Photography 101: Aperture and Depth of Field

Today, we are going to learn about the final piece of our exposure triangle.  Aperture.

Aperture is a measurement that tells how wide or small the shutter opens when you take a picture.  It is measured in f-stops, and it controls the depth of field.  Maybe we should go back a step and explain depth of field.

Depth of field is the amount of your image that is in focus.  If you have a WIDE depth of field, then you have a sharp, crisp image where everything in the photo is in focus, both far and near.

f 9, 1/250, ISO 100

If you have a small, or NARROW depth of field, only a small portion of your photo is in focus:

f 2.0, 1/60, ISO 500

Do you see how there is just a strip down the middle of the picture where the brownies are in focus, and the edge of the pictures are blurry?  That was intentional.  It’s a small depth of field.  You can do lots of fun artsy shots with a small depth of field…

f 2.0, 1/100, ISO 1000

So, back to aperture.

As I said, aperture tells you how big the opening inside the shutter is when it triggers.  What you need to remember is this:

  • Higher number = smaller aperture (opening) = larger depth of field = more area in focus
  • Lower number = wide aperture (opening) = narrower depth of field = less area in focus
If it’s too confusing the higher, smaller, wider, etc., just remember:
  • higher number – more in focus
  • smaller number – less in focus

Here’s an example of two images taken at the same time, and changing the aperture:

You see, in the image with the aperture of f16 you can see the detail in the rose bush behind the subject, where in the image with f2.5 the bush and fence are blurred.  For single subject portraits, I like having the blurred background, so I will typically use a wider aperture (lower number).  Be careful when shooting multiple subjects, though, because if they’re not in the same plane of focus and you use a wide aperture, one or more of your subjects may turn out blurrier than you’d planned on!

Have you ever noticed the “AV” setting on your camera?  This is the aperture priority setting.  What it does is allow you to set the aperture you want, and the camera will set the shutter speed for you to maintain correct exposure.  It’s fun to play around with if you’re just getting started and want to take some images with nice bokeh.  I would suggest you start with something that doesn’t move around a lot like flowers before you move to something mobile, like your children!

So, there you have it, the final piece of the puzzle.  Tune in next week, when we talk more about exposure and how to put these magic three things (ISO, shutter speed, and aperture) together to gain the perfect exposure!

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About Laura

A Christian wife, mother, daughter, photographer, amateur chef, homeschooler, pretend gardener, cancer-survivor and laundry-hater.

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3 Responses to Photography 101: Aperture and Depth of Field

  1. Shiann November 24, 2012 at 12:17 pm #

    I have forgotten so much of this since moving to digital photography. Thanks for the reminder! I am ready to go out and photograph!

  2. Tony Prower December 12, 2012 at 7:31 am #

    Love your tutorial style, the triangle is a great way to think about exposure. Aperture is a creative arm of that triangle – nicely done with great examples.

    • Laura December 12, 2012 at 10:00 am #

      Thanks for the positive feedback. :)

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