Day 3: Depth of Field and Aperture
Aperture and depth of field are topics that often confuses photographers. The two important things to know with aperture are what each range of apertures can do for you (which relates to the depth of field) and when is the appropriate time to use them.
Aperture is a value, expressed in a unit called f/stops, that refers to the relative size of the opening of your lens when you take a photograph. The bigger the opening, the more light that your camera lets in and the smaller the depth of field (the area of the subject in focus). The smaller the opening, the less light that you camera lets in, but the greater the depth of field (the more of your image that will be in focus).
In the images above, the left-hand image of the crab apple blossoms was shot with a wide aperture (f/1.8), which resulted in a very narrow slice of the photograph being in focus. As the further back flowers rapidly fall out of focus, the light on the very background flowers becomes merely giant circles or bokeh as they are known in photography. The right-hand image of the rose was shot with a narrow aperture (f/22), which resulted in the depth of field (the area in focus) extending through the entire image.
Here's what kept me confused about aperture for the longest time when I started getting serious about my photography and particularly when I started reading a lot of books and articles about photography: the terminology for aperture seemed hopelessly muddled. This is where the fractions come into play. (Now, don't get me wrong. My mother is a math teacher, and I have no problems with fractions, per se, but they definitely interfered with my reading of photography books in this instance.)
Here's what kept me confused about aperture for the longest time when I started getting serious about my photography and particularly when I started reading a lot of books and articles about photography: the terminology for aperture seemed hopelessly muddled. This is where the fractions come into play. (Now, don't get me wrong. My mother is a math teacher, and I have no problems with fractions, per se, but they definitely interfered with my reading of photography books in this instance.)
The f/stop number is actually a fraction, so you can think of the ones used in the example above as 1/1.8 and 1/22 instead. Translate those into decimals, and you have 0.5 (repeating forever) and 0.045 (repeating 45 forever). This means that f/1.8 is actually a 'larger' number than f/22, even though intuitively you would look at them and assume that 22 is a 'larger' number than 1.8. So, when I was reading about larger or smaller apertures, I kept confusing that with what I was reading about wider or narrower apertures. Here it is restated as bullet points just to make it obvious.
- F/1.8 A larger aperture value (larger fraction) = a wider opening = more light coming in = shallower depth of field (much less in focus) and a faster relative shutter speed
- F/22 A small aperture value (smaller fraction) = a narrower opening = less light coming in = a wider depth of field (much more in focus) and a slower relative shutter speed
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| These two shots were taken consecutively at f/1.8 (left) and then f/18 (right). This close to a subject at f/1.8, the depth of field is limited to the front rim of the spoon and the row of stars directly underneath. Patriotic Spoon Reflection by Archaeofrog on Flickr |
What eventually helped me was just to focus on remembering what each aperture could do for me, photographically, and keep it at that. All the larger/wider/smaller/narrower was just too much. If you understand what each end of the aperture spectrum can do for you, you will be well on your way for using aperture to achieve the look you want in your photographs.
One of the best ways to understand aperture is to spend some time looking in through the lens on your camera. Many DSLRs have a small button known as the "depth of field preview" button, often located near or around the lens. (You may have to get out your manual to find yours.) When you press and hold this button, the aperture blades inside your lens close down to the aperture you would be shooting at, and you can actually see the size and shape of the opening.
So, with your camera in Aperture Priority mode, set an aperture of f/22. Now, turn the camera around so that you can see inside the lens. Press and hold the depth of field preview button and watch what happens inside. Now try a middle range aperture value like f/11. Notice the difference? If not, this handy chart by Life in Edit lays it out for you.
What the Aperture of Your Lens Actually Looks Like Inside
One of the best ways to understand aperture is to spend some time looking in through the lens on your camera. Many DSLRs have a small button known as the "depth of field preview" button, often located near or around the lens. (You may have to get out your manual to find yours.) When you press and hold this button, the aperture blades inside your lens close down to the aperture you would be shooting at, and you can actually see the size and shape of the opening.
So, with your camera in Aperture Priority mode, set an aperture of f/22. Now, turn the camera around so that you can see inside the lens. Press and hold the depth of field preview button and watch what happens inside. Now try a middle range aperture value like f/11. Notice the difference? If not, this handy chart by Life in Edit lays it out for you.
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| Created by Life in Edit |
Now that you know the physical part of aperture, the other key is knowing what each aperture can do. Below is a link to a series of four articles about aperture that have previously appeared on Boost Your Photography. Depth of Field: it's more than just aperture shares other factors that influence the appearance of depth of field in your images. Each of the three other articles provides an overview of a specific segment of the aperture spectrum, from the wide aperture end (towards f/1.8), to the narrow aperture end (towards f/22), and to the middle range apertures in between (f/8-f/11).
 Depth of Field More than Aperture |  What an Aperture of F/1.8 Can Do for You |
 What an Aperture of F/22 Can Do for You |  Middle Apertures: F/8-11 |
Once you understand how each section of the aperture spectrum works, it is easy to see how to use each aperture to control the depth of field that you are seeking. Looking for a narrow depth of field and lots of blur and bokeh in the background? Choose a wide aperture. Looking for a wide depth of field with everything in your photograph in focus? Choose a narrow aperture (and probably a tripod).
Summary: Aperture
Understanding aperture will help you better control depth of field and how much of your photograph is in focus. Aperture is also often used for artistic effects and blur. Spend some time shooting with your camera in Aperture Priority mode to familiarize yourself with what different aperture values can do for a given scene or subject. See what a difference aperture can make!
Stay tuned for the rest of the 12 Days of DSLR!
Day 3: Depth of field and aperture
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