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Focus variation
Focus variation is a method used to sharpen images and to measure surface irregularities by means of optics with limited depth of field.
The algorithm works as follows:
Focus variation requires an optics with very little depth of field. This can be realized if a microscopy like optics and a microscope objective is used. These objectives have a high numerical aperture which gives a small depth of field.
The use of this method is for optical surface metrology and coordinate-measuring machine. This means measuring form, waviness and roughness on samples.
With optimized hardware and software components a lateral resolution of 500 nm (limitation of wavelength of light) and a vertical resolution of several nm can be reached.
Advantages:
Disadvantages:
The ISO committee is working on a new series of ISO standards, called the ISO 25178 series. The 6-part document describes the available methods for roughness measurement. Focus variation is one of the described methods.
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Focus variation
Focus variation is a method used to sharpen images and to measure surface irregularities by means of optics with limited depth of field.
The algorithm works as follows:
Focus variation requires an optics with very little depth of field. This can be realized if a microscopy like optics and a microscope objective is used. These objectives have a high numerical aperture which gives a small depth of field.
The use of this method is for optical surface metrology and coordinate-measuring machine. This means measuring form, waviness and roughness on samples.
With optimized hardware and software components a lateral resolution of 500 nm (limitation of wavelength of light) and a vertical resolution of several nm can be reached.
Advantages:
Disadvantages:
The ISO committee is working on a new series of ISO standards, called the ISO 25178 series. The 6-part document describes the available methods for roughness measurement. Focus variation is one of the described methods.