What's the difference between a subtractor and a polarizer?

The difference between subtractor and polarizer is as follows:

1, the reducing mirror is also called medium gray density mirror, neutral grey mirror or grey mirror and nd mirror for short, and its main function is to reduce the amount of light entering the camera.

2. Polarizer, also called polarizer, referred to as PL mirror, is a kind of color filter. The achromatic function of polarizer is to selectively let the light that vibrates in a certain direction pass through, and it is often used to eliminate or weaken the strong reflection of non-metallic surface in color and black-and-white photography, thus eliminating or reducing the light spot. For example, in landscape and scenery photography, it is often used to show the texture of objects with strong reflection, highlight the scenery behind the glass, darken the sky and show blue sky and white clouds.

The polarizer consists of two pieces of optical glass with a tiny polarizing crystal (such as mica) with directional function sandwiched between them. There is also a manufacturing method. The interlayer between two pieces of optical glass is coated with crystals, such as polyethylene film or poly (vinyl cyanide). This polymer coating can produce a very fine fence-like structure, allowing only light in the same direction as the vibration of the gap to pass through. Then two pieces of glass are independently installed in a rotatable ring, and the polarized reflected light on the surface of the object can be eliminated by rotating one of the lenses. This coating will gradually age and fail, and its service life will be shortened due to humidity, impact and vibration.

References:

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