High precision focus correction system for multispectral filter-wheel cameras

Maik Rosenberger,Richard Fütterer,Alexander Wemhoff,Marc Preissler,Gunther Notni,Paul-Gerald Dittrich,Mathias Schellhorn

doi:10.1088/1742-6596/1065/3/032014

Maik Rosenberger, Richard Fütterer + Show 5 more

Open Access

https://doi.org/10.1088/1742-6596/1065/3/032014

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Abstract

Spectral Imaging is one of the current topics in science and industry. To capture spectral images many investigations were made in the past and will be done in the future. For reasonable and robust results in spectral imaging, a high image quality should be provided. One part of all spectral imaging systems is the optical system beside illumination and sensor characteristics. Lenses with a low chromatic aberration or systems, which can correct these aberrations, will lead to good image quality as mentioned. This article will show an approach to correct the chromatic aberrations, which is natural generated in refractive lens systems. This is realized by moving the image sensor with a very high precision. Therefore, investigations considering the accurate bearing of the sensor as well as an evaluation of the system characteristics were done and explained in this paper. Finally, the image sensor can be placed in less than microseconds with a micron accuracy of less than a pixel of the sensor. The tilt along the moving axis stays below one micron.

Highlights

Multispectral imaging systems based on filter wheels suffer from strong chromatic aberration, i.e. for each wavelength present on the illumination source, a slightly different focal position is achieved
The required throw force is limited by two thresholds: in minimal deflection under bending load, the remaining initial spring force has to be greater than the weight of the image sensor including support
The maximum force is limited by the actuator and should be as low as possible to save energy; reduce friction; and allow a high dynamic

Summary

Introduction

Multispectral imaging systems based on filter wheels suffer from strong chromatic aberration, i.e. for each wavelength present on the illumination source, a slightly different focal position is achieved. With the spring deflection along the z-axis a shift downwards in the negative y-direction leads to a displacement. For the image sensor movement all displacements changing the spatial information in x and y have to be avoided. The required throw force is limited by two thresholds: in minimal deflection under bending load, the remaining initial spring force has to be greater than the weight of the image sensor including support. The maximum force is limited by the actuator and should be as low as possible to save energy; reduce friction; and allow a high dynamic.

Results

Conclusion