Wide field-of-view all-reflective objectives designed for multispectral image acquisition in photogrammetric applications

In many aerial and close-range photogrammetry applications, the near infrared (NIR) spectral range is required in addition to the visible (VIS) spectral range. Currently, many especially aerial photogrammetric systems use particularly optimized camera systems for each spectral band. Using separate cameras or lenses can introduce parallaxes and time-delays between the acquired images, and thus complicate the data fusion process. Furthermore, it adds additional weight to the entire system. With an image acquisition through a single objective, the complexity of the data fusion and the weight can be significantly reduced. However, to be able to only use one objective for different spectral bands, the optical system has to be free of chromatic aberrations. For photogrammetric applications, a wide field-of-view and a high resolution are frequent additional requirements. Therefore, we will present a design and an adapted photogrammetric calibration method of an all-reflective unobscured optical system optimized for full-frame imaging sensors. All-reflective unobscured optical systems may also be a very efficient imaging tool in combination with unmanned aerial vehicles (UAVs). Due to the limited payload capacity, many currently available UAVs can only be used with one spectrally limited camera system at the same time. With miniaturized all-reflective camera systems, the image data could be acquired in the visible and e.g. the NIR spectral range simultaneously