光学镀膜，影响一面平面透镜的透光度有许多成因。镜面的粗糙度会造成入射光的漫射，降低镜片的透光率。此外材质的吸旋光性，也会造成某些入射光源的其中部分频率消散的特别严重。例如会吸收红色光的材质看起来就呈现绿色。不过这些加工不良的因素都可以尽可能地去除。

Optical coatings have many causes that affect the transparency of a planar lens. The roughness of the mirror causes diffused incident light and reduces the transmittance of the lens. In addition, the material's absorbance, which also causes some of the incident light sources to dissipate, is particularly severe. For example, a material that absorbs red light will appear green. However, these poorly processed factors can be removed as much as possible.