumer photography gear doesn’t have t-tops or vice versa. There is one main difference between these two and that is that while an f-stop measures the size of the opening at the front of the lens, a t-stop measures how much light, having passed through the aperture and through the elements in the lens, actually gets to your sensor.

This means that some light is lost in the process of it getting to your sensor, and it’s due to the fact that lenses have multiple glass elements inside them that reflect and deflect light, and in the process of passing through all those glass components, some light is lost and less light makes it to your sensor. You can watch this video that explains this in much more detail.


All in all, aperture is a major thing to know and understand inside out, because it will directly affect every photo or video you take with your camera. Knowing these tools will help you be intentional with your work, rather than letting the automatic setting on your camera choose for you. Controlling the aperture allows you to both let more light into the camera, and control the depth of field in your shot (range of distance in which a subject will be in focus).


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