How “shutter speed” plays it’s role in exposure

With a DSLR the “shutter” is a mechanical mechanism. In a compact, bridge or phone camera the shutter is non-mechanical and is achieved by using an electronic method of reading the pixels of the sensor in groups of lines over a period of time. To simplify our discussion we will think of the shutter as a mechanism.

The “shutter” can be imagined as a curtain in front of the camera sensor. This curtain opens for a specific period of time allowing the light to reach the sensor and then closes to block the light from the sensor. The “duration” of time the light is contacting the sensor is referred to as the “shutter speed” and is what contributes to the exposure.

Mechanical Shutter

In the diagram step 1 shows the shutter in it’s normal closed state. When we push the “shutter button” on our camera the shutter opens, as shown in step 2, by the 1st curtain moving to the top and allowing the light to reach the sensor. Once the duration of the shutter speed has been reached the shutter closes, as shown in step 3. Finally the shutter mechanism resets to the normal closed state by the 1st and 2nd curtain moving together back to the bottom as shown back at step 1.

To recap we have learned in previous lessons that “aperture” is a hole in the lens which allows an amount of constant light into the camera based on the size of the hole we set. The “shutter speed” controls the “duration” of time the light is allowed to reach the sensor. The combination of these two settings, aperture and shutter speed in addition to the amplification (iso) of the sensor  determines the “exposure“, or the brightness of our captured image.

To find out how to set the shutter speed on your camera, refer to a previous lesson How to set your Camera’s; Aperture, Shutter Speed, and ISO.

Shutter Speed Typical Values

Shutter speed settings are in fractions of seconds to seconds in duration, which can be from 1/4000 (fast, less light), or 1/8000 on advanced cameras, of a second down to 30 (slow, more light) seconds in duration and depending on the mode you have selected you can control the this speed in full stops, typical values shown in bold, or 1/3 stop increments.

The shutter speed setting can affect sharpness and/or blur in your captured image, which we will discuss in our next lesson.

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