National Physical Laboratory

Power and Radius of Reference Lenses (spherical, cylindrical and prismatic lenses in the range ± 0.05 dioptres to ± 25 dioptres)

Interferometric lens testing facilityThe interferometric lens testing facility at NPL Measuring wavefront errorMeasuring wavefront error 

Measurement of spherical surfaces by interferometry

An important factor in achieving accurate production of spectacle lenses is the maintenance of consistent standards of lens power in the ophthalmic examination, lens manufacture and subsequent spectacle fitting. Consistent measurements of power may be assessed in all these stages by using focimeters and spherometers which have been calibrated with suitable reference lenses.

NPL offers a range of services in support of accurate ophthalmic measurements including the calibration of customer supplied reference lenses, the provision of boxed sets of calibrated ophthalmic reference lenses, and the calibration of focimeters.

Key features

  • Calibrations traceable to national standards
  • Calibration of the power of reference lenses in the range ± 1 dioptre to ± 25 dioptres. Measurement uncertainty ± 0.005 dioptres to ± 0.02 dioptres
  • Calibration of the power of weak lenses in the range ± 0.05 dioptres to ± 1 dioptre. Measurement uncertainty ± 0.002 dioptres
  • Power measurements of spherical, cylindrical and prismatic lenses
  • NPL certificate of calibration issued

Associated services

  • Supply of boxed sets of calibrated ophthalmic reference lenses
  • Calibration of focimeters on and off site
  • Calibration of the optical properties of a Gaugemaster
  • Power measurement of contact lenses
  • Assessment of ophthalmic equipment and measuring processes


Customer Service tel: +44 20 8943 6245

Last Updated: 19 Mar 2012
Created: 1 Feb 2011


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