title: Laser differential confocal ultra-long focal length measurement.
abstract: A new laser differential confocal focal-length measurement method is proposed for the measurement of an ultra-long focal-length. The approach proposed uses the property of an axial intensity curve that the absolute zero precisely corresponds to the focus of the objective in a differential confocal focusing system (DCFS) to measure the variation in position of DCFS focus with and without a measured ultra-long focal-length lens (UFL), uses the distance between the two focuses to obtain the UFL focal-length, and thereby achieving the precise measurement of ultra-long focal-length. The method has a high focusing precision, a strong anti-interference capability and a short measurement light-path. The theoretical analyses and preliminary experimental results indicate that the relative measurement error is about 0.01% when the method is used for the measurement of back-focus-distance (BFD).
authors.affiliation: Key Laboratory of Photoelectronic Imaging Technology and System, Ministry of Education of China,Beijing Institute of Technology, Beijing 100081, PR China. zwq669@126.com
authors.forename: Weiqian
authors.initials: W
authors.lastname: Zhao
authors.forename: Ruoduan
authors.initials: R
authors.lastname: Sun
authors.forename: Lirong
authors.initials: L
authors.lastname: Qiu
authors.forename: Dingguo
authors.initials: D
authors.lastname: Sha
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000295:instrumentation* / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation*; D007909:Lenses; D018613:Microscopy, Confocal / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity