Contract Testing: Spectral Weighting

As is well known, due to dispersion the actual path of rays through refractive optics depends on the wavelength of the light. Therefore optics designers are modelling the propagation of rays through refractive optical elements such as lenses for various wavelengths. The spectral weighting, represented in optical design software by the number of rays per wavelength, should match the spectral sensitivity of the imaging sensor supposed to be used with that lens. A photographic taking lens for example requires a different spectral weighting than a lens that is designed for use in industrial image processing.

When a lens shall be tested with respect to its image quality by a measurement of the modulation transfer function (MTF) it is wise and important to conduct this measurement with a spectral weighting matching the one that has been used for modelling as close as possible.

In case of our MTF contract testing you can choose from a set of three standard spectral weightings covering the most popular applications of lenses:

1. CCD Semiconductor Camera without IR-Cut

This spectral weighting covers many applications in industrial image processing where the lens is used on a CCD semiconductor camera without any IR cutting filter. The spectrum ranges from some 400nm to about 950nm with following 11 equidistant nodes:

wavelength/nm	425	475	525	575	625	675	725	775	825	875	925
rel. amplitude weight %	55.2	78.2	95.3	99.3	94.8	90.1	81.7	72.7	61.6	46.6	32.3
rel. area weight %	6.8	9.7	11.8	12.3	11.7	11.2	10.1	9.0	7.6	5.8	4.0

2. CCD Semiconductor Camera with IR-Cut

This spectral weighting covers many applications in industrial image processing where the lens is used with a CCD semiconductor camera and an IR cutting filter. The spectrum ranges from some 400nm to some 700nm with following 6 equidistant nodes:

3. Consumer Photo

This spectral weighting covers the wide field of digital photo taking. The spectrum again ranges from some 400nm to some 700nm with following 5 nodes:

Further spectral weightings are available on request.