Calibration of the HAO Standard Opal Filter Set

The spectral regions chosen were 450 nm, 550 nm, 650 nm and 800 nm. In summary, it is felt that the use of the direct radiation from the sun, thereby insuring the proper geometry for the measurements, and employing a silicon photodiode detector,whose response is extremely linear over a wide dynamic range, have significantly improved the accuracy of the transmittance measurements.