Aperture, What It Is and How to Use It Creatively

F stop, depth of field, bokeh, opening up, stopping down, what do these words have in common? These are all terms that relate to your camera’s aperture. In this article, we’ll look at the technical side of aperture, then explore how to use aperture for creating interesting and unique photographs.

Goals

• Learn what aperture is and how it works (take it apart)
• Learn how to use aperture creatively in your photography

What is aperture

When we talk about aperture there are a variety of words/phrases used that can be confusing. In order to make things a little easier let’s start with a quick rundown of the terms you’re likely to hear and start using.

Terminology

• Aperture – the ratio of focal length to the diameter of the opening that allows light to reach the negative or image sensor.
• Stop – a stop (of light) is either a doubling or halving the amount of light reaching the negative or image sensor.
• F-stop – the measuring system for aperture, expressed f/1, f/1.4, f/2, etc.
• Stop down – make the aperture smaller (let in less light)
• Open up – make the aperture larger (let in more light)
• Depth of field – how much of the scene is in focus
• Lens – fast/slow – a reference to the maximum aperture of the lens (today a “fast” lens would have a max aperture of f/2.8 or larger)
• Lens – constant/variable aperture – does the lens allow the same aperture throughout its zoom or not. For example, a 70-200mm f/4 is a constant aperture lens. A 28-135mm f/3.5-5.6 is a variable aperture lens. ***Note this applies only to zoom lenses, not prime.

Aperture, what it is and how it works

Now that the boring stuff is out of the way, let’s roll up our sleeves and learn how aperture works.

As I said in the terminology section above, the aperture is the ratio of the focal length to the diameter of the lens opening. It is expressed, mathematically, as N=f/D. “N” = aperture. “f” = focal length. “D” = diameter of the lens opening.

In other words, aperture is a way to express the size of the opening in your camera’s lens through which the light enters. The size of the opening is denoted by a value called the f-stop. This is where things tend to get a bit tricky for a novice photographer.

A good way to think about aperture is to consider how your eyes work. When you step outside on a nice sunny day your pupils contract to a very small diameter to keep you from experiencing pain and because you don’t need any more light to see the world around you. Conversely, when you enter a dark room, your pupils dilate to let in more light.

You use the aperture on your camera for the same reasons. Either to let more or less light reach your negative or image sensor. However, to use it effectively it helps to understand how this works.

If the purpose of the aperture is to control the size of the opening that lets light into the camera, how do we know where we start and how much change we are making?

Stops and f-stops

When we talk about the amount of light in photography, we rely on measuring light in stops. A stop is either doubling or halving the amount of light for a scene. While understanding stops is important, it is not the end of our discussion. The next step is to measure the changes you are making. 

Changes to aperture are measured by a term called the f-stop. The standard values for f-stop range from f/1.4 – f/22. Some specialized lenses offer larger and smaller apertures.

Time for a quick test – between f2.0 and f16.0, which opening is larger?

If you said f16.0, you’ll be surprised to know that the f2.0 aperture is actually larger diameter. This is due to the fact that the f-stops; 2.0, 4.0, 5.6… are actually calculated as 1/2.0, 1/4.0, 1/5.6… Photographers have just developed a shorthand method of talking about aperture and f-stop that omits the fraction. Let’s take a look at the following table for visualizing aperture and f-stops.

What strikes you about this chart? Do you see how much smaller the opening is at f/16 than f/2? What impact do you think that has on the amount of light striking your film or image sensor?

As you can imagine, the smaller the opening the less the amount of light that enters the camera. Think of this as your own pupil. When you are in a dark room your pupil dilates (gets bigger), but when you step into the sunshine your pupils constrict (get smaller). 

The lens aperture is meant to mimic the behavior of the eye. In a dark room, you might “open up” your aperture from f8.0 to f4.0 or less. On a sunny day, you might “stop down” your aperture from f4.0 to f8.0 or more. 

One final thing to note about this chart is that it shows full stops between different f-stop values. 

Stopping down and opening-up

I know we touched on this in the beginning but the terminology is important. If you find yourself talking with another photographer, watching a “how-to” video online, or reading other articles you are likely to encounter the phrases “stop down” or “open up”. Stop down means reduce your aperture. Open up means increase your aperture.

