Aperture, Shutter Speed & ISO - Understanding the Exposure Triangle

If you are a beginner at photography, there is no rush to jump into Manual Mode. However, if you want to take on the challenge, you will need to understand exposure first. Exposure is a bit complicated, but it is a critical aspect of great photography that can be mastered if you learn the three elements (ISO, aperture, shutter speed) and how these settings are related to one another.

Image courtesy of Pixabay.com

Let me start by saying, understanding exposure and using it to create beautiful images are two totally different things. Just like understanding the concept of time travel and actually time traveling would be two different things! Simply understanding the concept won’t improve your photography unless you practice, practice, practice!

In my beginner groups I am often asked questions similar to “What are the best manual settings for my kid’s soccer game?” My students will request basic settings for different scenarios and the answer “it depends” doesn’t exactly build confidence in my teaching skills. What this demonstrates is a beginner’s limited understanding what manual mode does, what exposure is, and that when using manual mode you can use countless combinations of settings to get the exact same exposure. By the end of this article, you will understand why "it depends" is the correct answer!

First of all, what is exposure?

The term comes from film photography. When light strikes film it starts a reaction and the amount of time the film is “exposed” to the light affects the final image. With digital cameras, exposure is the amount of light reaching your camera’s sensor.
If you overexpose, it means the film or sensor received too much light and your results are much brighter than they should be. Images that are overexposed may have bright white or “blown out” areas. Details in these areas are lost.

When you underexpose, it means the film or sensor did not receive enough light and your final image will be too dark. There will be areas that are completely shadowed and no details can be seen in those areas.

Both overexposure and underexposure can be fixed (somewhat) with editing software. Underexposed images can usually be corrected more easily than overexposed images. Either way, the editing process can result in a loss of quality. It is much better if you can get the exposure correct in the camera by using the proper settings to control exposure.

Left: Proper exposure; Center: Underexposed; Right: Overexposed

How do we control exposure?

This is where the “exposure triangle” comes in. There are three settings that interact and work together, often visualized on a triangle diagram connecting the three terms. The settings are aperture, shutter speed, and ISO.

These three settings are responsible for how much light hits your sensor and therefore control exposure.

Think of the trio as a three-way see-saw. When you change one, you will have to adjust one or both of the other two to keep your exposure correct, or balanced.

We will get into this in more detail further on and I have some tools to help you, but first we need to learn a little about each element of the triangle.

Get free cheat sheets like this one and many others at our website (Click image to go to our Resources pages then click Cheat Sheets).

What is Aperture?
 
The aperture is the opening inside the camera lens. The aperture setting is how big the opening is. The wider open it is, the more light gets in to the sensor. The more closed it is, the less light gets in to the sensor. Take the lens cap off your camera and look into the lens (from the front of the camera). You should be able to see this opening and some curved looking pieces that are spaced around it. These are the aperture blades. They are what move inside the lens to make the opening wider or more closed. The aperture blades work in a similar way to the human eye. Our pupils will become smaller when the light is bright to keep our vision from becoming “overexposed.” The pupil will become more open (larger) when the lights are dim or dark to try to let more light in so we can see into those shadows and areas that are “underexposed.”
 
The aperture scale is probably the most difficult part of understanding exposure because the numbers include decimals and the scale numbers are not intuitive. These numbers are often shown with the letter f, such as f/5. The f/ stands for f-stop (for now that is all you need to know).

The basic aperture scale is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32.
 
The reason it is confusing is because smaller numbers, like f/1 are wider apertures and larger numbers like f/16 are narrow apertures. It is counter to how most people think about number scales. We usually think of larger numbers being related to larger things. Once you understand that this scale is the reverse of what we normally “think” then you will be on your way! You do not need to memorize the scale numbers.
 
In addition to letting in light, aperture also affects the depth of field. Depth of field is how much of your scene is in crisp or sharp focus. Wider apertures create a shallow depth of field. Narrow apertures create a larger depth of field.  
 
More of a scene is in focus with an aperture of f/22 than at f/4. Narrow apertures (big f/#s) are great for landscape photos.

Less of a scene is in focus with an aperture of f/2. Wider apertures (small f/#s) create beautiful blurred backgrounds behind people or flowers. This blur is called bokeh. If the aperture is too wide you can “miss focus” more easily because the depth of field may be so shallow that the front part of a subject is in focus but the back part of it is not.
 
As an instructor, I usually recommend my students begin with Aperture Priority mode. If you are interested in a lesson on this mode and more about depth of field, check out our free lesson here and our article here. Learning Aperture Priority mode is a great first step to getting into full Manual Mode.

What is Shutter Speed?
 
