Types and Uses of Traditional Optical Filters

Ⅰ. What are optical filters?


The color filter is a colored transparent sheet that absorbs, reflects and transmits colored light. The optical filter is made of colored optical glass material, which has undergone optical processing and surface vacuum coating. It has specific spectral characteristics.


Ⅱ. The use of optical filters


In black and white photography: the optical filter glass can play the three functions of passing, restricting and preventing various colored lights. If the amount of colored light passes through, the color tone on the photo is light; if the amount of light passed is small, the color tone is darker. If it is completely prevented, the color tones are all black, so the color mirror in black and white photography actually corrects the level of the object color contrast, so that the colors of various objects become in line with the requirements of their own contrast and ideal tone. 


In color photography: change the color tone, correct the color temperature and special effects.


Ⅲ. Classification and use of optical filters


1. What is the classification method of optical filters?


1) According to purpose:


① Color filter: adjust various colors in the spectrum.


② Polarizer: Eliminate the glare and reflection formed by light on the surface of the object.


③Diffuser: soften the light.


③Special effect mirror: starlight, multi-shadow, medium gray, UV, infrared, etc.


2) According to materials:


① Color film filter: high transparency, many colors, low cost, but easy to damage and easy to fade.


②Glass laminated color filter: high transparency and many pigment levels, but the increase in thickness will change the focus and affect the clarity.


③Colored glass filter: high transparency, thin texture, will not change the focus of the lens, and resist moisture and heat. But the pigment grade is slightly worse.


④Liquid color filter: Pour colored liquid into a transparent container, change the color as you like, and place it in front of the lens, which is mostly used for scientific photography.


3) By color:


①Weak color filters: such as No. 0 light yellow and No. 1 light yellow filters;


②Neutral color filters: such as No. 2, No. 3 yellow and No. 1 orange, yellow-green and light green color filters. It is indispensable when shooting scenery, flowers, bonsai, and still life;


③Strong color filters: such as No. 2, 3 orange, No. 4 yellow, deep red and No. 2 red color filters. Taking landscape photos can eliminate the haze in the air perspective, making the distant view exceptionally clear.


4) Special category:


①Ultraviolet filter (UV mirror);


② Polarizing filter;


③Infrared color filter;


④ Fog mirror;


⑤ ND filter;


⑥Film-changeable color filter.


2. What are the functions of various optical filters?


①Weak color filter: It can only absorb ultraviolet light and a small amount of blue-violet light, and all other colors can pass through, with low absorption and high pass rate. Compared with the hue of the subject, there is no obvious difference between the tones of the photos taken (except for the color separation film and the blind color film). The commonly used No. 0 yellowish and No. 1 yellowish filters are weak color filters. The use of this type of filter generally does not affect the exposure, and is mostly used when the illumination is weak or the subject is moving fast.


②Neutral color filter: It can absorb most of the blue-violet light, has a larger absorption power and a slightly lower pass rate. Compared with the tones of the photographed scene, the tones of the captured photos appear natural and moderate, achieving a more ideal effect. Generally, No. 2, 3 yellow and No. 1 orange, yellow-green and light green filters are neutral filters, which are commonly used in photography. When shooting scenery, flowers, snow scenes, buildings, outdoor portraits and still life, it is often inseparable from a neutral filter.


③Strong color filter: It can absorb all the blue-violet light, and can only pass the required part of the colored light. It has a great absorption power and a low pass rate. Compared with the hue of the shot scene, the tones of the photos taken have a strong contrast, and the adjustment of the scene color goes beyond the natural state. Normally, color filters with strong colors such as No. 2, 3 orange, No. 4 yellow, dark green, and No. 2 red are strong color filters. Using it to shoot distant scenery, it can eliminate the haze in the air perspective, making the distant view exceptionally clear. Optical filters are widely used in photography creation, printing plate making, color photography and magnification, and various technical photography.

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