Camera shutters are like eyelids. They open for certain amounts of time and they stay closed for certain amounts of time. When a camera is off or not in use, the shutter stays closed by default. When someone presses the shutter button on the camera though, the shutter opens for a very specified length of time and then closes again. Just like when you open your eyes and your eyeballs and brain register what they see, a camera’s sensor registers what it sees when the shutter moves out of the way for that to be enabled.
If you aren’t aware, a camera’s sensor is the device that “sees” the scene and then captures that scene to be processed by the rest of the camera’s internals. It’s the shutter that stands in the way of the sensor. It’s not until someone presses the shutter button that the shutter moves for just long enough to give the sensor exposure to the scene. If you set your camera to open the shutter for a very short period of time, you’ll have a clear, crisp resulting image. It may be dark though because not a lot of light was let through during that very short period. Conversely, if you set your camera so the shutter stays open for a longer period of time, your photo may not be crisp at all if there was movement of the camera or something in the scene. Also, the shot may be overexposed due to the extended time the shutter was revealing the scene.
There’s actually quite a bit that goes into shutter speed. I’ve written a lot about this topic here, so I invite you to click through a few posts to learn about about this area of photography. If you have any questions, please be sure to ask down below.
What is Shutter Speed? How Does it Work?
Photography Basics: Shutter Speed, Aperture & ISO
What’s the Slowest Shutter Speed For Handheld Photography?
How To Work Camera Shutter Speed For Incredible Photos
Shutter Priority: How to Take Smooth Water Photos