Using the Aperture Priority Mode for Creativity: Lesson 4

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Using the aperture mode for creativity is essential to making beautiful photographs with a specific depth of field. Depth of field means how much of the background you want in focus. Your understanding of aperture opens up a realm of creative possibilities for your photography. While we also use shutter speed and ISO for the correct exposure, for now we will focus on understanding the Aperture Mode.

Aperture Mode

Program Knob
Program Knob

The aperture mode is found on the command dial that we discussed previously. On the command dial, it is indicated as A or Av if you are a Canon user. To change to aperture mode simply turn the command dial to set it. Some cameras may have a lock to release the command dial so it can be moved. 

What is Aperture?

The aperture in a lens allows more or less light into the camera. This is similar to how the pupil in your eye works, by dilating and constricting. Cameras perform this by opening and closing the blade system in your camera lens. A wider opening lets in more light in low light situations while a smaller aperture lets in less light such as in bright light. In a lens this adjustment of the opening is referred to changing the f/stop.

The f/stop System

The f in f/stop means focal length. With each change in a f/stop you are halving or doubling the amount of light entering the lens. You can change this halving or doubling of light by changing not only your aperture, but by changing the Shutter Speed and ISO. This was discussed previously in the Exposure Triangle to get a proper exposure. For the purposes of this lesson, we will only discuss the f/stop only as it relates to aperture.

The f/stop as it Relates to Aperture

The f/stop numbers come from an equation used to work out the size of the aperture from the focal length of the lens. It isn’t essential to know the formula, but understanding the key concepts are.

This scale can be quite confusing to some when learning about aperture. You may have seen these numbers on older film lenses with a aperture ring. Today they can be seen on the LCD screen of your modern DSLR camera.

The f/stop scale is a sequence of fixed numbers starting with 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22. If you notice the numbers increase on the scale. As the number increases the opening becomes smaller. This is called stopping down the aperture. As the numbers decrease the opening becomes becomes bigger and is referred to as opening up the aperture or shooting wide open

A better way to think of these numbers is as fractions. For example we know that 1/2 is larger than 1/22. The same is true that the opening at f/2 is much larger that f/22. This is an easy way to remember what each change makes in the diameter of the aperture.

Not every lens will have all of these apertures.  You may also find other numbers not on the standard f/stop scale. These are third stops. For example, after f/2.8 there may be f/3.2 which is a one third stop smaller and f/3.5 which is two thirds smaller than f/2. 

Wide apertures like  f/1.2 and f/1.4 can make the lens more expensive. These are called fast lenses as they are ideal when shooting in low light.

So, to start putting this together we know that each change in  f/stop on the aperture scale is halving or doubling the size of the opening. When doubling the opening, shooting wider, we allow 50% more light to enter the camera with each stop change. By halving the opening, stopping down, 50% less light enters the camera.  Each change is 1 f/stop. 

How Aperture Affects Your Image

We’re talking about Depth of Field (DoF). This is essentially how much is in focus from the front to back of your photograph. Having a wider aperture like f/2, creates a very narrow DoF. While a smaller aperture like f/16 will have more in focus from the foreground to the background.

Here are examples;

Portrait

An open aperture like f/1.4 to f/2.0 is suitable for portraits where you want the focus to be on the eyes and facial features while blurring the background. This blurring of the background is called bokeh, from the Japanese word meaning to blur. In general, for family shots you need to bump the aperture a bit to around f/4 to f/5.6 for a group of around 6-8 people. For several rows you may need to go to f5.6 to f/8. At f/8 you start to sacrifice some bokeh, but the first priority is to have your subject(s) in focus.

Michelle 1/80, f2.5, ISO 100 at 50mm
Michelle - 1/80, f/2.5, ISO 100 at 50 mm

Isolating the Main Subject

To avoid distracting elements in your photograph use a wider f/stop. In this example I wanted the bird to stand out sharply against a blurred background. Notice this was shot with a telephoto and the bokeh will differ depending on the lens you are using at the time.

Willet - 1/1600, f/6/3, ISO 400 at 500 mm
Willet - 1/1600, f/6/3, ISO 400 at 500 mm

Sharpness from Front to Back

As you can see, everything from the front to the back is in focus in this photograph of the lights in St. Augustine, Florida. For the 8 second exposure a tripod was used. I chose f/16 as this ensured everything would be in focus.

Christmas in Saint Augustine - 8 second exposure, f/16, ISO 100, at 20 mm

Distance Changes DoF

St. Johns Episcopal Cathedral - 1/200, f/9, ISO 100 at 30 mm

The above image was shot from the ground looking up at the cathedral. The distance of the lens from the foreground increased my depth of field resulting in a sharp image at f/9. Being closer to your subject will narrow the DoF, while being at more of distance will increase the DoF.

The Sweet Spot

The sweet spot refers to a lens f/stops it is maximally sharp at. As a general rule, most lenses are sharpest between f/8 and f/11. The assumption of some beginners is that the higher the f number, the sharper the image will be. For example f/22 is thought to be sharper than f/8. Based on some laws of physics this is not true. With very small openings (high f stops) a lens will start to have some diffraction. Diffraction in simple terms is a phenomena that occurs with light when it interacts with an obstacle, in this case the aperture. Because of diffraction the image may appear softer (the opposite of sharpness).

The Sunny f/16 Rule

The sunny f/16 rule is an estimate, like other rules to help you pick an appropriate aperture. This applies to what is called incident light. Incident light is what you see as light falls on your subject, while reflected light is measured by your cameras metering system (to be discussed later). The below table you may find useful in deciding on a aperture for your lighting environment.

From the above table you can see different apertures are used in different conditions. Our distance from the subject, lighting and aperture are elements we consider to be creative. Not to be used alone, but in combination with a shutter speed and ISO to yield a proper exposure.

Suggested f/stop Table

As you follow along we will learn how to use our shutter speed to be creative in the next installment. Don’t forget to subscribe if you haven’t done so already!

Using the Aperture Priority Mode for Creativity: Lesson 4
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Jimmie

Welcome! My interest in photography spans 40 years and started with the purchase of my first SLR. Since then my passion has grown to landscapes, beach scenes, and travel photography primarily. Photography techniques I particularly enjoy are long exposures, and what I call splash art. You can see these on my gallery page if it interests you. Currently, I live on Amelia Island in Northeast Florida with my beautiful wife and our wonder dog, Fuji.