All About Optical Systems and Lens Technologies

What is optical lens coating?










1. Why do optical lenses need to be coated?

Even if you try to pass 100% of the light through the lens, 100% of the light will never pass through.


2. The reason why light does not pass through the lens 100% is because it is reflected on the surface of the lens or within the lens, causing light loss.

3. So what is the actual reflectance? Let’s do some calculations.

*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.


4. How can I increase the amount of transmission?

That’s why we coat the optical lenses to increase the amount of transmission.

Let me explain the details below.


5. What kind of coating reduces reflectance to zero?

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.



6. Let’s calculate the transmittance when the actual single-layer coating is applied.

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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