This is not a geometry lesson but the value of this triangle is immense as it gives you the tools to create the perfect exposure. And the perfect exposure is what we all aim at. So how does this exposure triangle help you create the perfect photograph? Let’s take a look at how to create perfection.
What we are going to look at are three controls on your camera, ISO, aperture and shutter speed. You need to understand that each of these impacts on the others. If you change the aperture then you need to change the shutter speed, if you change the ISO then you need to change the aperture or shutter speed.
So here’s how it all works.
The aperture is the scale of numbers on your lens or camera ranging from f2.8 all the way to f22 and above. The widest aperture denoted by f2.8 and the smallest by f22. Aperture controls the amount of light you allow to reach the sensor or film. This determines the depth of field reflected in your photos. Depth of field or depth of focus controls how much the photo is in focus. In a portrait you’d see that the background is blurred out which is created by using a large aperture i.e. f2.8. The opposite is true for a landscape image where nearly the whole image is in sharp focus. Here a small aperture of f22 is used. So how does this affect shutter speed?
2. Shutter Speed
Shutter speed in shown all the way from seconds to thousandths of a second. It determines how long the sensor is exposed to the light reaching it. The brighter the light the shorter the time the shutter remains open to obtain an optimal exposure on the sensor. What you need to understand is that there is an optimal speed for every aperture in order to get a perfect exposure, and vice versa. Lets say for example, that you want a depth of field that shows a fair amount of the image in focus, which could be f8. The light meter says that a shutter speed of 1/125 of a second will give the correct exposure. If you decide to blur out the background a little more by reducing the aperture to f5.6 you effectively double the size of the aperture. At 1/125 of a second you have double light reaching the sensor so you have to reduce it by half to 1/250 of a second. There is a direct relationship with the aperture. The same goes for the shutter speed. If you want to slow it down to 1/60 of a second from 1/125 then the aperture that was correct at f8 needs to be halved to f11. If you increase the aperture then you need to decrease the speed.
This is the sensitivity of the sensor to light. By increasing it from 100 to 400 the sensor is far more sensitive to the light reaching it. This is great for low light conditions where you cannot open the aperture any wider to let in more light so you make the sensor more sensitive. Or, if you need to use a fast shutter speed but the light is too low then by increasing the ISO it will allow you to use a faster shutter speed.
Being able to control your shutter speed or aperture allows you to be more creative as a photographer. Being in control of your aperture allows you to set how much of the image is in focus, i.e. depth of field. Being in control of shutter speed can equally give you more creativity by allowing you to blur or freeze your image. A fast shutter speed will freeze action while a slow speed will blur the action.
On your camera these creative settings are controlled by setting the camera to either aperture priority or shutter priority. Aperture priority allows you to control your aperture while the camera determines the shutter speed. Shutter priority does the reverse allowing you to set the shutter speed and the camera chooses the correct aperture.
There are times where you want the ability to set both aperture and priority. This is done by setting the camera to manual. By getting to grips with these settings you’ll be able to shoot perfect exposures and take complete control of your creativity.