Neutral density spectroscopic film is also known as attenuator, ND mirror. It identically and uniformly reduces light of different wavelengths, effectively reduces light, and does not change the color of the original object. Therefore, it can truly reproduce the original color of the object. It has the advantages of wide band attenuation rate, accurate attenuation, insensitivity to incident angle and polarization state, solid film layer, scratch resistance and strong hydrophobicity.