减光镜也叫密度镜、灰镜。是众多滤色镜家族成员中的一个分类。形状有方片和圆片之分。按减光效果有浅密度、中密度和高密度之分。一般用编号ND2为浅密度 减光镜;ND4为中密度减光镜;ND8为高密度减光镜。

The light reducer is also called a density mirror and a grey mirror. It is a classification of many family members of color filters. The shape of a square piece and a round piece. According to the light reduction effect, there are shallow density, medium density and high density. In general, ND2 is used as light density light reducing mirror; ND4 is medium density light reducing mirror; ND8 is high-density light reducing mirror.

更高密度的减光镜，一般很少用。加用ND2减光镜，可以减少一档曝光量，加用ND4则可以减少两档 曝光量加用ND8则可以减少四档曝光量。如果需要进一步减光，可以两片或者三片减光镜同时加用。也可以将偏振镜当减光镜用，只不过它的减光效果不如前者。使用减光镜有三个问题值得注意：

High density light reduction mirrors are rarely used. The addition of the ND2 dimmer can reduce the exposure of a single exposure. If you add ND4, you can reduce the exposure of two files and add ND8, which can reduce the exposure of four files. If further dimming is needed, two or three lenses should be added at the same time. The polarizer can also be used as a light reducing mirror, but its light reduction effect is inferior to that of the former. There are three problems to be noted with the use of light reducing mirrors.

1、加用两片以上减光镜时，最好使用同一品牌的减光镜，因为不同品牌的减光镜的叠加会造成后期难以矫正的色彩偏差(黑白摄影可以忽略不计)。

1, when adding more than two pieces of light reducing mirrors, it is best to use the same brand of light reducer, because the superimposition of different brands of light reducer will cause the later difficult to correct the color deviation (black and white photography can be ignored).

2、选购减光镜时尽量购买质量好的。至少不能差于你的UV镜的质量。因为每一片减光镜都直接影响到照片的成像质量。

2. When you choose to buy a light reducer, try to buy a good quality. At least it can't be less than the quality of your UV mirror. Because every light reducing mirror directly affects the image quality of the photograph.

3、使用方片时，要注意防止晕光进入镜头，尤其是在使用两片以上方片减光镜时，这个问题似乎是无法避免。

3, when using the film, we should pay attention to prevent the lens from entering the lens, especially when using more than two lenses.