Even if you try to pass 100% of the light through the lens, 100% of the light will never pass through.
*The glass incidence angle condition is vertical angle (90°).
3-1) Surface reflection only
What is the transmission rate of light through the glass?
Without the coating, the transmittance is approximately 91.58%.
3-2) When total system reflection is taken into account.
The transmittance is approximately 91.75%.
Comparing the calculation results of 3-1) and 3-2), there is an error of about 0.2%.
When calculating reflections in a simplified manner, 3-1) is generally used.
That’s why we coat the optical lenses to increase the amount of transmission.
Let me explain the details below.
Let’s consider a simple single-layer coat.
For the single layer coating, we used the following equation to calculate;
There are two conditions under which the reflection is zero.
In reality, when using a substrate (N=1.57), the refractive index for 0% reflection is 1.23, but there is no such film material, and MgF2, which is the closest and has the strongest film structure, is currently used.
Result Glass substrate 91.75% → 97.41
The transmittance was improved by 5.66%.
As you can see, when it is necessary to improve the transmittance, it is possible to improve the transmittance by coating.
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