Color filter is widely used in photography creation, printing plate making and various scientific and technological photography. Color filter is divided into red, green and blue primary color filters and yellow, magenta and cyan complementary color filters. In map re-photography, color filter is used to separate the multi-color original image. According to the type, it can be divided into four types: colloid, glass, glass and colloid synthesis, glass and liquid synthesis. Generally, red, yellow, blue, purple and other colors are used as a set. Commonly used ones include protective filters, compensation filters, color separation filters and interference filters.

Filters are auxiliary components of microscopes. Reasonable selection can improve the image quality. Filters have the following main functions:

1. Use yellow-green filters with achromatic objectives to correct aberrations.

2. For apochromatic objectives, blue filters can be used; since the wavelength of blue light is shorter than that of yellow-green light, the resolution of the objective can be improved.

3. Reduce the intensity of the light source. In addition to the commonly used yellow-green filters, the new microscope also has one or more gray neutral density filters, which can be used to reduce the intensity of the incident light without changing other characteristics of the incident light. This kind of filter is preferably made of alloy to form an evaporation precipitation film on the glass, and can be made into filters with different light transmittances according to needs, and its transmittance can range from 80% to 0.001%.