What else does aperture control?

In addition to controlling the size of the opening/amount of light entering the camera, aperture also controls the depth of field for your image.

Depth of field – the portion of your image that is in focus

Take a look at the following figures to visualize the concept of depth of field.

In the first image, the scene is in focus from the subject to the tree in the background. This is a large depth of field. Commonly, this is what you would expect to see in landscape photography. 

In the second image, the focus of the scene drops quickly behind the subject. This is an example of a shallow depth of field. You see this a lot in portrait and macro photography. Think “portrait mode” on your iPhone. Shallow depth of field helps draw attention to the subject while removing distractions in the background.

How does aperture determine the depth of field

Photography is an art of balance. For every setting you change there is another calculation you must consider.

In general, the larger the aperture, the shallower the depth of field. By contrast, the smaller the aperture, the greater the depth of field (to a point). Every lens has a range of apertures that yield the sharpest images. So, if you’re photographing a landscape on a sunny day don’t just stop down to f/22 and expect tack-sharp focus. There are other factors to consider, but that is for another time.

Depth of field in practice

Diagrams are nice, but practice is better. I set up three characters, 20 inches separate the first and second characters, and 20 inches between the second and third characters. The purpose of this experiment is to demonstrate the correlation between aperture and depth of field.

In the series of six images the f-stop ranges from f/4 in the top left to f/22 in the bottom right. The series of aperture is as follows: f/4, f/5.6, f/8, f/11, f/16, & f/22. Do you notice how the background becomes clearer with each stop?

For a clearer comparison, take a look at the following figure. As you move the slider you can control the depth of field between f/4 & f/22. While the background is not perfectly sharp, you can make out significantly more details in the f/22 image versus the f/4.

Recap of technical topics

• Aperture controls the amount of light coming into the camera by controlling the diameter of the lens opening
• Measured in f-stops
• Aperture controls the depth of field of your image

Getting creative with aperture

Now that we’ve finished discussing the technical aspects of aperture, it’s time to get to the fun part. Let’s talk about how to use aperture creatively.

For the creative section, I thought I’d talk through some examples.

Bokeh – sweet, sweet bokeh –

This term refers to a very shallow depth of field. You’ll find this used in portrait photography. The characteristic look is a soft, out of focus background with a strong subject in the foreground. Portrait photos that have this effect are shot in apertures of f/1.8 or greater. 

Note: Be sure to focus on your subject’s eyes and make sure that his/her nose is also in focus. When you are working with such a shallow depth of field the nose can be out of focus.

Macro photography

Along with bokeh, macro photography makes use of wide apertures to create shallow depths of field for subjects. Usually, macro photographers employ specialized lenses that are capable of focusing very near the front of the lens to allow you to get up close to your subject.

Sunny 16

Being creative is not just limited to large apertures. As a landscape photographer, one of the areas I like to experiment with is creating starbursts with the sun. The term “Sunny 16” is a memory device used throughout the photography community. For most lenses, if you stop down to f/16 and point your camera at the sun, the rays refract through the aperture blades creating a starburst pattern in your image. The cool thing is that you can see the starburst in your viewfinder or in live view, so there isn’t any guessing whether you capture the feature or not. 

Check out this example from a recent shoot along the California coast. I was excited to capture not one, but two starbursts in this image. 

While it doesn’t always guarantee success, sunny 16, is a fun way to capture a scene. Also, it doesn’t just apply to the sun. You can achieve the effect with a strong enough light source. One final point is that while f/16 is a starting point, I’ve achieved the effect at f/11 as well.

Limited only by your imagination

I’ve shared a few examples of my own, but there are many more possibilities for you to explore the creative aspects of aperture.

In conclusion

At this point, we have discussed both the technical and creative aspects of aperture for your photography. I hope that you have a better understanding of how aperture works and a starting point for using it to create unique photographs that make you proud to show off.

Thank you so much for reading this article. I appreciate your time. Also, if you liked this article, check out this article on the exposure triangle.

Until next time, see you on the trail.