Jan 14, 2021 | General

Camera Aperture | What Is It and How Do I Use It?



girl with old camera

Want to know what a camera aperture is?  Well, it is the opening in your camera lens that light passes through.  Usually, the size of the opening is variable, but sometimes it is fixed.  Read on for more!

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What is a camera lens aperture?

A camera aperture is, as mentioned above, simply an opening in your lens that allows light to pass through.  You see, the glass on the end of your camera lens is but one part of the lens system itself.  There are many other parts in most lenses that you don’t easily see.

lens aperture small
lens aperture small

One of the parts is the aperture itself.  If you look into a lens that is not connected to a camera, you might be able to see the aperture.  It will look like a series of metal leaves that tend to form a circular opening in the lens.  The leaves can constrict the size of the opening or they can expand the size of the opening.

By changing the size of the opening in the lens, more or less light can be allowed to reach the image sensor in the camera over a given period of time.  For instance, if the scene being photographed is in low light, the aperture can be opened to allow more light in to achieve a properly exposed photograph.

Why does the aperture need to change size?

As we saw above, the aperture can change size to allow more light in for low-light photos.  Conversely, the aperture may need to be decreased if taking a photo in very bright conditions.  As you can see, one of the important roles played by the aperture is to regulate the amount of light that reaches the camera sensor.

Another reason for varying the aperture size is a more creative effect called depth of fieldDepth of field can be defined as the distance between the nearest and furthest objects in a photograph that are in focus.  Put more simply, with a deep depth of field more of the entire scene will be in focus.  With a shallow depth of field, less of the scene will be in focus.

Why would you want part of the scene out of focus?  Well, if you were a crime scene investigator you would not.  You would want all of the scene to be in focus because you would be documenting a scene for future reference.  Keeping the scene in focus and representative of what you would normally see would be important to a crime scene investigator.

sunflower bokeh
sunflower bokeh

For most of the rest of us, having part of the scene out of focus can help draw the viewer’s eye to the subject of the photo.  You might see this a lot with portrait photos with a blurry background, called bokeh.  With the background blurred, the main subject of the photo is in sharp focus and will be what the viewer’s eye is naturally drawn to.  It is aesthetically pleasing and separates the subject from the background.

Aperture isn’t the only factor that contributes to bokeh, focal length, subject distance, and sensor size also play a role in bokeh.  For this discussion, we are simply looking at the contribution the lens aperture plays.

What is an f-stop?

Okay, so we know that the aperture can change size to let in more or less light depending on the scene being photographed.  How do we know how much to enlarge or shrink the aperture to make the photograph come out properly exposed?

While the aperture is adjusted for size, it is not infinitely adjustable.  It has a maximum and a minimum size, as you might expect.  It certainly can’t be larger than the size of the lens!  By the same token, it can’t be completely close or there would be no light at all to take the photo!

Camera lens front with markings
Camera lens front with markings indicating a maximum aperture range of f3.5 to f5.6

Each lens will have a maximum aperture size, which will be marked on the lens somewhere and a minimum aperture that will not usually be listed.  In between those two extremes is where the aperture will operate normally.  The size of the aperture is determined by a number, called an f-stop.  

Infographic explaining depth of field and the corresponding aperture values with their effect on blur and light

Let us talk about the f-stop numbers in the chart above.  As you can see, the aperture openings get larger as you move to the left, while the f-stop numbers get smaller.  Smaller f-stop numbers mean larger aperture openings and vice versa.

A very important thing to note is that each full f-stop change lets in exactly twice as much light or half as much light.  For example, in the chart, moving from f4 to f5.6 lets in exactly half as much light.  Conversely, moving from f4 to f2.8 lets in exactly twice as much light.

As an example, let us say that a particular scene was metered and it was determined that the shutter speed should be one second (shutter open for one second) and the aperture should be set to f4.  That combination would result in a properly exposed photograph.

If the aperture were changed to f5.6 what would we need to do to have a properly exposed photograph?  We know that changing the aperture from f4 to f5.6 lets in half as much light over a given period of time.  Therefore, if we change the shutter speed to two seconds, we would then let in the same amount of light and have a properly exposed image with the new aperture.

This example uses two of the three sides of the exposure triangle, which is another discussion.

What is depth of field?

Depth of field is an effect created by a combination of aperture size, focal length, sensor size, distance to the subject, and distance to the background.  For this discussion, we will work only with the aperture size.

library shallow depth of field
library shallow depth of field

Depth of field, simply put, is the amount of the scene that will be in acceptable focus.  Depth of field is generally measured from the camera forward, so a deep depth of field will be a large area forward of the camera that is in focus.  A shallow depth of field will mean that a short area in front of the camera will be in focus.

sunflower deep depth of field
sunflower deep depth of field

Technically, the depth of field will radiate from the subject that is the focus point.  For any given depth of field, the area in acceptable focus will be divided one-third in front of the point of focus and two-thirds behind the point of focus.

Therefore, however large or shallow your depth of field, one-third will be in front of your focal point and two-thirds will be behind the focal point.

sprinkles shallow depth of field
sprinkles shallow depth of field

Be cautious about using very fast lenses with huge apertures producing paper-thin depths of field.  You can have a depth of field that is so shallow that part of the subject will even be blurred.  This takes some experience and some failures to get used to.  When using a very shallow depth of field for portraits, be sure to focus on the closest eye of your portrait subject.  The eyes are one of the easiest features to notice if they are not sharply focused, so be sure to focus on one of them.


The aperture of your camera is one of the things that you will have to master in order to truly master your camera.  It is one of the most influential settings on your camera both for achieving proper exposures as well as creative reasons.

Using apertures properly, you can draw the viewer’s eye to the subject of the photo, while separating it from the background.  Not only is that a more advanced photographic technique used by professionals, but it is also just more aesthetic and pleasing to the eye.

Understanding apertures and how they work is a big step, perhaps the hardest one, of learning the exposure triangle.  The exposure triangle is fundamental to photography and one of the most important concepts to learn.

If you liked the article, please leave a comment below.  If you would like to see a topic covered here, be sure to leave a suggestion in the link in the menu up top.  Until next time, go take some pictures!



Ralph is an avid photographer in his spare time. He spends a lot of his photography time shooting sports photos of his daughter, who plays softball and swims. He also has a keen interest in mobile photography.


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