Unobscured two-mirror catadioptric optical system for a multispectral imaging apparatus

An optical system for a multispectral imaging apparatus, the optical system comprising:

• a primary mirror including a concave reflecting surface, the concave reflecting surface being an off-axis portion of a first mirror shape having a first optical axis;
• a secondary mirror including a convex reflecting surface oriented to receive light reflected from the concave reflecting surface of the primary mirror, the convex reflecting surface being an off-axis portion of a second mirror shape having a second optical axis laterally offset and tilted relative to the first optical axis;
• a first beam splitter oriented to receive light from the secondary mirror, the first beam splitter being configured to direct a first spectral band along a first path, and to direct a second spectral band along a second path;
• first refractive relay optics including a first plurality of refractive elements having respective optical axes oriented along the first path;
• second refractive relay optics including a second plurality of refractive elements having respective optical axes oriented along the second path;
• a first sensor positioned to receive light in the first spectral band from the first plurality of refractive elements;
• a second sensor positioned to receive light in the second spectral band from the second plurality of refractive elements;
• wherein the primary and secondary mirrors are configured such that a ratio of an equivalent diameter of an aperture of the primary mirror to the separation between the primary and secondary mirrors is greater than or equal to 0.75;
• and
• wherein the first and second refractive relay optics are configured to correct aberrations in the first and second paths formed by the primary and secondary mirrors so that the first and second paths focus on the first and second sensors, respectively.