Ball averaging evaluation – Spheric Calibration

calliball - Reference Sphere CalibrationA Simple Ball Averager for Reference Sphere Calibration

When measuring the form errors of precision optics with an interferometer, calibration of the reference wavefront is of central importance. In recent years, ball averaging, or random ball testing, has emerged as a robust method for calibrating spherical reference wavefronts in converging beams.

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Calibration of transmission spheres

Calibration of Interferometer Transmission Spheres

Robert E. Parks Precision Machining Research Facility, NIST

This paper describes an inexpensive, quick and self-consistent method of calibrating spherical transmission optics where there is a real focus of the diverging test beam outside the transmission optic. The method is self-consistent in the sense that any given test result provides a means of calculating the variance of the result and requires no additional optic that must be calibrated or traced to another standard.

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Illumination cabinet for Scratch & Dig assessment

New from Armstrong Optical – Illumination Cabinet for all surface evaluation operations eg S/D comparisons


As part of our effort to supply complete solutions to end-users we have identified that there appears too be no commercial supplier of an illumination cabinet for use in the evaluation of for example,  Scratch/Dig against the internationally recognised standards – MIL-13830, or Scratch against ASTM Scratch Test Standard (Glass) adjunct F-428.



Because of this lack of off-the-shelf product we have developed a cabinet with cold-light illumination that meets the MIL-13830 illumination criterion and allows flexible use for all surface evaluation purposes. The cabinet dimensions are 65 (W) x 45 (D) x 62 (H) cm making it an ideal fit for a bench in the QA laboratory.



If you would like more information about the Illumination Cabinet please either call us on +44 (0) 1604 654220 or CLICK HERE to put your questions in an email.

Also see our Scratch & Dig reference articles – S/D references and our non-contact optical metrology solutions for S/D chraceterisation

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Scratch & Dig Samples from Davidson Optronics

Davidson Optronics, Scratch & Dig Samples

scratch & dig Davidson

Inspecting and characterising surface quality of finished optical components e.g.: lenses, prisms, mirrors, reticles, windows and wedges in accordance with MIL-13830, MIL-C-48497 and the new ANSI/OEOSC OP1.002:2008 is easily accomplished using these scratch & dig sample sets. The samples serve as direct visual comparison standards.

Each set consists of ten individual samples in a fitted hardware case. Samples are hermetically sealed as stand-alone pieces with a size of 1.5 x 1.5 x 0.375 inch (38 x 38 x 10 mm)

Values are:  Scratch 10 – 20 – 40 – 60 – 80   |   Dig: 5 – 10 – 20 – 40 – 50

Order set D-667, or D-667A, for a set with half-aluminised scratch samples (useful for characterizing highly reflective and/or polished metal surfaces).

Scratch & Dig Data Sheet

Conforms to ANSI/OEOSC OP1.002:2008
Certificate of Calibration Supplied
Compliant to MIL-O-13830 Rev. L


Please also review a portable illumination cabinet from Armstrong Optical to compare standards and your samples  – Cabinet link


For more information please call Armstrong Optical (+44 (0)1604 654220) or CLICK HERE


Price: £0.00