Angle of Incidence, or AOI, is the angle at which a collimated beam of light is incident on the filter's first surface, measured relative to the surface normal. Cone half-angle, or CHA, refers to the angular range associated with a non-collimated incident beam, and is measured from the AOI to the largest cone angle.

Changing the AOI or CHA of your incident light will change the spectral response of the filter.  For more information on how different types of Semrock filters respond to changes in AOI, please review our technical note: Filter Spectra at Non-normal Angles of Incidence.  The spectral response to CHA is dependent upon many factors, so please contact technical support to discuss your specific application.

The AOI and CHA ranges for which filter performance is guaranteed are listed in each filter's Specifications tab on the website.  The AOI and CHA specifications given are exclusive; filters may not meet specification when incident light has non-zero value for CHA and AOI.