ImagingPath.fNumber

raytracing.ImagingPath.fNumber(self)

This function returns the f-number of the component or system by dividing the diameter of the entrance pupil by the effective focal length of the system.

It is not always appreciated that the f-number of an optical system is meaningful mostly in “infinite conjugate” situations, that is, when either the object or the image is at infinity. In practice, this means with photography and telescopes for example. On the other hand, finite conjugate systems are better described by their NA. For elements, we calculate the f-number of lenses by assuming they are used with an object at infinity. 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:: fNumber
Return type:: float