How to calculate the OD value after overlaying the filter

Recently, some customers have inquired about the conversion of OD values after stacking filters. Today, we will explain in detail:

Firstly, there are two types of filters:

The finished product obtained by coating with chemical components through photo controlled high-temperature evaporation or magnetron sputtering is called a dielectric filter (also known as an interference filter), which belongs to the reflective type of filter.

2. Colored glass filters are absorption type filters that utilize substances (usually heavy metals) doped in glass to specifically absorb light in specific wavelength bands.

The OD value of both types of filters refers to optical density, which mainly represents the degree of cutoff of the filter and is closely related to the amount of energy transmitted through it. In addition to optical density, there are many optical parameters in the filter, such as peak transmittance, center wavelength, bandwidth, cutoff range, and so on.

OD refers to the partial absorption or reflection of light when it passes through a sample, and in spectroscopy, transmittance is the ratio of the intensity of the outgoing light to that of the incident light.

Two reflective filters stacked together can achieve a specific OD value, OD=lg(10OD1+10OD2-1), For example, the OD value of a reflective filter with OD1 and OD2 stacked together is 2.307, and the transmittance is 0.493%

After stacking two absorption type filters, a specific OD value will also be reached, OD=OD1+OD2， For example, the OD value of an absorption filter with OD1 and OD2 stacked together is 1+2=3, and the transmittance is 0.1%