Angle of incidence (AOI) refers to the tilt of an optical filter with respect to the incident light (Figures 1a-1c). Figures 1a-1c: Diagrams showing (a) normal AOI for an optical filter, (b) 45° AOI for a dichroic. By Daniel Obeid When integrating an optical filter into the design of an optical system, it is vital to understand the angle of incidence (AOI) and cone half angle (CHA) requirements on the filters to optimize functionality for a wide variety of life sciences and biomedical research applications. However, at larger angles, significant deviations from the expected spectral response are observed, particularly. First of all, it's important to make clear that this analysis applies specifically to filters that operate by optical interference effects, which in practice most “precision” optical filters do. As you adjust this angle, especially outside the filter's.