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[Lesson 1] How Exposure Works

Exposure, which refers to the brightness of a photo, is determined by the mutual interaction between the shutter and the aperture. Obtain a good understanding of exposure to control how your image turns out. (Reported by: Ryosuke Takahashi)

The Basics of Exposure

The amount of exposure is determined by the aperture value and shutter speed

"Exposure" refers to the brightness in a photo. The brightness of a photo is determined by the total amount of light falling on the image sensor, while the shutter and the aperture act as the valves for adjusting the quantity of light. As the term "shutter speed" suggests, it measures how long the "door" remains open for light to enter. Meanwhile, "aperture" can be understood as an indication of how wide the "door" is open. The amount of incident light can therefore be adjusted by controlling the shutter speed and the aperture. Proper exposure is obtained through the mutual interaction between these two components. While the appropriate amount of brightness may be achieved by increasing the shutter speed to open up the aperture on one hand, or by slowing down the shutter speed to stop down the aperture on the other, the concept of "exposure" is exactly the same in both cases. If we use marathon as an example, regardless of whether a runner reaches the goal by running fast or slowly, the actual distance covered remains unchanged.

Relationship between Shutter Speed & Aperture

The chart above shows the relationship between the aperture value and the shutter speed. For example, the same amount of brightness can be obtained in a photo either by opening up the aperture to increase the shutter speed or by stopping down the aperture to slow down the shutter speed.

Understanding What Proper Exposure Means


Proper Exposure


Brightness is pleasant to the eyes

"Proper exposure" refers to the correct level of brightness in a photo that appears pleasant to the eyes of the viewer. This definition is relatively vague, and depends largely on what the photographer believes to be the right level of brightness. However, there are cases where exposure would naturally fall within, unless the photographer brightens (or darkens) the image intentionally. If the brightness deviates considerably from this range, the resulting image would turn out either overexposed (too bright) or underexposed (too dark). Even when the brightness falls within the range of proper exposure, there are cases where a part of the image may appear extremely bright or dark. When the highlights are completely lost, ‘blowout' occurs. Meanwhile, an area that appears pitch black is referred to as ‘black crush'. These phenomena are more likely to occur when the overall exposure of an image is too far off the appropriate range, so it is important to maintain proper exposure at all times when you are taking a shot. Proceed to employ expression techniques to intentionally brighten (high key) or darken (low key) the image after you have grasped the concept of proper exposure.

Example of Blowout

The strong sunlight is reflected from the white tent, causing blowout to occur. To avoid this, decrease the exposure level.

Example of Black Crush

The high contrast causes the shadow areas to appear crushed. In this case, increasing the exposure may result in blowout in other areas instead.

Ryosuke Takahashi

Born in Aichi in 1960, Takahashi started his freelance career in 1987 after working with an advertising photo studio and a publishing house. Photographing for major magazines, he has travelled to many parts of the world from his bases in Japan and China. Takahashi is a member of the Japan Professional Photographers Society (JPS).