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Aperture and Depth of Field

Posted on September 17, 2014 by Mark Fuentebella

In photography the Exposure Triangle is probably one of the most fundamental aspects. Basically what this means is that there are three major components of photography which are shutter speed, aperture, and ISO. In this blog post I'll be talking about only about aperture. All three are equally important, but to learn all three at the same time could be a little overwhelming with so many variables.

What is the aperture?

The aperture is the hole in the lens that allows light onto the sensor of your camera. Now the size of the hole determines how much light is allowed into the camera. The size of the hole is measured in what are called "f-stops." On your camera it will usually say something like f/4. One confusing part about these f-stops that just takes some getting used to is that the lower the number is the bigger the aperture hole is. So an f-stop of 1.8 means that the hole is much bigger.

Canon EF 85mm f1.2L opened to f1.4

Canon EF 85mm f1.2L opened to f5

Canon EF 85mm f1.2L opened to f16

So what does changing the aperture do?

Aperture allows you to control how much of your image is in focus. This is called "Depth of Field." A bigger aperture (lower f-stop number) will give you a more shallow depth of field. This means that if you focus on an object in front of a background, the object will be sharp and the background will be very blurry. This is very helpful for portraits because it allows viewers to look at the more important thing in your picture: the person.


On the other hand, a smaller aperture (higher f-stop number) will gave you more depth of field, meaning more things in your photo will be in focus: the foreground, mid-ground, and background. This is useful for landscape photos because you want everything in your image in focus.

For all the following example pictures, I used a Canon EOS 5D Mark III with an EF 50mm f1.4. I set my camera to to Av for Aperture Priority. What this does is it allows me to choose what aperture I want to take a picture with and the camera will choose the rest to get the right exposure. 

 So for the three images above I was shooting with my aperture at f1.4 (large hole) and as you can see there is only a limited section of the brick wall in focus. What I did for each picture is just set where i wanted the image focused. You can see how I focused first on a closer section of the wall and moved the focus to the farther section with the PVC pipe.
 In the picture above, I shot with  my aperture at f10 (medium sized hole) and as you can see there is a much larger noticeable area of focus from halfway towards the back to the dumpster.



 In the two pictures above, I set my aperture to f1.6 (large hole) and moved my focus from the first post to the third post.
 In the photo above, the aperture was set to f7.1 (medium size hole) and as you can see more of the image is in focus. You don't need to set your aperture all the way to 22 to get everything in focus.

One more tip for your aperture settings is that there is a button on your camera called the Depth of Field Preview button. It is the button closest to your lens that is NOT the release button. When you press this button, depending on your aperture setting, while looking through your viewfinder will sometimes make things dimmer. The dimmer it is the smaller your aperture is set to. Although it is dimmer it will show you how much is in focus. It makes it dimmer for reasons I'll go over in another blog post, but long story short it's part of the Exposure Triangle in which a smaller aperture requires a longer shutter speed. But anyways, this button does exactly what its called. It allows you to view your depth of field with your set aperture.

Depth of Field Preview button on the T4i located just below the lens release.
Stay tuned for a blogpost about how aperture and shutter-speed act with each other!

Blog and Photos by Mark Fuentebella

If you are not familiar with our camera store, we are located in Dubuque Iowa, and specialize in new and used camera equipment, as well as camera rental, lens rental, and photography classes and photography workshops. Feel free to contact us at (563) 845-7207, or visit our website at www.everyphotostore.com 
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