Although, the performance required for the lens filter for camera and video largely depends on its usage,
* To deliver a necessary light beam to a film and a light receiving element, and
* to remove an unnecessary light beam before entrance into the lens
are fundamental performance.
Since a photograph and video are a tool to reproduce “a world seen by human eyes” (as long as it is not for a special use such as astrophotography), it is necessary to deliver a “wavelength of sensible light by human eyes, that is, visible light” to a film and a light receiving element.
The lower bound of visible light is approximately 360,400 nm (nanometer). The upper bound is approximately 760,800 nm.
For example, even if there is optically excellent glass that can transmit light having any wavelength, when the glass transmits light beyond a visual light range, that is, unnecessary light for a camera and a video, it cannot be said that the glass is an excellent product for a lens filter.
In order to control them, the surface of glass is subjected to evaporation coating by a special material to change characteristics of the lens filter.
The main purposes of coating are as follows:
* to increase transmission factor;
* to suppress reflectance;
* to cut ultraviolet rays by a particular wavelength;
* to change color tone; and
* to prevent stains.
A current main stream is “multi coating”, that is, a sheet of lens filter is subjected to these multiple coating.