Filters are an essential tool in photography and cinematography, used to selectively modify the wavelengths of the components of a mixture. They come in two types: screw filters and slot filters. Screw filters are circular and are screwed directly into the thread on the front of the lens, while slot filters are square or oblong in shape and mounted on a support accessory or, more commonly, on a glass or plastic disc within an annular metal or plastic frame. Filters can be used to minimize glare and reflections, improve colors, reduce light entry to the lens, and much more.
Each lens filter has a specific purpose, as each one is designed to offer a specific effect that can help improve the final look of an image. Color subtraction filters work by absorbing certain colors of light and letting the remaining colors pass through. However, you can use a color balance filter to compensate for the various differences in the color of the photographed light. Transparent filters, also known as window filters or optical flat lenses, are transparent and (ideally) do not filter incoming light.
A variable neutral density filter is a great option if you want to enjoy a variety of filtering options in a compact accessory. It also helps reduce haze and fog, but its effects on the sky and clouds are more subtle than those of the red filter. Additional foreground filters are designed for use with that specific lens and work perfectly with the focal length and internal elements of the lens to help you get physically closer to your subject without sacrificing sharpness. A deep green filter will also darken the sky and, in addition, lighten the green foliage so that it stands out against the sky. Close-up filters (also known as macro filters or diopters) allow you to take macro photos without having to use a specific macro lens.
Some camera ND filters are variable, so you can rotate them to block more or less light as needed. A graduated neutral density filter is a neutral density filter with different attenuation at different points. Normally, it is diffused in one half and is diffused with a higher density in the other. To mount the filters in a camera, the filter was placed between two rings: the mounting ring was screwed into the lens threads or slid over the lens body, and the retaining ring was screwed into the mounting ring to hold the filter in place. A neutral density filter (ND filter) is a uniform density filter that dims light of all colors equally.