Beyond Auto: Aperture – Part 2

Going Beyond Auto - Aperture Part 2

You just learned more than you ever wanted to know about aperture in Beyond Auto: Aperture – Part 1, now what does that have to do with my photos?  The answer is that it has everything to do with your photos!  All cameras have an aperture, yes even that smartphone in your pocket.  Some of them we can manually adjust, and some only run on auto.  We are going to assume that you have a camera where you can adjust the aperture, and that you read part 1.  You may have a DSLR, or even a point-and-shoot camera with manual control…either way, let’s talk about aperture and your photos.

Why do I need different Apertures?

The aperture setting you choose depends on the outcome of the picture you would like to take.  Having a fast lens, or a wide aperture, allows you to get more light through the lens and onto the sensor.  Not only does that allow you take photos when it is darker, but it gives you creative control on the outcome.  If you want one of those portraits of your child or significant other (or dog, flower, whatever you are eating, you get the idea) where the subject is in focus and everything else isn’t…that’s controlled by the aperture.  Or maybe you have hiked out to a remote location and are staring at a breathtaking view of lakes, fields and mountains and you want to capture it all as you see it, aperture comes into play here as well.

Selecting the correct aperture makes a world of difference on the end result.  From brightness, to depth of field, aperture is the key to capturing the perfect image.

Capturing Light and Shutter Speed

The main purpose of aperture, and I have said it a few times already, is to allow a certain amount of light to pass through the lens and hit the sensor.  Forgive me for sounding like a broken record, but I really want you to understand what aperture is all about.  With that in mind, it can be said that aperture is used to control how much light you want to hit the sensor.

For instance on a bright sunny day, about 3PM, I want to take a picture of my daughter playing in the grass.  With that known, I could choose a safe aperture of f/8 to capture her and everything around her in focus.  With my camera set in Aperture Priority mode, the camera would figure out an appropriate shutter speed of around 1/500th of a second for the correct exposure.  But if I want to now capture her cute smiling face and have everything else be out of focus, I would shift to f/4 and let the camera tell me something like 1/1000th of a second for shutter speed.

You see, there is a direct correlation between aperture and shutter speed.  Your ISO setting and the amount of light also play into this, but we will get to that another day.  However, if the light is bright, a faster shutter speed is needed to compensate for the amount of light passing through.  The same works for a smaller aperture and a slower shutter speed to attain the proper exposure.

What about in a darker room inside your home or office?  You will probably need to open up your aperture as wide as possible just to get enough light in.  Unless you are using a lot of artificial light, a slow aperture of f/8 or slower may yield an image that is too dark regardless of shutter speed.

What is most important to note is that aperture and shutter speed play well together.  You need to find the perfect balance of the two in order to get a good image.  If you are trying to stop down your lens (using a smaller aperture) to gain focus, but your shutter speed gets too slow, you will end up with a blurry shot.  However, if it is too bright when you are trying to use a wide open aperture, your camera may not be able to flip the shutter fast enough to expose the image correctly yielding an over-exposed shot.

Depth of Field

The second main function of choosing the correct aperture is to determine the depth of field(DOF) for your photo.  The depth of field is the area within your photo that is in focus.  This can be seen when you take a picture with a blurry background, or a sharp landscape image.  Aperture is a key factor in determining depth of field, but it is not the only factor.  Focal length and focus distance also play a role in depth of field.

Typically, when you use a wide aperture, around f/2.8, you will have a shallow depth of field, or a very small area that is in focus.  With that said, using a narrow aperture, around f/16 will provide you with a deep depth of field.  However, as I just mentioned, aperture alone isn’t the only factor at play.  But for the sake of this post, let’s just talk about aperture and its role in the depth of field game.

Shallow Depth of Field

Depending on the lens you have available, if you want a picture with a shallow depth of field (blurry background) you will want to use the widest aperture possible.  This could be anywhere from f/5.6 to f/1.4 depending on the lens you have.  The wider the aperture, the shallower the depth of field will be.  To achieve a good DOF portrait, have your subject stand a few feet away from the camera and focus on their eyes.  Depending on your maximum aperture, this will render their face in focus with the potential of blur starting around the middle of their ear.  The key is to focus approximately 1/3rd of the way into your subject to ensure the depth of field captures the area sharply.

Canon Rebel XSi - 50mm - ISO 100 - 1/1000 sec - f/1.8

Canon Rebel XSi – 50mm – ISO 100 – 1/1000 sec – f/1.8

If you find that not enough of your subject is in focus, you can simply close the aperture a stop or two, and decrease the shutter speed to compensate if you are in manual mode.  Or you can simply move further away from the subject, but we will talk about that another time.

Kevin Heffner

Canon 6D – 105mm – ISO 100 – 1/640 sec – f/4

Deep Depth of Field

You find yourself standing in front of a huge lake with a mountain range in the background and you would love to take a crisp photo of what is before you just as you see it, so you will need a deep depth of field.  A good place to start is f/8 or f/11 for this type of shot, however you may want to use f/16 if it is light enough.  If you find yourself running out of light, then your camera will use a slow shutter speed to make up for the aperture being so small and you will need a good tripod so your photo is clear.

Costa Rica Sunset - Going Beyond Auto_5534

Canon Rebel XSi – 75mm – ISO 800 – 1/320 sec – f/8

Once again, focus about 1/3rd of the way into the scene you are taking a picture of to ensure a good crisp image.  Don’t worry, I will write a post that explains why you should focus that way and all the math that goes along with it later.  For now I am trying to keep it simple so I don’t scare you back to Auto mode.

Hoover Dam - Going Beyond Auto_3713

Canon Rebel XSi – 28mm – ISO 100 – 1/250 sec – f/8

The main thing to take away from this is if you want everything to be sharp in your photo, close down the aperture starting at least at f/8, but f/11 and f/16 are better.  If you want a nice blurry background, open your aperture as wide as it can go, ideally around f/2.8 or f/4.


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