What is aperture?

Susan Fernandez November 11 2021

Do you know what is an aperture is in photography? And what effects it has on our photos? No worries if you don't, because after reading this guide you will know everything about it. And hopefully, it will help you to notch your photography skills up by an entire level. Let's get started.

There are three central pillars of the camera: ISO, Shutter Speed, and lastly, aperture. Complex terms like depth of field and f-stops might seem overwhelming to beginners but trust me; they are pretty easy to understand.

What Is an Aperture

The literal meaning of aperture by the dictionary is a hole, gap, or opening. You know light plays an essential role in taking a picture, and a lens aperture is that opening through which light enters the camera.

You can control the amount of light entering the camera lens by opening or closing the aperture. It works almost similar to the human eye, like when there is more light the pupil shrinks, and when it's dark, the pupil dilates.

The 2 main elements that aperture controls are

  • The brightness and darkness of the image (Exposure)
  • Determines the level of focus in the image (Depth of field)

What Does Aperture Control in Photography

Exposure (Light)

The concept of the aperture is straightforward. If you want a bright photo, you will have to open the aperture more and if you want a dark image, keep the aperture small. This control over light sometimes allows you to take creative shots. But there are times when you have to adjust the aperture according to the light available to the camera.

Professionals talk about aperture in terms of f-stops or f-numbers. For example, you might have heard professional photographers talking about aperture, like" what aperture are you working at?" and the answer might be an "f" followed by a number (e.g., f-10).

You have to learn these f-stops by heart in photography schools, but it's not something set in stone. In fact, most people don't remember them. They keep a general rule in mind that the larger the number, the smaller the aperture, and the smaller the number, the larger the aperture. 

If you find this confusing, then remember it in this way that the closer the number following the "f" to zero, the brighter the image. And the closer it is to one, the darker. If you want a bright image in Aperture priority mode, then set a low f-number and the camera will automatically select a larger aperture. 

For instance, if you are at f-3.5, which is considered a very small aperture for taking photos but don't want to increase ISO or decrease the shutter speed to get more light into the camera, you can either increase your f-stop by moving towards smaller numbers or decrease your focal length (zoom) of the lens to achieve more light.

Similarly, if you want a dark image in this mode then use a higher f-number with a wider aperture i.e., move towards larges numbers after the "f". A common trick used by professionals to keep the aperture constant is that they use a tripod and then move towards or away from it.

Depth of Field (What's in Focus)

Besides controlling the amount of light entering the camera lens, the aperture has another duty to adjust the focus. You might have seen images where some things in a photo look very sharp and focused while other things are blurry and out of focus.

The word bokeh is used to mention the blurry part of an image. It is a Japanese word that means blurry or hazy. Professional photographers use the word DOF (depth of field) to talk about blurry and sharp objects in a photo.

We can simplify it even more by naming it as a "focused area." If you hear a photographer saying that this image has a shallow or small focused area, it means that only a tiny part of the image is in sharp focus, and most of the image is blurry.

Similarly, if an image has a large or deep focused area, it shows that most of the image is in focus, and only a tiny or no part is blurry. There is another rule to remember if you want to control the focused and blurry effect. Bigger the aperture, the smaller the focused area (DOP). If you want to work with the large focused area, then use a small aperture size (large f-numbers) and if you want to work with the small focused area, use a larger aperture (smaller f-numbers).

So bigger opening in the lens means a smaller focused part in the image and a more out-of-focus area.  The smaller the aperture, the larger is the focused area in an image and less blurry.

Background Control in Photography (What's Behind)

Aperture is not only for controlling light & focus, but also background blur or "bokeh." If you want to take a portrait of someone and you want to make them stand out from their surroundings, then you either use flash photography or do it without flash by using a large aperture that controls both light and bokeh. This way you can keep your subject in focus while blurring out the background around him/her.

It's not possible to get this type of effect if we use small aperture settings because we will need more light and longer shutter speed which means we won't be able to handhold the camera without getting a blurry image due to camera shake.

A larger f-number means larger blurred background which is great for portraits or any kind of product photography because you can keep your subject in focus and make the background blurrier.

Similarly, if we use smaller aperture settings, then our picture may have a narrowly focused area where only a small part would be in focus while the rest will appear out of focus or blurred. If you take a portrait with a person standing in front of a beach then all objects that are behind that person's body will be more out-of-focus than that person, making him/her stand out from their surroundings.

There are situations when you either want an extremely large bokeh effect (small f-number) or you want an extremely shallow focused area (big f-number). If we use small aperture settings, then our final image would have a bokeh effect with less background blur.

When you want to take a photo of a city from somewhere high up and you just want the prominent buildings to be in focus while the rest is blurry then this effect can't be achieved by using smaller aperture settings because there won't be enough light. In that scenario, you'll need larger f-numbers so that your camera can collect more light and it will also help with controlling "bokeh" effects.

Similarly, if we need a deep DOF or a large amount of blurred background, then we should use larger f-numbers. The trick is to change the aperture while keeping everything else constant and that way we can control light intensity, bokeh effect, and DOF according to our needs.

When to use aperture priority mode?

That's the most common question by beginners. They know how to adjust aperture according to their needs but they don't know when it is necessary to use that mode.

When you are shooting indoors where there is not very much light, then an automatic mode will fail you because your camera will start increasing your sensitivity (ISO) in order to capture enough light for a good picture and this will result in noisy images.

So if you want photos with nice colors and noise-free images then switch your camera to Av or Aperture priority mode so that your camera won't change ISO on its own accord. You can still leave ISO at its default or lowest value if you feel confident about manually controlling shutter speed and focusing precisely on the subject of the image.

Some photographers like to do street photography and other candid work where they don't want their subjects to notice that they are being photographed. In such cases, you can switch your camera to Av/Aperture priority mode so that your camera won't make a sound while taking photos and will let you take the photo at any time without waiting for focus to lock or waiting for slow shutter speed, ISO and aperture adjustments.

Of course, this depends on how good the autofocus of the camera is but even if your camera doesn't have very fast autofocus then it should still be able to capture sharp images quickly enough before people get out of frame. You just need to turn off auto-everything (autofocus, auto-ISO adjustment) and you should be fine.

Will your photo be brighter or darker when changing the aperture?

When you change the aperture, your shutter speed and ISO settings won't be affected. Only depth of field will increase or decrease (hence a bit of background blur) but the overall brightness of the scene is not going to change because it's controlled by shutter speed.

With small f-numbers light intensity decreases but the shutter remains open for the same amount of time to capture more light; with large f-numbers, the shutter stays open for less time so there will be less light in your image.

What does each stop mean?

Each stop means that either your aperture size increased or decreased by "1". This is one way how photographers describe different aperture sizes which are actually fractions written in decimal form like 1/2, 1/5, etc.

So f/1.4 is a larger aperture than f/2, which in turn is larger than f/11 (11th stop).


Aperture is responsible for controlling the depth of field and the amount of background blur in your images.

Smaller f-numbers mean larger apertures with less DOF; which is useful when we want to focus on the main subject and don't want any distracting background details (like dof effect) or if we need deep DOF because the scene we are photographing doesn't have much light available.

Now you understand the importance of aperture - it’s time to put the new knowledge into practice!