The Almighty Principle of Exposure

Exposure is the term for the amount of light that passes through the lens of a camera. And this exposure is determined by three main components, which are:

1. ISO or Gain: This is a number representing how sensitive the sensor is to light; the higher the number, the more sensitive the sensor.

2. Frame rate and shutter speed: Frame rate describes how many images are displayed per second whereas shutter speed stands for the amount of time that every image is exposed to light. Since both go in conjunction, shutter speed directly affects how much motion blur you will have on your frame. If you want a clear image, the number of the shutter speed should be double the number of frames. Also, the higher the number of the shutter speed, the sharper (but also more artificial) the image becomes. European standards for frame rate and shutter speed should be 24 or 25fps and 1/48 or 1/50, whereas the American standard is located at 30fps and 1/60. Increasing the framerate to 50 or 60fps (and the corresponding shutter speed to 1/100 or 1/120 allows to be used for slow motion, whereas anything above 16fps (as the very first short films were recorded in) already looks like motion to our eye. Looking at this plethora of information, it becomes apparent that the very first question you should always ask before filming is the question of where and how the film is going to be displayed, since that not only defines the resolution of the material and the question of interlaced or progressive image transmission, but also defines the frame rate.

3. Iris or f.: Controls how much light can physically enter the lens; the more it closes in on itself, the less light comes in, the more shallow the depth of field becomes

In short, this means that:

1. the ISO controls the pictures quality,

2. the shutter speed the motion blur or sharpness,

3. and the iris the depth of field.

These factors are all interacting and interfering with each other, as you can see on the chart below:

But wait! There’s more. The focal length also controls the depth of field! And staying at the matter of focal length for a brief moment, I learned another lesson which I never thought before: If you zoom fully out on your lens, the wall (or any straight line for that matter) starts warping, thereby distorting the image. I have a couple of these images at home that, while portraying a nice effect as they are, were not really meant to be that way. Also, there are neutral density (or nd-)filters that can further reduce the amount of light entering the lens.

One further thing to regard is the light temperature, measured in Kelvin: Light can have a variety of colour temperatures, of which the extremes are tungsten lighting and daylight. While daylight lies at approx 5500k, the red tungsten light takes over at 3300k. Candlelight, for example, is located at about 2600k whereas sunsets are in the middle between tungsten and daylight. Since the colour temperature has great influence on the way colours are recorded and a camera lens is not as proficient as the human eye in detecting what white looks like in every light setting, you always have to tell the camera by white-balancing it against a white surface that covers at least 80% of the frame and hit AWB on your camera. Since the light setting outside changes constantly due to changes in the atmosphere and the sun moving, you constantly need to white-balance.

Reference:

Techradar (2017) The Exposure Triangle: aperture shutter speed and ISO explained [online] http://bit.ly/2jtKYpE [Accessed 10 October 2017]​MerkenMerkenMerkenMerkenMerkenMerkenMerkenMerkenMerken