Optical Performance Standards for Filters
So far, we have discussed directly measuring the optical properties of filters, but there are still some natural properties of objects that are difficult to measure, which are related to the quality and processing of the film and substrate. For any optical component, a detailed description of the substrate will be provided, such as surface shape, polishing degree, allowable smear, smoothness, etc. The substrate should not be considered here. Mil-e13830a has been widely used in the United States, providing an effective standard for optical components including substrates.
The quality of the coating can be measured by the presence of defects such as pinholes, stains, sputtering marks, and uncoated areas. There are two main reasons for pinholes.
Firstly, they actually have very small uncoated areas or some uncoated areas, which will result in additional light transmission cutoff areas, thereby reducing the overall performance of the filter.
Secondly, for visible light filters, these drawbacks will affect the overall appearance. In fact, they make the appearance look worse than the actual performance. In addition to simple appearance judgment, the allowable size of pinholes can also be determined based on the maximum value per unit area of a given size, that is, the number of pinholes when the cutoff value of the filter decreases to the given value.
To calculate this value, it is necessary to assume the minimum area of the filter used at any time. It is obvious that the smaller the area, the smaller the number of pinholes. Of course, the actual calculation of pinholes in any filter requires a significant amount of manpower. In practical applications, when comparing the filter with a reference sample, the measurement of the visible filter is often visualized.
A simple lightbox mounting bracket can be easily constructed and a large number of filters can be placed on it, which can be compared with reference samples to determine if it meets the requirements. For filters on opaque substrates, it is easier to measure their actual cutoff performance.
Generally speaking, unless the quantity is large, the impact on optical performance is minimal. An important risk is that material fragments may fall off and pinholes may appear. The sputtering process can sometimes cause the growth of nodules and bring some problems, or if there are a large number of sputtering fragments, scattering losses may increase. Like controlling pinholes, this can be controlled, but due to the fact that the optical performance of specular reflection is almost unaffected, the determination of allowable values is often subjective unless the number of sputtered marks is large. If pinholes are generated by sputtering, they will be processed separately.
Generally, it is stated in the indicators that there are no visible sputtering trajectories, but this description is very vague, especially when the inspector has no optical experience. When the user inspector uses a lens to assist visual observation, there may be differences between the user and the manufacturer. When it is possible to use the same precise method as the test pin hole, it is best to link the test with the reference sample agreed upon by both parties.
The quality of the coating can be measured by the presence of defects such as pinholes, stains, sputtering marks, and uncoated areas. There are two main reasons for pinholes.
Firstly, they actually have very small uncoated areas or some uncoated areas, which will result in additional light transmission cutoff areas, thereby reducing the overall performance of the filter.
Secondly, for visible light filters, these drawbacks will affect the overall appearance. In fact, they make the appearance look worse than the actual performance. In addition to simple appearance judgment, the allowable size of pinholes can also be determined based on the maximum value per unit area of a given size, that is, the number of pinholes when the cutoff value of the filter decreases to the given value.
To calculate this value, it is necessary to assume the minimum area of the filter used at any time. It is obvious that the smaller the area, the smaller the number of pinholes. Of course, the actual calculation of pinholes in any filter requires a significant amount of manpower. In practical applications, when comparing the filter with a reference sample, the measurement of the visible filter is often visualized.
A simple lightbox mounting bracket can be easily constructed and a large number of filters can be placed on it, which can be compared with reference samples to determine if it meets the requirements. For filters on opaque substrates, it is easier to measure their actual cutoff performance.
Generally speaking, unless the quantity is large, the impact on optical performance is minimal. An important risk is that material fragments may fall off and pinholes may appear. The sputtering process can sometimes cause the growth of nodules and bring some problems, or if there are a large number of sputtering fragments, scattering losses may increase. Like controlling pinholes, this can be controlled, but due to the fact that the optical performance of specular reflection is almost unaffected, the determination of allowable values is often subjective unless the number of sputtered marks is large. If pinholes are generated by sputtering, they will be processed separately.
Generally, it is stated in the indicators that there are no visible sputtering trajectories, but this description is very vague, especially when the inspector has no optical experience. When the user inspector uses a lens to assist visual observation, there may be differences between the user and the manufacturer. When it is possible to use the same precise method as the test pin hole, it is best to link the test with the reference sample agreed upon by both parties.