Abstract: A multiple field-of-view telescope and optical sensor system and imaging methods using the system. In one example, an optical sensor system includes a primary imaging detector having a first field of view, a telescope configured to receive and focus electromagnetic radiation onto the primary imaging detector along a primary optical axis, a secondary detector having a second field of view different from the first field of view, and relay optics configured to direct and focus a portion of the electromagnetic radiation onto the secondary detector. In certain examples, the system further includes a fold mirror positioned to reflect the portion of the electromagnetic radiation to the relay optics.