Filter size parameters and surface quality
Diameter tolerance
The influence of the filter diameter tolerance on the use process is not very big. The main consideration is that if the filter is installed on the equipment, the diameter tolerance should be considered.
Generally, the diameter tolerance of (± 0.1 mm) is called general precision, (± 0.05 mm) is called precision precision, and (± 0.01 mm) is called high precision.
If it is not limited by requirements, ± 0.1 mm can be used in mass industrial production. The more stringent the tolerance requirements are, the lower the yield will be, and the production cost (quotation) will also be higher.
Center thickness tolerance
The central thickness is the thickness of the central part of the filter (or other optical elements).
Generally, the tolerance of center thickness at (± 0.2mm) is called general precision, (± 0.05mm) is called precision precision, and (± 0.01mm) is called high precision.
If it is not limited by requirements, ± 0.1 mm can be used in mass industrial production. The more stringent the tolerance requirements are, the lower the yield will be, and the production cost (quotation) will also be higher.
The central thickness of an optical element (typically a lens) measures the material thickness of the central part of the optical element. The central thickness is measured by the mechanical axis of the lens, which is defined as the axis between the outer edges of the lens.
Filter surface quality
The quality of the filter surface is used to measure the surface characteristics of optical products, and covers some flaws such as scratches and pits. The commonly used specifications for surface quality in China are those for scratches and pits described by MIL-PRF-13830B. The names of pits are calculated by dividing the diameter of pits in micrometers by 10. Generally, the scratch pit specifications within the range of 80 to 50 are called standard quality; It is regarded as accurate quality within the range of 60 to 40; A range of 20 to 10 is considered high precision quality.
Filter surface flatness
Surface flatness is a kind of surface accuracy measurement. It is used to measure the deviation of mirrors, window pieces, prisms or flat mirrors. The deviation of smoothness is usually based on the ripple value（ λ) They are composed of test sources with multiple wavelengths, one stripe corresponds to 1/2 wavelength, and the smoothness is 1 λ， Represents the general quality level; Smoothness is λ/ 4, represents the precise quality level; Smoothness is λ/ 20 represents the quality level of high precision.
Surface flatness is a type of specification for measuring surface accuracy. It is used to measure the deviation of planes such as filter, reflector, window piece, prism or flat lens.
