Abstract
One of the key concerns in thin-film filter based spectral cameras is the presence of spectral shift in the measurements. This shift is caused by the sensitivity of the filters to the angle of incidence. In previous work, we showed that this shift can be corrected using a mathematical model. This model, however, requires knowledge of the distance to the exit pupil of the lens, which is not always readily available. We present a new model-based approach to estimate the distance to the exit pupil based on the observed spectral shift, making the method relevant for any thin-film Fabry-Perot based camera design. To implement the method, only a standard spectral camera setup and a well chosen spectral target are required. We also discuss how to optimally select such a target.
Highlights
Spectral cameras combine photography and spectroscopy and measure a spectrum for each point in the scene
We present a new model-based approach to estimate the distance to the exit pupil based on the observed spectral shift, making the method relevant for any thin-film Fabry-Perot based camera design
When spectral cameras are used to discriminate between samples it is essential that the measured spectrum does not depend on the object’s position in the scene, which could make physical interpretation impossible
Summary
Spectral cameras combine photography and spectroscopy and measure a spectrum for each point in the scene. Because thin-film filters are sensitive to this incident angle, this will cause undesired shifts in the measured spectra across the imaging plane (Fig. 1b). The shift depends on the position d of the filter, the size of the aperture and the distance x to the exit pupil. The distance to the exit pupil is often not known for arbitrary camera systems This is because the position may depend on several factors including the focus and zoom settings, how the lens is mounted, and the presence of other optical components (e.g. filters) in the optical path.
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