Photography 101 Tutorial: How To Use Aperture & Depth of Field

Aperture Priority Mode. You might find it on your camera as A or Av for “Aperture Value”. This is my favorite shooting mode, and it’s the one I recommend to anyone who wants to learn to take photos out of AUTO mode.

But first, let me explain what “aperture” means.  Also called F-Stops, and often referred to as f4 or f11, etc., this term is key.   When you press the shutter button on your camera, you are opening the shutter to allow light to pass through the lens and create an image of what the lens sees. It’s just like how your eyes work to create pictures in your brain of what you are looking at.  Aperture refers to how wide or narrow the lens opens.  Lenses these days open in a rounded motion, so your aperture is a circle (or a polygon, like an octagon, that is close to a circular shape).  How wide or narrow it opens determines how much light can get through the lens at one time.  Then your shutter speed determines how long the shutter stays open.  Again, think about your eyes.  Your pupil works like the aperture of your camera.  When lighting is dim, you iris (colored part of your eye) will dilate your pupil (the black part) to a large aperture to allow more light to the lens of your eye.  When you are in bright light, your pupils get really small, like a narrow aperture, to allow in less light.

Note:  Here’s the tricky part to remember, though.  Larger apertures are the smaller numbers on the camera settings, like 1.4 or 3.5 or 4.0.  Smaller apertures are the larger numbers, like 11 or 22.  This is important understand when you are using Aperture Priority mode.

Now let me define Depth of Field (DOF).  Consider the “field” to be your scene, whether it is an actual field or something as small as your tabletop.  Depth of Field refers to the distance within that scene you can see in focus.  A shallow or narrow depth of field will focus on some plane within the full depth of the scene, and the rest of the scene will be out of focus or blurry.   A deep or long depth of field will show all or most of the scene in focus, including the foreground and background.  This is important for choosing an aperture value.

Aperture Priority mode means that you choose your aperture, and then the camera will use its built in light meter to adjust the shutter speed accordingly. The larger apertures (smaller numbers) will deliver a shallow depth of field.  This means that part of your image will be in focus, and other parts will be blurry.  This is nice for portraits or flowers, or any subject that you want to stand out from the background.  You may also want to stick to the larger apertures if you are shooting in low light.

How low/large you can go depends on your lens.  Higher end lenses will have larger aperture options.  Look at your lens.  You might know that it’s, say, a 50-135 zoom lens, but do you see that other number next to your zoom range?   That’s your largest/widest (lowest number) aperture possible with that lens at its shortest zoom setting.  The widest aperture possible will decrease as you zoom in on your subject.  Here’s the camera diagram I posted in my last blog about filters.

Camera Lens Information

Camera Lens Information


So, which aperture should you use?  That’s up to you and your subject. Several factors, including your lens length, your distance from the subject, the subject’s distance from the foreground or background, etc. can determine how the depth of field is focused. Photog super geeks have crazy math formulas to determine which aperture is best, but I’m trying to keep things as simple as possible here (no really, I am!). Luckily with digital photography, you can see the result immediately, and if it’s not the look you want, you can try a different aperture. Hopefully this information will help get you started.

If you want to experiment with a shallow depth of field, start with the largest aperture (smallest number).   Depending on your lens, that might be too much for what you want.  Very large apertures used in closeups of people or objects can give such a shallow DOF, you might have one or both eyes in focus while the rest of the face is blurred.  Professional photographers do this to give an artistic look to portraits, but it it imperative to properly focus.  If you have multiple subjects and want to still blur out the background, try for a mid range aperture, like f5.6.

Smaller apertures (larger numbers) will increase the depth of field, keeping more of both your foreground and background in focus. This is good to use for landscapes, groups of people, or any images where you want to show all the detail of the scene.  Many compact cameras will only go up to f8 or maybe f11, but most DSLR cameras will go up to f22 or higher.  I like to roll with f11 or f22 for daytime landscapes or shots done with a tripod if I don’t mind a longer shutter speed (more on shutter speed in another blog).  At that aperture, I can show crisp details of the foreground and background.   I try to avoid going lower than f11 if I’m doing a landscape or cityscape, but I will consider f8 if I don’t need a really long depth of field and I want to keep my shutter speed fast.

