The Exposure Triangle. The key to creative control of your camera

December 16, 2014  •  Leave a Comment

I am often asked by aspiring photographers why the expensive camera they just purchased does produce photos of a better quality than the point and shoot model they replaced. Almost every time when I look at their camera it is set to either a program or auto function. When I ask them if they have ever shot with the camera in manual mode I am faced with a look of fear or confusion. There seems to be an apprehension among novice photographers of running their cameras in manual modes even though manual control opens a door to the world of creative possibilities. Mastering the camera controls allows for not only speed in determining settings for proper exposure but also the confidence in those settings. More time can be spent on composition and creativity.

When it comes to creativity the first rule is there are no rules. When it comes to physics, geometry and optics the rules are rigid. So, before you spin the knob of your camera and jump into manual mode, a basic understanding of the the fundamentals of camera control is in order.

The Holy Trinity of Proper Exposure

The Exposure Triangle gives a graphic representation of the relationship of time, lens aperture and sensitivity to light. Used in combination this triad allows the photographer to take control of exposure, stopping action of the subject, the amount of light available to the camera sensor and how much of a scene is perceived as in focus.

Exposure

Controlled by the shutter speed of the camera, exposure is the length of time the camera is allowed to capture the scene. Exposure is expressed in time. Typical full step shutter speeds are 1/8, 1/15, 1/60, 1/25, 1/250, etc. although timed exposures can last for minutes, even hours. Shutter speeds are doubled or halved as you increase or decrease speed. Some camera manufactures break their shutter speeds into increments of 1/3rd of a step allowing for more precise exposure.

Aperture

This setting allows or restrics the amount of light entering the camera during the exposure. If you were to take the camera lens off of your camera and turn it around you would see a hole created by metal leaves that can be set to a various size openings. These apertures are called f stops. The larger the aperture, the more light is allowed into the lens. Closing the aperture down creates a smaller hole and restricts light. Aperture directly affects the depth of field in your image. Depth of field controls how much of the image remains in focus in front and behind of the actual point where the lens is focused to. F stops can be broken down to a 1/3rd of a stop but on many cameras and lens barrels full stops are shown as f2.8, f4, f5.6, f8, f11, f16, f22, f32. It may be confusing for you to grasp f stops at first blush as smaller numbers (2.8) indicate larger aperture openings. It is worth noting that apertures are doubled with every other stop.

Sensitivity

This number represents the sensitivity setting for the image sensor on your camera. The number is followed by either ISO or ASA. For those so inclined Wikipedia has a wonderfully in depth and sedative inducing explanation on the difference between the ISO and ASA measurement scales. For the rest of us the two can be considered the same. Sensitivity is expressed in values such as 100ISO, 125ISO, 200ISO, 250ISO, 400ISO, 500ISO, 800ISO, etc. Used to describe sensor sensitivity today, the ASA scale was used to express speed values in the days of film. It was a sensitivity scale for film emulsions and described by how fast (sensitive) or slow (insensitive)  film was to light. The higher the value the more grain was apparent in the negative. In the digital age lower sensitivities will show less noise and higher values increasing noise. Modern sensors are very good at controlling noise up to very high ISO values of 1600ISO and beyond.

Now, let's see how we can use these three controls to our creative advantage.

Everything in Life (and photography) is a Compromise

The key to control is compromise. You have three powerful tools available to create an image. The first question to ask yourself is what are you trying to accomplish? Do you want to stop the action of a rider jumping a horse? Maybe it's a room where you want the entire space to be in focus. Your goal may be to draw a viewers attention to one particular point of an image. Below are images that take on these various challenges.

2014 © Dave Tusia / Tusia Photography

This photo to the right is from the Woodstock Horse Show in Woodstock Connecticut. The goal here was to capture the riders as the horse begins to leap the fence. Speed is the priority. You need to stop the action. To do this you are going to set your shutter speed as fast as possible for the lighting conditions you are working in. Because of the overcast day I selected 1/1000th of a second. If we cut the light to the camera with a fast shutter speed your going to have to make a compromise somewhere else. Is it going to be the light sensitivity to the sensor or the amount of the image that remains in acceptable focus. Because our interested is in the rider and horse we can (and want) the background of the image to be out of acceptable focus. The goal is to have the viewers attention drawn to the rider.

