VIA Technologies EPIA SN-Series Specifications download pdf (Page 26)

Background

Figure 12: LEO Conditions

Figure 13: GEO conditions

Figures above refers to the hFOV (Half Field of View) and lead to a maximum full

aperture of 136.04° for LEO conditions and 20.2° for GEO. In order to achieve these

performances with a sufficient image quality, an all reflective systems (which not suffer

chromatic aberrations) may not be an appropriate choice due to the optical obscuration of

some configurations (Cassegrain) which becomes relevant at these wavelengths and

mainly because of the their small FOV which can‟t satisfy LEO requirements. Another

critical aspect is represented by the alignment of the system especially in case of off axis

mirrors. A refractive system instead, can reach large FOVs maintaining an adequate

image quality in term of optical aberrations and distortion due to the use of Germanium

(with a refractive index n=4) for the thermal IR wavelengths (8-14 µm). This permit to

achieve LEO requested values of FOV with a relative small amount of optical elements,

as shown in the following figures.

Figure 14: LCCES LEO optical layout

Figure 15: LCCES GEO optical layout

Each optical configuration has been preliminarily evaluated using a CAO (Computer

Aided Optics) software, OSLO, finding the expected values of aberrations (1

, 3

and 5

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VIA Technologies EPIA SN-Series Specifications Page 26