Summary of the High Accuracy Aperture Measurement Capabilities at the National Institute of Standards and Technology
J B. Fowler, Robert D. Saunders, Albert C. Parr
The determination of the geometrical and the effective area for optical quality apertures is one of the fundamental sources of uncertainty in many radiometric and photometric measurements. The National Institute of Standards and Technology has developed two non-contract instruments for measuring the area of these optical apertures. Some details of the instruments and their capabilities will be presented. Both instruments can be used to measure the area for apertures with diameters ranging from 3.5mm to 25mm. The measurements using the absolute instrument result in k=2 relative uncertainties ranging from 0.003% for 25mm diameter apertures to 0.005% for 3.5mm diameter apertures. There is some dependence of the uncertainty on the quality of the edge and the aperture diameter. The measurements using the relative instrument result in k=2 relative standard uncertainties ranging from .02% for 25mm diameter apertures to 0.03% for 3.5 mm diameter apertures assuming adequate edge quality. For apertures with very poor optical edge quality, the difference between geometrical and effective area can be as high as 0.3%. The increased uncertainty is due largely to scattering from the edge. Both instruments play a major role in the CCPR aperture area inter-comparison program, which began in 1999.
, Saunders, R.
and Parr, A.
Summary of the High Accuracy Aperture Measurement Capabilities at the National Institute of Standards and Technology, Metrologia, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=841396
(Accessed November 30, 2023)