How do filters work?
When a beam of white light passes through a coloured filter, its distribution of wavelengths changes. The coloured filter is made of a material which can absorb certain ranges of wavelengths within a distribution of light, and transmit others. In the case of a red coloured filter, the filter transmits a light beam with not many short wavelengths, some middle wavelengths and many long wavelengths.
Figure 1. Visualization showing the relative amounts of a light beam’s short, middle and long wavelengths transmitted by a red filter.
Each coloured filter (in the Colour Paddle set or otherwise) transmits light with its characteristic set of wavelengths. Figure 2 shows a photo taken with no filter, and a photo of the same scene taken by placing a red filter in front of the camera.
Figure 3. Graphs of the amount of light transmitted by each filter (on y-axis) vs. wavelength (on x-axis).
The back of the filter paddle set shows a graph of how much light is transmitted by each filter vs. wavelength. This type of graph is called a transmission curve. The transmission curves for the filter paddle set are shown in Figure 3. In the top left of Figure 3, we see how the red filter absorbs light with short and middle wavelengths, and only transmits a range of long wavelengths.
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