Introduction to Filter Function
A filter lens, as the name suggests, is an optical component that filters out a portion of light. Due to the fact that the characteristics of light are determined by two factors, frequency and intensity, filters are divided into two categories: frequency filters and intensity filters. Among them, frequency filters are also known as filters, because the color of light is caused by its different frequencies. Intensity filters include skylight filters, and frequency filters (color filters) include orange filters, yellow filters, etc. Filters of different colors can play different roles.
The function of a filter
1. Expressing Cloud Sky
Most outdoor photography activities cannot do without the representation of the sky. Blue sky, white clouds, or brilliant clouds can often make ordinary windscreens appear colorful and radiant, even in daily photography, white clouds and blue sky are a pleasant background.
To display blue sky and white clouds, a yellow filter can be added. It absorbs light from the blue sky and white clouds, but for the blue of the blue sky, purple light absorbs more, so it presents a dark gray tone, while white clouds absorb less light. In this way, white clouds are more prominent in the dark gray sky.
If you use orange and red filters to display the sky, although it can make the blue sky darker and the white clouds more prominent, it often gives people an unnatural distortion. Therefore, generally speaking, it is not suitable to use red and orange filters to depict blue sky and white clouds unless a special artistic effect can be created.
2. Correct color light
Sometimes black and white film is used to shoot under lighting conditions because there is too much red, yellow, and orange light, and too little blue and purple light. A blue filter can be added when needed to absorb too much red and orange light, in order to relatively compensate for the shortcomings of blue and purple light. When shooting red flowers and green leaves, adding a red filter will make the flowers bright and the leaves dark; Adding a green filter will darken the flowers and brighten the leaves. In color photography, in order to achieve color balance of various colors in the scene on color sensitive film, filters that can adjust colors are usually selected to correct color light.
3. Eliminate dust and mist
When the blue and purple light from the sun passes through these dust clouds, it will scatter in large quantities, making the distant scene appear blurry and hazy. The farther the distance, the greater the blurriness. If shooting distant scenes in this situation, the image will not be particularly clear because the photosensitive film is very sensitive to the blue and purple light diffused by dust and fog.
At this point, we need to choose some filters that can absorb and attenuate blue purple light. In general, darker yellow, orange, or red filters can absorb the scattered blue and purple light from dust mist, allowing distant objects to be clearly reflected.
4. Remove color
When shooting colored objects, if you need to eliminate or reduce one color, you can choose the same color filter. This color is filtered extensively and appears as white in the photo. For example, when taking photos of objects contaminated with a certain color, simply adding a filter that matches the contaminated color can eliminate the color and achieve satisfactory results.
5. Adjust contrast
Due to the different sensitivities of the film to various colors in the spectrum, the colors of the scene are different, and the grayscale characteristics reflected in the exposed image are also different, mainly manifested as insufficient or excessive contrast. In order to adjust the color of a certain part of the scene and enhance or reduce the reflected tone in the photo, it is necessary to choose appropriate filters to increase or decrease the amount of light passing through this part of the color.
When shooting snow scenes with blue skies and green trees in winter, the contrast between white snow, blue sky, and green trees is very high. If a light green filter is used, a relatively harmonious contrast effect can be obtained; When shooting objects with red characters on a yellow background, only green filters can be used with yellow lighting to make the yellow background bright, the red characters black, and the handwriting more prominent. On the contrary, if red and yellow light can pass through orange and red filters, it will weaken the contrast, making the yellow and red colors appear light gray and the handwriting less obvious; In order to adjust the contrast between the brightness of a character's face and the brightness of the sky, a yellow filter is usually used to obtain a normal color tone.
6. Special effects
Adding a dark red filter in strong outdoor sunlight can achieve the effect of a moonlit night; If a dark red filter is combined with a polarizer, it can further enhance the atmosphere of the night scene. This method is commonly used to create outdoor night scenes when shooting external scenes in movies.
7. Reduce brightness
In some excessively bright environments, such as seaside, snowy areas, etc., although the exposure combination has reached its limit, it still cannot achieve moderate exposure. At this point, in order to adapt the brightness of the scene to the exposure combination, it is necessary to choose a neutral grayscale filter that can reduce the brightness of the scene, thereby reducing the brightness of the scene generally and achieving the required brightness for exposure.