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Form and Wavefront Metrology

Working Group 4.21

Transmission measurement for beam-shape-changing optical components

The transmission measuring set-up described in the following allows the spectral transmittance to be determined for beam-shape-varying optical components. These may be telescopes, photographic objectives, lenses, microscope objectives or other light-absorbing components.

The measurement of the spectral transmittance serves to determine the colour fidelity and/or the colour filtering of optical components. The spectral transmittance is determined with the aid of a limited beam which is incident parallel to the axis via the measurement of the ratio of the radiant power with and without sample.

From these two measurement values, the spectral transmittance τ(λ) of an optical component can be determined. Standard DIN ISO 14490-5 is used as a basis.

If, at the wavelength λ, the radiant power incident on the test specimen is Φo(λ) and the radiant power emerging from the test specimen Φ(λ), the spectral transmittance τ(λ) is obtained as follows:

τ(λ) = Φ(λ) / Φo(λ).

The result is a quantity without unit, which is indicated in percent for each measured wavelength.

The transmission is determined in the spectral range of (400 ... 1300) nm with an expanded measurement uncertainty of 1,2 % in the transmission range from 10 % to 100 %.

Measuring facility used at PTB
Principle of measuring instrument
3D model of the setup for transmission measurement for beam-shape-changing optical components