For many beginners, the relationship between aperture, exposure time and ISO sensitivity can be confusing. For simplicity, the relationship between these parameters is expressed using an exposure triangle. The most important thing for you to remember is that if you change one parameter of the exposure triangle, then you must change the setting of another parameter of the exposure triangle in the opposite direction to maintain the correct exposure. This procedure will maintain the correct exposure setting. You’ll learn how it works together in this article. But first, take a look at the following infographic.
Exposure triangle – ISO
ISO expresses the sensitivity of the camera’s sensor to light. The figure shows the base of the triangle. Higher ISO values mean higher sensitivity. Low ISO values mean lower sensitivity of the camera’s sensor too light.
The ISO scale is a numerical series of multiples of adjacent values. The higher value is always twice the lower adjacent value. Setting the ISO scale by one stop doubles the camera’s sensitivity to light. Decreasing the ISO value by one step results in a one-stop reduction in the exposure of the photograph.
Exposure triangle – shooter speed is exposure time
Shutter speed is the time it takes for light to hit the camera’s sensor. It is usually given as a fraction of a number in seconds. The exposure time is shown in the exposure triangle in the opening image on its right arm.
If we want to double the amount of light exposure then we must double the exposure time. For example, changing the shutter speed setting from 1/60 s to 1/30 hits half the light on the camera chip. Changing from a shutter speed of 1 s to 1/8 s will reduce the exposure by three steps. Why? From 1 s to 1/2 s is one step. The next step is 1/4 s and the third value in a row is then 1/8.
Exposure triangle – aperture number
Aperture indicates the size of the circular hole in the lens through which light falls on the camera chip. The larger the hole, the lighter falls on the chip. In fact, each time you double the area of this aperture, we double the amount of light or increase the exposure by one step and vice versa. The introductory figure shows the left arm of the triangle.
|f / 1.4||f / 1.8||f / 2.8||f / 4||f / 5.6|
Small aperture values correspond to larger apertures and vice versa.
To double the area of the hole, the previous value must be divided by the square root of two (1.414). That’s why the aperture steps aren’t nice round numbers. Remember that the area of the circle is = (π / 4) D2
|+/- EV||Aperture number||Shuter speed||ISO|