The shutter is inside the camera body. If you have a DSLR it is behind the mirror. If you have a mirrorless, you can see it right in front of your sensor. I don’t recommend poking around inside the camera body to find these as you could damage something or introduce dust inside.
 
The shutter is a like a curtain. When the curtain is closed, no light is hitting the sensor (or film). When the curtain is open, it is letting light in. The shutter speed is how long we leave the curtain open. We can open the shutter (curtain) for fractions of a second, or we can leave it open for minutes.
 
In low light scenarios we want to allow more light to hit the sensor, so we can leave the shutter open longer to accomplish this. If your shutter is too fast (not enough time to let light in), the image will be underexposed. When it is very bright outside using a fast shutter speed will make the shutter open and close quickly so we don’t overexpose the image.

The basic shutter speed scale is 1/8000th, 1/4000th, 1/2000th, 1/1000th, 1/500th, 1/250th, 1/125th, 1/60th, 1/30th, 1/15th, 1/8th, 1/4th, 1/2, 1 second, 2 seconds, etc.

In addition to controlling light, shutter speed also affects motion or blur. A fast shutter speed will freeze motion, such as a hummingbird in flight. A slow shutter speed will allow your images to have motion blur like the soft blurry waters of a waterfall.
 
When using slower shutter speeds you may need a tripod and a shutter remote/release to avoid camera shake. If the shutter is slow and you move, your entire image will have camera shake blur. I recommend a shutter speed of 1/250 or faster for handheld and a good general rule is to use a shutter speed that is at least as fast as the length of the lens. For example, if using a 200mm lens use a shutter speed of 1/200 or faster.

When I give lessons, I usually recommend my students work in Shutter (Time) Priority mode right after they have mastered Aperture Priority. These two modes are great stepping stones to getting to full Manual Mode. If you are interested in a free lesson on this mode, check out our free lesson here and if you want to try some long shutter speed images (known as long exposure images) check out our article here on Fireworks photography (also good for light painting with sparklers or flashlights).

What is ISO?

ISO is the camera sensor’s sensitivity to light. In the days of film, this sensitivity was related to the amount of silver grains embedded in the film. With digital cameras it is electronic sensitivity. As we “turn up” the electronic sensitivity we increase the amount of light or brightness of an image. We explain this term in depth in our article here.

The basic ISO scale is 100, 200, 400, 800, 1600, 3200, 6400, 12800, 25600, and on.

On most cameras the lowest ISO is ISO 100. The sensitivity or brightness is low. We would use this setting when we already have bright light such as outdoors on a sunny day. When we move indoor and away from windows, or into a heavily shaded forest, we need to increase the sensitivity or brightness, so we turn the ISO up.
The ISO scale doubles with each doubling of light: 100, 200, 400, 800, 1600, 3200, etc. Unfortunately, higher ISO settings add digital noise or “grain” to your images. Editing programs can help remove some of that grain.

How do we put the three together?

Exposure is determined by these three elements. Proper exposure requires a correct combination of these three which you can accomplish many different ways. Once you have proper exposure, if you change one element, then you must adjust at least one other element or both to keep proper exposure. Think back to the see-saw when you were a kid. If you change the one side you have to change the other to keep balance. Exposure is a little more tricky because we are balancing three things.

Look at the photo below. The camera was set to Auto so the camera chose my settings for me.

The camera selected ISO 400, Shutter 1/80th, and Aperture f/5.6. The camera will always try to select settings somewhere in the “middle.” This is where Auto mode fails. It doesn’t know what you want and the “middle” settings may not be a fast enough shutter to capture the action or a small enough aperture to get the huge depth of field you want for a landscape photo.

We can take the Auto settings and make adjustments in Aperture Priority, Shutter Priority, or Manual Mode to keep proper exposure AND get the image we want.

In the example above, if there was wind and I wanted to stop the motion of the plant swaying in the breeze, I would need a faster shutter. If I increase the shutter speed, I am opening and closing the “curtain” faster so less light gets in. If I don’t change anything else, my settings would be ISO 400, Shutter 1/250th, and Aperture f/5.6 and my image will end up underexposed like the one below.

By selecting a faster shutter speed, I reduced the amount of light, but I didn't increase the light with any other settings yet. To keep the exposure triangle balanced I will have to adjust one or both of the other elements – ISO and aperture – to make up for the lost light from the faster shutter.

In an underexposed image I need to balance the exposure by increasing the light using my other two settings. I can increase ISO to make it brighter. Or I could open the aperture wider to let more light through the lens. In the image below, I changed the ISO and the exposure is now balanced again.

The final settings were ISO 1600, Shutter 1/250th, and Aperture f/5.6.

How do you know how much to move to keep the balance?

