How Surface Finish Defines Optical Filter Lifespan and Efficiency
2025-03-10 11:26:54
The surface finish of the filter is a parameter that describes the maximum allowable size and quantity (number) of surface defects on the effective light-passing area of optical parts. It is the microscopic quality of the light-transmitting surface of the optical filter. It can essentially reflect the quality or cleanliness of the lens surface, indicating whether there are defects or spots on the surface that exceed the standard. The surface finish is usually expressed in numerical values. Understanding relevant indicators is crucial to selecting filters that provide the best performance.
Scratch-Dig Specifications
Scratch-Dig Specifications is governed by MIL-PRF-13830B, this standard limits the number of allowable defects per unit area. A 60-40 specification permits scratches≤60µm and spots≤40µm. Common Scratch-Dig Specifications in the market include 60-40/40-20, etc.
Take 60-40 as an example: 60 denotes the maximum scratch width in microns. -Scratches (Width ≤60µm): Measured as "digs," these narrow, elongated defects scatter light, reducing transmittance. 40 denotes the largest spot size in microns. -Spots (Diameter ≤40µm): Called "digs," these localized imperfections are capped at 40µm within any 20mm inspection area. Cumulative defect diameters in that area must not exceed twice the largest spot size.
Surface Roughness (Ra):
Measured in nanometers (nm), Ra values (e.g., <1nm) indicate average surface smoothness. Lower Ra minimizes scattering and maximizes transmittance. Why These Parameters Matter?
Scattering Control: A 60-40 filter reduces stray light by 30% compared to lower-grade finishes, crucial for laser systems.
Spectral Fidelity: Sub-20µm defects prevent wavelength distortion in hyperspectral imaging.
Lifespan: Filters meeting MIL-PRF-13830B withstand 10,000+ hours in harsh environments without degradation.
KS Glass has over 20 years of experience in customizing optical filters for high-end equipment and instruments. We can customize parameters in specific bands such as UV/IR/visible light. Choose Konshen Glass for filters where every micron is mastered. Contact us to request a surface finish analysis.
