Exposure (photography)

Exposure is how much light reaches a camera's film or digital sensor.

This light creates the picture we see. Three main things decide the exposure level. First is the scene luminance, which is the brightness of the scene. Second is the lens f-number, which tells us how wide the lens opens. Third is the exposure time.

This is how long the shutter stays open to let light in. Photographers can use a long exposure to gather dim light. This can make moving water look blurry in a single shot.

To get a good picture, you must control the light carefully. If there is too much light, the photo is overexposed. This can cause blown-out highlights, where bright parts look completely white.

If there is too little light, the photo is underexposed. This leads to blocked-up shadows, where dark areas look muddy or black. A photographer might do this on purpose for art. They might want a white cloth to look very clean. They might also want heavy, dark shadows for a specific mood.

Cameras have different ways to manage these light settings. In automatic exposure mode, the camera calculates the settings for you. It uses a tool called an exposure meter to guess the best light. Most cameras use a system called TTL to do this.

You can also use aperture priority or shutter priority modes. These modes let you choose one setting while the camera handles the other. In manual mode, you control everything yourself. This gives you the most power to reach your goal. Some people use the Zone System to help plan their shots.

There are specific rules for finding the right balance. One helpful guide is the sunny 16 rule. On a sunny day, you might use an aperture of f/16. You would also use a shutter speed related to your film speed.

This rule helps you find a starting point. You can also use exposure compensation to fix mistakes. If you set it to +1, you get twice as much light. If you set it to -1, you get half as much light. This is very useful when the camera's meter makes a wrong guess.

Understanding exposure helps you connect different parts of photography. You can use reciprocity to balance your settings. If you keep the exposure the same, you can trade speed for aperture.

For example, a longer shutter speed needs a smaller lens opening. This allows you to change the depth of field in your image. You can also use multiple exposures to create a single image. This is called a multiple exposure. Some people even combine many shots to make an HDRI image. This helps capture both very bright and very dark details at once.