Exposure Triangle: 3 Key Settings for Great Photography

Exposure Triangle

If you have just graduated from using a point-and-shoot to using a digital SLR camera, learning the 3 main settings of ISO, Aperture, and Shutter Speed will put you on the path toward creating great photographs. A little knowledge about the Exposure Triangle will take away 90% of the mystery surrounding your DSLR camera and help you transition from beginner to ace!

Exposure Triangle

ISO is the measurement of a film’s sensitivity to light. Some of you may remember it as being referred to as a film’s “speed” before the DSLR era took hold of the term. Now it is the expression of a camera sensor’s “signal gain”- its ability to input light and output an image.

Full Frame Sensor
A full frame sensor from a Nikon D800 camera.

Big ISO number = more light/brighter exposure. Small ISO number = less light/darker exposure.


Raising and lowering your ISO number will change your sensor’s sensitivity to light but it will also change your sensor’s sensitivity to undesirable grain and artifacts. The higher the ISO number, the more grain and artifacts you will find in your image. As camera sensors become better and better, these artifacts will become less of an issue. Until then, grain is something to keep in mind when you want to increase brightness in your scene using ISO adjustment alone.


In the example above, the exposures are very similar but, as you can see in the bottom image, increasing ISO to get the right exposure can result in loss of image quality. This is why knowing how to adjust your exposure using your Aperture and Shutter Speed is very important.

Exposure Triangle

If lenses are like an eye then the Aperture is its iris. There are physical blades inside of lenses that form a circle that gets wider or tighter like a pupil.


Big number (small Aperture) = little hole/lets in less light. Small number (large Aperture) = big hole/lets in more light.
Aperture size does more than just increase/decrease the amount of light passing through your lens. It also changes your depth-of-field (how much of your scene is in focus at one time).

Think of your lens as simply a tube whose wide opening starts at a low number, like 1. A bunch of light can pass through that wide circle but it also isn’t very good at focusing on anything. So let’s make that circle inside the tube a little smaller and raise 1 to 2. It focuses a little better on more of your scene but you are letting in a little less light, too. Now just think of that concept all the way up the number chain. Numbers get bigger and bigger and that hole gets smaller and smaller, letting in less and less light but focusing on more and more of your overall scene.


Increasing and decreasing the size of your Aperture is a fast and easy way to increase/decrease scene brightness. However, keep in mind that it also affects how much of your scene you can focus on at once. At 1.8, it is difficult to have both the plant and the statue in focus at the same time, especially when standing fairly close to them. At 11, I can mostly achieve this but my scene would have been too dark if I did not change either my ISO or Shutter Speed to compensate.

Exposure Triangle

The shutter is like a little door that sits in front of your sensor. Open the door and light hits the sensor. The longer you leave that door open, the more light that registers on the sensor.

Shutter Speed

On your DSLR, you will often see on your Shutter dial numbers ranging sometimes from 1 or lower all the way to 1000 or more. This is a measurement of the amount of time the shutter stays open and lets light onto the sensor, 1 being 1 second and 1000 being 1/1000th of a second. This is why it is called your Shutter Speed.

Shutter Speed

More time = more light. Less time = less light.

Shutter Speed affects more than just how long light is hitting the sensor. It also affects how much motion is being registered on the sensor.

When you leave your shutter open and let in all that light, you are also “letting in” movement. It can be difficult to hand-hold your camera and keep your image sharp while leaving your shutter open for longer than 1/125th of a second (depending on how good your surgeon’s hands are). While your shutter is open, think of it as “burning” the scene onto your sensor. If you are moving around while that scene is trying to burn, the lines are going to get blurred. Likewise, if your subject is moving around while that light is trying to burn in, you are going to end up with unsharp results with a lot of motion blur. Fast shutter speeds, where light is hitting the sensor for a shorter period of time, are good for reducing brightness and for freezing action.

Shutter Speed

Freezing action is as simple as increasing the Shutter Speed. However, it can come at the cost of exposure if one doesn’t compensate by either lowering the Aperture or raising the ISO. In the image above, the scene is exposed well enough at ISO 800 with an Aperture of 1 and a Shutter Speed of 1/60th of a second. As soon as the child begins to move, however, you start to see the motion blur. The Aperture is already as low and large as it can physically go and is bringing in the maximum amount of light possible through the lens. If we wanted to reduce motion blur here, it would require increasing the Shutter Speed to something more like 1/125th of a second but that would make the scene darker. In this situation, we would have to raise the ISO to compensate.

Sometimes our scenery blesses us with perfect ambient lighting and, most of the time, your camera will know how to expose a scene for you in Auto mode. However, in order to take advantage of the artistic merits of your Aperture’s depth-of-field and your Shutter Speed’s expression of motion, you will want to remember the Exposure Triangle. Once you have mastered using ISO, Aperture, and Shutter Speed to control natural light, you will then be able to enjoy the introduction of artificial light in your photography and take your images to the next creative level.

by Alex Huff of BorrowLenses.com

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