Aperture is the last component of the Exposure Triangle. Knowing what Aperture is and why it is important is key to understanding how to take a properly exposed image. ~CB
Learning Photography: Aperture
We are well on our way to understanding the Exposure Triangle and being able to correctly expose our images. The three components of the Exposure Triangle are ISO, Shutter Speed, and Aperture. All three concepts deal with controlling how the light entering your camera, impacts your image. ISO deals with how sensitive your camera’s sensor is to the light. Shutter speed controls the duration of the sensor’s exposure to light. Finally, Aperture controls the amount of light that hits against the sensor to produce your image.
What is Aperture
The use of Aperture was a logical extension of the study of optics into the world of photography. In optics, the Aperture is the opening through which light travels. In photography, the Aperture is the diameter of the lens diaphragm through which light passes into the camera. The settings on your camera called F-Stops control how wide the diaphragm (or blades) open or close.
I will not bore you with the whole scientific principles behind Aperture and F-Stops, It can get messy, with square roots of numbers and such. Since you are here to learn about photography, and not become a math major, we will focus on two important principles needed to create a correctly exposed image.
Wait! The Smaller Numbers are Larger?
I have to admit, F-Stops were very confusing to me. It wasn’t that I didn’t understand the part about it being the size of the hole allowing light into the sensor, that is straight forward.
What was throwing me was that in study materials I would see suggestions to “shoot wide open” or your largest Aperture setting. F-2.8 or f-1.4 were examples.
Wait a minute! The bigger the opening, the smaller the F-Stop number? What the F-Stop Batman? That made absolutely no sense to me.
One day I happened upon a simple fact that put it all into context for me. You often see F-Stops wrote as f-2.8 or f-22, or even f2.8 or f22. The correct form to write F-Stops in our example is f/2.8 or f/22. Seeing that, it made perfect sense to me that a number divided by 2.8 will be much bigger, than a number divided by 22.
The Effect of Aperture on Your Images
We just learned that Aperture is the size of the opening that allows light into the sensor. What do you think happens when the opening is large compared to when it is small?
A large opening allows light to quickly pass to the sensor for processing, yielding an image quickly. What do you think the details in the picture will look like though? Crystal clear from front to back or maybe just a portion of the photo has crystal clear detail? I don’t know about you, but when I do something a breakneck pace, my attention to detail is usually pretty lacking.
The same holds for the sensor as well. At small F-Stops (large openings) it just doesn’t have the time to capture all of the details.
Now take a moment and think through what happens when the opening is small.
Choose Your Background
Aperture’s effect typically appears on the backgrounds of our images. For images that you want to isolate your subject, one way to do this is to have your subject (or a portion of it) in focus, and everything else not in focus. The lower F-Stops on your camera are used to achieve this. Using F-1.4 through f-6 will give you varying depths of field (how much is in focus) with the smaller numbers giving you less and less in focus.
For images where the entire scene is beautiful, and you want to capture as much detail as possible, f-11 and above are the F-Stops you will need to use. Use these F-stops to shoot expansive landscapes where you want everything to be in focus.
What about the F-Stops between f-6 and f/11? They are sometimes referred to as the “I don’t care about the detail in my background” F-Stops.
Aperture Controls Your Depth of Focus
When considering Depth of Field, I find it helpful to look at the photo as if I were standing directly above it looking down onto the scene, or as if I were a bird flying overhead, looking down. How far does what is in focus extend around the subject? There should be an equal distance in front, and behind the focal point, you chose.
Going back to the mathematical stuff we breezed over, the second important fact is that you need to understand with each change in F-Stop, it corresponds to a change in the light allowed into your camera’s sensor, by a factor of two.
For those of you that already have read my ISO and Shutter Speed blog posts, this should ring a bell. You should hear Big Ben chiming at this point! So this completes the trifecta. With each change in your ISO setting, Shutter Speed, and now Aperture setting, the impact on the light in your image, is either halved or doubled depending on whether you are decreasing or increasing each set.
My Challenge to You
I would like you to take your camera and start with it in the lowest F-Stop available for the lens you are using (probably somewhere around f-2.8). Take a picture of something that is ten feet away from you. Also, make sure there is some distance between it and any background objects.
Take an image for every increase in F-Stop until you have taken a picture at every F-Stop.
Study the photos. In particular, examine the depth of field at each F-Stop. Look to see how much of the image is in focus, and how much is blurred. See the difference across the range of F-Stops? Do you see how the depth of field increase as you go for F-2.8 to F-22? Manipulating Depth of Field will be an important tool in your artist’s toolkit, so take the time now to understand it well.
Wrapping it Up!
So this wraps up the individual components that make up the Exposure Triangle. Knowing what they are is important, but knowing how to use them to your advantage is what takes your work to the next level. Be sure to read “Learn Photography: Exposure Triangle” to use ISO, Shutter Speed, and Aperture to your advantage and properly expose the image you want to capture.
As always, if there are any questions or comments you might have about today’s post, please add them to the comment section below, or you can email me. You can also find me on Facebook, and Instagram.