On each of the scales, one movement left or right is equal to halving or doubling of light. The increments along the scales are called "stops." So if you move one element one stop, you must balance another element with one stop. If you move one element two stops, you must balance by moving one element two stops, or by moving both of the other elements but only by one stop each.

We have designed a hands-on tool you can use to practice making exposure adjustments (see our Etsy page), but you can always make your own or use photography apps designed for this purpose. I personally learn better with a physical tool and I use these with my students.

Here’s an example of how it works:

Let's say proper exposure is achieved at ISO 400, Shutter 1/500th, and Aperture f/4. We get this reading by checking the settings the camera chooses when in Auto mode. In the picture below I have moved the sliders to these settings on the scales.

If I want a larger depth of field because I am taking a landscape photo I will need to change the aperture. I will make the aperture smaller (larger f/#) and this will reduce the light entering the camera.

I change the aperture to f/11. I have moved three stops along the scale from f/4, to f/5.6, to/f8, to f/11. This will decrease my light because the aperture is getting smaller and smaller. In the image below I have moved the aperture slider 3 stops to the right side.

Since this is a landscape and I don’t need to stop motion, I can balance the exposure by changing the shutter speed. If I leave the shutter (curtain) open longer I let in more light. How much longer? Three stops!

In the image below I change my shutter from 1/500th, to 1/250th, to 1/125th, to 1/60th on the slider for shutter speed. Three stops to the left. This balances our exposure settings.

But uh-oh! I forgot my tripod! I cannot hold the camera still enough at 1/60th so I am getting too much camera shake.

I can move the shutter speed to 1/125th to be faster (one stop to the right), but then I must change either the aperture or I must adjust the ISO by one stop to the left. I am trying to get more light to balance that faster shutter speed. Since I already have the aperture where I want it for my depth of field and the shutter speed is now set to handle camera shake, I would have to make the change to the ISO (the only element of the three I have remaining). I would increase the ISO by one stop from 400 to 800. I make these changes to my sliders by moving shutter speed slider one to the right and ISO slider one to the left to equal it out.

My new settings are now:

ISO 800, Shutter Speed 1/125th, and Aperture f/11 and I still have proper exposure! Now I can enter these settings into manual mode and my image will have the correct light and it is also adjusted for what I needed to accomplish.

As you can see I could have used a lot of different combinations to make this exposure work.

ISO 1600, Shutter Speed 1/250th, and Aperture f/11 would also balance our exposure.

Landscapes make use of wide angle lenses and narrow apertures. Consider taking a Landscape workshop with us! Or read about Hyperfocal distance an important element to understand for great landscape images (Click image to go to article). Image courtesy of Pixabay.com

Which Mode to Use?

It depends! Even professionals don't use full Manual Mode all the time.  In some types of photography taking the time to fiddle with all these settings means missing the shot. For example with war/conflict, street, auto racing, or wildlife photography the action can happen quickly.

I always recommend starting in Auto Mode. Pay attention to the settings the camera selects. This will start to train you to see how these settings are related. You can get really good at this and even start to predict what settings the camera will use. Then you will be ready to learn semi-automatic modes (aperture priority and shutter priority).

Aperture priority is best when the depth of field is the most important element of the image.

Shutter priority is best when the action or motion is the most important element of the image.

At this link you can find lessons for both Aperture Priority and Shutter Priority Modes.

Use full Manual Mode after you have had lots of practice and in scenarios where you have time to adjust all of the settings without any pressure.

Learn where the exposure compensation buttons are for your camera (check the user guide, if you don’t have one get it here). With the exposure compensation feature you can override the camera’s settings to quickly make the image darker or brighter. Some cameras also offer exposure bracketing. The camera will take a series of shots typically using three or five different exposure levels.

If all else fails, you can correct the majority of issues in editing (except camera shake – that one can’t be fixed in post!).

The Takeaway…

Understanding the exposure triangle as a concept is much different than putting it into practice. The best tip that will 100% improve your photography more than anything else is daily practice. You will have to experiment with different settings and shooting modes and over time you will gain more and more control over your camera. Your images will improve and your brainpower won’t be spent on settings. You will able to put your mind to work more creatively and work on composition and exploring your artistic vision.

Now you know that what mode and what settings you use will "depend" on what you want to accomplish. You can balance the exposure using the three elements of the exposure triangle with many different combinations all "depending" on the light, the subject, and the scene.

If you are interested in some basic starting settings, our Basic Camera Settings Cheat Sheets might help. These cards provide basic lens focal lengths, suggested shooting modes and tips for 6 common photography scenarios.  To learn more see our sales page. You can also purchase an Exposure Triangle tool like the one used above.

Learn more & download free photography lessons and cheat sheets at http://www.focusedcamera.net

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