What is Cone half angle (CHA)?
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CHA, sometimes called HCA (Half-Cone Angle), means the light entering the filter is divergent or convergent rather than perfectly collimated.
CHA is the angle between the main direction of the light beam (usually the AOI direction) and the outermost rays. It describes how much the light beam spreads out.
When CHA increases, the filter’s transmission performance gradually worsens, showing:
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The peak transmission wavelength shifts to shorter wavelengths (blue shift);
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The overall transmission decreases;
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The spectral peak shape becomes distorted.
