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According to Edmund Optics, the best anti-reflective coatings have R ≅ 0.4% = 0.004 over the visible spectrum (~400-700nm). R = 0.005 may be more realistic for a reasonable range of incident angles. The light reflected back to the sensor from each secondary reflection would be R2 = 0.000025 = 2.5*10-5 = -92 dB (20*log10(R2)). The number of secondary reflections Nsec increases rapidly with the number of components M (groups of elements cemented together, each of which has two air-to-glass surfaces) in a lens: 1 for one component; 6 for two components; 15 for three components; 28 for four components; 45 for five components, etc. For M components,
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M = 5 components are typical for high-quality camera phones; M ≥12 components is commonplace for DSLR zoom lenses. Overall, lens flare is less severe than the number of secondary reflections suggests because stray light does not cover the whole image; it decreases with distance from bright regions. It’s easy to see why practical camera DR measurements are limited to around 70-90dB, even when sensor DR is much higher.
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Because the ISO 18844 flare model does not measure the spatially dependent flare caused by lens reflections, it has limited value in characterizing practical system performance.
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