When I photograph a jumping shot such as this I lock my focus on the white horizontal post and time the jump to determine when I fire the shutter. I need a little bit of wiggle room with the depth of field as the horse and riders heads land in a slightly different spot each time, leaning a bit forward or behind the post I am locked on to. I chose an f stop of f8. It is a good compromise for sharpness and depth of field for the distance I am shooting at and the telephoto lens I was using.

With the shutter and f stop set I will now make a compromise on my ISO.  It worked out to 500ISO, more than acceptable. These numbers changed throughout the day as the sun poked through the clouds occasionally and I bracketed frames to maintain proper exposure. 


The next example is a hotel room at Foxwoods Resort Casino in Mashantucket Connecticut. These are large, contemporary suites with a lot of eye appeal and the goal was to not only capture the look of a naturally lit room but to show the depth of the room without the heavy distortion you see in many hotel room photos. Because nothing is going to be moving in the image, shutter speed is not a priority, though it needs some careful attention to make sure the landscape is not completely over exposed. The priority with this shot is depth of field. I want the image in focus from front to back. I chose an f stop of 16. By using a 28mm lens and focusing to the middle wall I am getting acceptable focus from about 3 feet in front of the camera to the rear wall.

Now we can work on the shutter speed and ISO. Because this image may be enlarged to a massive scale for a billboard I decide to use an ISO of 50. I want this image as rich in color and noise free as possible. With a ISO of 50 and an f stop of f16 selected I then point the camera towards the window and read the exposure. It worked out to 1/10 of a second. This tells me how long the shutter will need to remain open to expose for the landscape. At this point we have used the exposure triangle to gives us our exposure for the landscape.

The issue that needs to be addressed now is that when you recompose the image the room it will be under exposed because of light fall off. To correct for this multiple daylight balanced photo flashes are set up throughout the room and metered to match our f stop of f16. When the shutter is released the flashes instantly provide the correct fill flash in the room and the shutter is slow enough to capture the ambient light of the landscape and ambient light entering the room. The result is a fairly accurate representation of what the room looks like to the eye. The skyline is a bit overexposed but that was a compromise made to keep the trees from becoming underexposed.

 

For the Praying Mantis image I was concerned with one thing. Capturing it's face. I wanted emphasis there and a quick drop off of focus in front and behind.

F4 was selected to give me the shallow focus I required and a 105mm macro lens gave me the magnification and working distance optimum for working with an insect. From where I was standing I ended up with less than 6 inches of depth of field. Seeing that I did not have an insect wrangler to keep this little guy from wandering around I needed to select a fast enough shutter speed to stop the action of it's movements. Patience in waiting for the mantis to settle down and few test shots determined 1/100 of a second was enough. With f stop and shutter set I could then meter the subject to determine the ISO to be 400. Once I had my exposure nailed down it became a game of getting the Mantis to move into the position of my composition. This took a bit of time as I wanted to get one of the red flowers into the frame to counter the green foliage and brown of the insect. The result? What I feel is as close as you can get to a Praying Mantis with a personality.

The Sunny f16 Rule

When working outdoors there is a process that can assist you in getting accurate images very quickly. It is referred to as The Sunny f16 rule. The rule states that if a subject is lit by bright sunny to a lightly clouded sky, you can predict proper exposure by matching your ISO and shutter speed settings while your f stop is set to f16. An example would be 100ISO 1/100 shutter speed and f16. This will get you very close if not the proper exposure. For a rounded ISO of say 200 you can average 1/125 or 1/250 and then adjust for the scene as needed. Adjustment can be made for snow, sand or over cast days by using the following guidelines:

Sand / Snow : f22

Bright Sun : f16

Partly Cloudy: f8

Dark Clouds: f5.6

These are all loose guidelines. Each scene is different so taking one or two photos and slightly varying the exposure (refered to as bracketing) will yield the best results.

We have only scratched the surface on how to correctly select proper exposure. Distance from subject, lens selection, dealing with back lighting, outdoor fill flash and hyperfocal distance are many other items that need to be addressed in obtaining an optimum balance exposure. Learning to manipulate of shutter speed, aperture and sensor sensitivity are key when determining proper exposure. They are the the building blocks to creative photography. 

 


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