Hello! Today we are going to discuss aperture which affects depth of field. Depth of field is what creates those beautiful bokehed or blurry backgrounds like the image above. If you notice the little girl in the image above is the only thing in the picture that is tack sharp, everything else behind her is blurry. This technique allows the viewer’s eyes to be drawn in to the subject for a more memorable image. Now there are a couple of other factors that affect depth of field besides aperture such as focal length, focal plane, distance from subject, and distance from background, but aperture is a good place to start. We’ll talk about depth of field as its own topic a little later for a more detailed examination.

Aperture as a Component of the Exposure Triangle

As a component of the exposure triangle, aperture has to be considered to compliment both the shutter speed and the ISO to achieve proper exposure. Aperture refers to how wide the opening is in front of the lens as you snap the picture. I like to compare it to the pupil of an eye. If you walk into a dark room, your pupil gets larger so it can let in more light. This helps you see better in a low light environment. But if you are in a very bright environment, such as outside on a sunny day, your pupil gets smaller to let in less light. Your pupil manages light in this way to always give you the best “picture” possible. Your eyes are adjust automatically for you to either let in more light or less light depending on your environment. Aperture works similarly. A larger opening = more light and a smaller opening = less light. If you are outside on a bright sunny day, you may choose to have a smaller opening to let in less light simply because you don’t need as much light going into the camera to take a proper exposed picture. Inversely, if you are indoors, you may need to open up your aperture to let in more light for your picture to exposed properly.

Since we already talked about shutter speed and how a fast shutter speed lets in less light and a slow shutter speed lets in more light, you can see how aperture and shutter speed could play to together in the exposure triangle. For example, if you are photographing young kids, I mentioned my rule of thumb is to shoot at a shutter speed of 1/250 or higher to freeze motion, but that may not give you enough light to expose your picture properly. To compensate for the faster shutter, you will need to use another facet of the exposure triangle to allow for more light, such as aperture. You could adjust the aperture so the opening is larger which would let in more light. That way you could have a higher shutter speed. As you adjust one component of the exposure triangle, you will always be adjusting the other two as well to allow for the most ideal light to enter your camera for a balanced image.

So far so easy, right? Well, here is the part I got hung up on when I was first learning this concept. How aperture is measured. Aperture is measured in f-stops and the largest opening has the smallest number and as the opening starts to close down (get smaller) the measurement number increases. So in a nutshell its opposite: small opening: large number and large opening: small number. See the picture below for a visual representation.

(Image created by Esmer Olvera. Link to original image, Aperture. Link to license details. No changes made)

Aperture as a Component of Depth of Field

Aperture affects your depth of field. Basically the larger the opening (smaller the measurement number) the shallower your depth of field (less of an area in focus). And the smaller the opening, the larger the area that is in focus. I am not a technical person to go into all the particulars of why this is this way but knowing this and understanding how small changes to the aperture can adjust the overall look in your image is important. The other thing that is good to notice is how physically close you are to your subject. Your proximity to your subject will also affect how quickly your image gets blurry past your focus point regardless of aperture setting. You will discover that if you are physically closer to your subject you will likely need a higher aperture setting to ensure enough of the image in focus. The best thing to do to really learn these two things is to play around with it.

 Key Learnings

• Aperture is the second component in the exposure triangle
• Aperture is the opening in front of the lens that opens and closes, similarly to the way your pupil works in your eye
• The larger the opening, the more light that is let in, the smaller the opening the less light
• Aperture is most often measured in f-stops and the smaller the number the larger the opening. The larger the number the smaller the opening (opposite)
• Aperture affects depth of field. The larger the opening the more shallow your depth of field. The smaller the opening, more of the image will be in focus

Practice

For practice adjusting aperture, move your dial to the “A” or “AV” mode for aperture-priority. Look up in your manual if you are unsure what setting that is since it may vary from manufacturer to manufacturer. By using aperture-priority mode, you camera will allow you to manually adjust your aperture only. The camera will adjust the other two settings, shutter speed and ISO automatically. This way you will really be able to focus on the aperture setting solely and observe how it changes the appearance of your picture as you adjust it.

The first exercise I would recommend is to find a few items and line them up. First, set your aperture to a low f-stop and focus on the first item in the group and take a picture. Do the same thing a few more times but increase the aperture each time keep your focus point on the first item in each shot. Now compare your shots. What do you notice about the pictures?

In my example, I have my camera on a tri-pod to ensure that the photo is exactly the same. I am using a Nikon a610 with a Nikkor 24-70mm lens. I have a shutter speed of 1/40 and I am starting with an f-stop of 2.8 and moving up from there while adjusting my ISO to compliment the increase in aperture to maintain exposure. I am also using my speed light set to manual at 1/4 power. We will talk more about supplemental light in a later post. But basically, I wanted to keep a fairly low ISO so I needed to supplement the light and the reflector provides a soft clean bounce. Pull-back of my setup pictured left. 

The second exercise I would recommend involves the same items from the first. This time leave your aperture on the low setting but change your focus point from object to object. What changes? Notice that your depth of field falls off on both sides of the focus point? If you are focused on the middle to last item, the items in front start to blur and if you focus on the front item, the back items are blurry. Interesting, right? If you look at the shot of the cupcake in front of the cupcake tower on the table, you will notice the table in front as well as the tower behind are both blurred. This is an example of depth of field.

The third exercise I would recommend is to set an object up on a flat surface and then your aperture to a fairly low setting (ex. f stop 2.8). Start shooting as close as you physically can in relation to the object. Take a picture. Then back up a few foot but leave your aperture at the same setting. Do this a few times. What happens to your depth of field?

Tip

I love the way the blurry background looks in images so I will often shoot wide open (large opening) to get a beautiful bokeh. If you adjust your aperture first, then you can set the other settings to compliment your aperture for your desired image look and feel. Just keep in mind shutter speed if you are working with kids.

This is my second tutorial on aperture….here is my first one for more reading: Aperture: The Blurry Background Tutorial 

Most of these examples were taken at my second daughter’s first birthday party. For some tips on taking detail pictures at a party, please visit my post, How to Take Detail Shots that Count.