title: Measurement of the numerical aperture and f-number of a lens system by using a phase grating.
abstract: A simple method for measuring both the numerical aperture and the f number of a lens system by means of a phase grating is described.
authors.forename: F
authors.initials: F
authors.lastname: Lei
authors.forename: L K
authors.initials: LK
authors.lastname: Dang