What is Exposure Triangle in Photography?

Exposure is the amount of light that reaches the Sensor or Film. If too much light reaches the Sensor, the photograph will be overexposed – that is it will be too bright, washed out with no detail. Whereas with too little light the photograph will be underexposed – that is dark, grainy and will lack in detail and contrast.

For us to get a clear and detailed photograph we need to have the correct exposure. When you use a Camera in Auto mode, the internal computer takes care of the exposure for you. However, good Photographs are not just made with correct exposures, you need a creative element that can only be achieved by turning off the Auto mode in the Camera.

The 3 main functions that control the exposure Shutter Speed, Aperture and ISO. When used together, these 3 functions help you get a creative shot within the capabilities of your camera. Let us review each of these functions.

Shutter Speed: Shutter controls the amount of time the camera has to let the light in and time to capture the movement. It works like a curtain on a window. If the shutter is on for a shorter duration (say 1/500th of a second) it will result in a shorter exposure time, and thus “freeze” an action. It also means less light will get in. However, if the shutter is on for a longer duration (say 1/25th of a second) it will result in a longer exposure time, and thus “blur” an action. It means more light will get onto the sensor.

Aperture: It controls the size of the lens opening. It is just like the Iris of the eye. If the aperture value is smaller number say f/2.0 it means there is a larger lens opening allowing more light through the camera onto the sensor. Whereas if the aperture value is a bigger number say f/16 there will be a smaller lens opening thus allowing less light onto the sensor.

ISO: It controls the sensitivity of the sensor to light and the amount of grain / noise on a photograph. Consider ISO like a magnifying glass on a newspaper. The closer you get the grainer the image, thus the higher the ISO the grainer is the photograph. If the ISO number is small say ISO 200, the sensor will be less sensitive to light, i.e. allowing less light and will have a finer grain / less noise on the final photograph. Whereas, if the ISO number is high say ISO 1600, the sensor will be more sensitive to light, i.e. allowing more light and will have rough grain / more noise on the final photograph.

The Exposure Triangle:

Consider the following hypothetical situation:

The Window: Image your Camera like a very dark room with an electro mechanical window with Shutters than can open and close. You can control with a switch the amount of time / duration the Shutters of the window are open (shutter speed).

Window Size: Consider this as the size of the window. The bigger the window more lights gets in and vice versa which you again can control with another switch.

Sensitivity: No imagine you are inside the very dark room wearing a Sunglass (generally you will not do this, but all for the sake of photography). Since you have the dark eyepiece on your eyes will be less sensitive to sunlight, i.e. like low ISO.

Now there are a number of ways to capture the “perfect” amount of light in the dark room. You can increase the time that the shutter is open (if the light is low outside) or decrease the time the shutter is open (if it is very bright outside). Or you can increase the size of the window (increase aperture) or you can take off the sunglass (a bigger ISO) to increase the light. This example hopefully gives you some hint towards the Exposure Triangle.

Now, while with the Automatic mode your camera can give you more or less perfect exposures every time but mastering the art of exposure manually takes a lot of practice. It is a juggling act and one needs to adjust these three settings on the go for achieving a perfect exposure. One thing you need to keep in mind that each of these three elements impacts the exposure differently and has “side effects” too.

As, we have seen the three elements in photography have to be combined so we can get the best of results. Each element of the Triangle is important and must be select in unison.

Camera Exposure Modes:

Auto: Camera automatically selects the exposure settings by applying the best Shutter Speed, Aperture and ISO settings.

Program (P): You choose the ISO & Exposure Compensation settings and the Camera correspondingly selects the Aperture & Shutter Speed for a perfect exposure.

Aperture Priority (A or Av): You choose the Aperture & ISO and the Camera correspondingly selects the Shutter Speed for a perfect exposure.

Shutter Priority (S or Tv): You choose the Shutter Speed & ISO and the Camera correspondingly selects the Aperture for a perfect exposure.

Manual (M): You have total control over the Shutter Speed, Aperture & ISO and you are in total command over the Exposure and here understanding and mastering the Exposure Triangle helps you over the creative control of your Photograph.

Bulb (B): Similar to Manual mode where the shutter speed needs to be over 30 seconds. You can control the Shutter Speed by a remote release switch or by the duration you hold the Shutter button.

Exposure Simulation:

Although you should experiment with Exposure Triangle in Manual mode with a real Camera but there is a wonderful piece of software at http://camerasim.com/apps/camera-simulator/ to help you get going at the comfort of your desktop.