Here’s just one example of how the aperture value can affect an image. Notice how the background gradually comes into focus as I use smaller apertures.

F-Stop Depth of Field Comparison

Aperture Value (Av) Depth of Field Comparison


I am going to skip over the technical math lesson for now about how aperture and shutter speeds work together to let in the correct amount of light for a scene (exposure), but the main idea to know right now regarding shutter speed is that if you change your aperture in Av mode, your camera will adjust the shutter speed to allow in the correct amount of light determined by your meter.  A larger aperture will allow more light in at one time, so the shutter speed can be faster.  A smaller aperture will allow less light in at one time, so the shutter has to stay open longer to let in the correct amount of light to properly expose the scene.

Note: A shallow depth of field doesn’t mean that the foreground has to be in focus while the background is blurred.  If your subject is in the background, you can focus on it and blur the foreground. Or, you can even blur both the background and foreground, while your subject in the middle is still in focus.

Shallow Depth of Field

Depth of Field with both foreground and background out of focus.


Bokeh: Pronounced like “bouquet of flowers” but with the stress on the first syllable instead of the second.  This refers to the blurry areas of a photo that has a shallow depth of field.  Most often, people will talk about bokeh lights in a photo.  Photos where small background lights (like street lights or Christmas lights) are blurry and appear as large balls of light….that’s bokeh.  I wrote a blog about bokeh a while back, but I am going to re-write a new one for my creative series after the Photography 101 series.

Shallow Depth of Field Bokeh with Christmas Lights

Shallow Depth of Field Bokeh with Christmas Lights


This next example is the first picture I ever took (with a Canon Rebel XS, kit lens) after discovering how to use aperture and depth of field. I shot this at f5.6, but since I was close to the subject, you can still see a very shallow depth of field. I was so excited about how broken class on the ground could look so different; dare I say, interesting.  I hope you get the same feeling when you try it out!

Aperture and shallow Depth of Field

Demonstrating Aperture and Shallow Depth of Field


Since my comparison chart above doesn’t have an extreme depth of field to show at the smaller aperture values, here’s an example of  one of my first landscape photos, taken with a Canon Rebel XS, shot at f19.  You can see detail in the hot, dry rocks and bushes right in front of me, as well as the snowcap mountains in the background, and all the windmills in between.

Aperture and Extreme Depth of Field

Aperture and Extreme Depth of Field


Okay, it’s time for you to go try it out!  Pick a simple subject, like a person or an object, and set your big bad camera to Aperture Priority mode.  See if you can blur the background or the foreground while keeping your subject in focus.  Maybe you have to move in closer to your subject, or maybe your subject needs to move further from the background.  Is there a pretty landscape behind your subject?  See if you can get both your subject and the background in focus.  Have fun, and let me know how it goes!


1/24/12 Addition:  I put together another comparison series, demonstrating how aperture affects depth of field for closeups.  These crayons are 1 inch apart, and the closest crayon is approximately 15 inches from the camera.  These comparisons might be helpful to you if you take any type of closeup photos, including head shots, babies, flowers, food, products, etc.

Aperture F-Stop Comparison, Close Up

Aperture Depth of Field Comparison, Closeup, Foreground to Background


Notice that at this distance, even F22 doesn’t bring the purple crayon into perfect focus.  If I had moved the camera farther from the crayons, the results would be different.

Here’s how it looks starting with the farthest crayon in focus.  Keep in mind that the words on the purple (violet) crayon, although in focus, are tougher to read because they are smaller than the words on the closer crayons.

Aperture Depth of Field Comparison, Close Up

Aperture Depth of Field Comparison, Closeup, Background to Foreground


And just for the fun of it, here’s another one, beginning with the black crayon in focus, and the depth of field increases to the foreground and the background.

Aperture F-Stop Comparison, Close Up

Aperture Depth of Field Comparison, Closeup, Starting in the Middle


I hope these comparisons give you a better understanding of how aperture affects depth of field.  Happy shooting!

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