exposure-triangle

The exposure triangle works on the basis that changing one of the sides of the exposure triangle will have an impact on the other two. This means that you can never look at one as a singular thing, and have to always be conscious of them all.

Aperture

In the lens of a camera there is an opening that controls the amount of light reaching the digital sensor (or film). The ring around this is called the aperture and can be adjusted to allow more or less light to pass through, and the size of the opening is measured in f-stops. The higher an f-stop is, the smaller the aperture is opened up and so the less light is let in.

Aperture is used to alter the depth-of-field. Basically, if you want a shallow depth of field, it means objects in the foreground, close to the camera will be in focus, and all of the background will be out of focus. To achieve a shallow depth-of-field, you need the aperture wide open so it will be a low f-stop. Therefore, a small aperture will have the opposite effect, and give a wide depth-of-field, meaning the entire scene in your shot will be in focus.

aperture

Shutter Speed

There is a shutter in a camera that rolls over the digital light sensor, allowing light to hit the sensor for only a fraction of a second. The slower the shutter speed is, the longer the light is allowed to hit the sensor so the brighter the picture is. That’s how it works for stills, and it’s pretty simple, but with film it’s more complicated, because film is not just one still, it’s a whole series of them.

The longer the shutter exposes the sensor, the longer the light is hitting the sensor, so if the object is moving it will come out blurry. So in film, the faster the shutter speed is, the more individual movements it will capture, so the less blurry each still that makes up a film will be. To make it easier to understand, here are stills from rice being dropped with different shutter speeds. In order, the shutter speed goes: 1/30th of a second, 1/50th of a second (the one we will normally use), 1/100th of a second, and 1/200th of a second.

videoshutter_02

As you can see, a slower frame rate produces a blurrier video.

ISO

ISO is basically the sensitivity of the light sensor, it sets the amount of light that is needed for good exposure in a video. If you are filming in low light, you are going to need the sensitivity to be high so you can bring in as much light as possible, but if you’re filming in in bright light, you won’t need as much sensitivity. ISO also affects how much ‘noise’ there is in the image, meaning how grainy the image is. Normally, people like videos to look as clear and sharp as possible, so film makers try to avoid grainy imagery unless it is being used for a specific effect.

White Balance 

A camera does not work the same as a human eye. It cannot automatically pick out the different colours, a digital camera works in 1’s and 0’s and different types of light can sometimes fool the camera. For example, indoor lights can be quite orangy in colour and make the room slightly orange, but the camera doesn’t know this and picks up the colour in the room exactly as it is. White balance is where you pick out a part of your shot that is white, giving your camera a base so it can correct the rest of the colour, cancelling out any unnatural tones like the orange of an indoor light.

white balance

Frame Rate

A video is actually just a series of stills played in quick succession to trick the eye into believing it is a moving image, like an animation. FPS stands for frames per second and it is literally that; it measures how many stills were captured within one second. A high frame rate produces a smoother video, because there are more frames flashing past your eyes so it is impossible to distinguish between them. For low frame rates, the video appears choppy and jumpy, because your eyes have started to be able to notice the individual stills. The lowest frame rate you can get away with where the eye cannot notice the individual stills is 24 fps.

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One Response to

  1. kendalcollegefilm says:

    Outstanding technical summary—well done. Look forward to seeing you put this understanding into practice—this is an excellent base from which to work.

    Like

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