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Light is one of life's most necessary elements. It gives plants energy, our earth warmth, and helps our eyes to see color and shape. For these reasons and more, light is very important for cameras. If it is controlled right, the sensor can easily define shape and capture a clean image which can help you make a video that can impress those around you.
Controlling light in a camera starts with controlling exposure. Exposure refers to the length of time that a camera's imaging device gets hit by light. Here's how it works. First, light passes through the lens of the camera stopping at the diaphragm or iris. The iris, which acts much like the iris in our eyes, opens slightly to let in less light or wider to let in more light depending on the strength of the light coming into the camera. Once it passes through the iris, it must pass through the shutter gate in some cameras. The shutter gate covers a sensor for a determined length then opens to let light in. Lastly, light reaches a sensor where the photons that make up light are captured, collected, converted into electrons and read by a computer. The more electrons in each pixel, the brighter that pixel will be during playback. The resulting ones and zeroes then get written to a recording medium and read on a computer during editing or playback.
One of the most used methods of controlling light is by setting a camera's aperture. The aperture controls two main functions: the amount of light that hits the camera and the depth of field
The iris or diaphragm on a camera is a multi-bladed opening that controls how much light hits the sensor. Much like your eye, the wider the iris, the brighter the image gets. Aperture is measured in f - or focal stops. Each stop down represents half of the light that was previously entering through the lens. The tricky part to remember is that the higher the f-stop number, the smaller the opening. As such, f22 on a camcorder usually blocks the most light while f1.8 usually means the iris is wide open.
Due to the way optics work, the wider the iris opening, the shallower the depth of field is in an image. Depth of field refers to how much of an image your lens can focus on at one time. If your lens can focus both near and far at the same time, you have a deep depth of field. If only near or only far, it has a shallow depth of field. Since an out of focus background can help you to draw focus on your subject, a shallow depth of field is usually desired. Opening your iris to its widest setting, usually f/1.8, will allow you to get the most shallow depth of field and draw focus to certain areas of your image.
When controlling light, it is also helpful to know the functions of a camcorder's shutter. The shutter is a window that sits in front of the sensor in a camcorder. This window opens for a short period of time to cut down the amount of light that hits the sensor and to lessen motion blur.
The simplest use for the shutter is to cut down on the amount of light that hits the sensor. By keeping the shutter gate open for only a short period of time, a sensor can gather very little light, making the image look darker. This can work well when in a bright outdoor environment. However, in a darker indoor environment, shutter speed is usually set to its minimum
The most common use for shutter speed is to either create more or less motion blur in an image. Motion blur is when an object moves across the frame during the time a shutter is open. This results in streaks where the the object was in the frame. Motion blur can be eliminated by opening the shutter for very short periods of time - either 1/2000th of a second or shorter - in order to cut down on the distance the object can travel in the frame before the shutter closes again. A fast shutter speed is often used in sports videography as it leads to better definition during slow motion replays.
The last method of controlling light in a camcorder is by using a built in neutral density filter. Neutral density filters are pieces of shaded glass that are placed in front of the lens in order to cut down the intensity of the light entering the camera. These filters act like sunglasses for a camera. They are usually located at the front of a camera as a switch that can select between three different filters. These filters are usually measured by how much light they cut from the camera in f-stops.
The aperture, shutter speed, and neutral density filters in your camera are great tools for helping you to control how light reaches your camera's sensor. Knowing how each one works and how to use them in concert with each other can take some time. However, that knowledge will result in beautiful images that can be captured under any lighting condition.