ImagingPath.NA

raytracing.ImagingPath.NA(self)

This function returns the numerical aperture of the component or imaging system, which is the sin of the axial ray angle, times the index of refraction.

It is not always appreciated that the NA of an optical system is meaningful mostly in “finite conjugate” situations, that is, when either the object and the image are at small, finite distances. In practice, this means microscope objectives and 4f relays for example. On the other hand, infinite conjugate systems are better described by their f-number. A system is designed as either a finite-conjugate system or an infinite-conjugate: this is a design decision. See Smith “Modern Optical Engineering” Section 6.7 Apertures and Image Illumination.

Returns:: NA
Return type:: float