Neutral gray is also called the gray density mirror, ND mirror for short, is a senior grey pure transparent optical glass.Its role is by weakening the amount of light through the lens to reduce exposure.This kind of filter function is optional, that is to say, ND mirror's ability to reduce all kinds of different wavelengths of light is equal, even, only have the effect of less light, and the color of the original object won't have any effect, so can truly represent the contrast of scenery, color photography and black and white photography.According to "stop" light ability strong and the weak, the density of neutral gray mirror has a variety of options, such as ND2, ND4, ND8 (respectively extend "1, 2 and 3 shift the shutter speed), can also be more neutral gray lens combination.It is not hard to see, ND behind the Numbers, which represents the ND mirror ability to block the light.ND value, the greater the partial color is more serious, general and high grade products are using other technologies to wavelength, as far as possible to colour the smallest distortion and the reduction of most loyal.

ND mirror just reduce the intensity of the light, so it will not affect the final image color, also won't affect the camera's white balance and automatic exposure.Using a ND mirror, not to be any impact on the color of the object and contrast.In addition, due to the SLR is through the lens of metering, so ND mirror will not affect the camera's automatic exposure system to produce any.

All in all, the need for human to use the slow shutter, or reduce the external light cases, additional lens ND mirror is very practical., of course, due to the different lens aperture is different, so the ND mirror also has different caliber, when use should be according to the diameter of the lens to choose different caliber ND mirror.