SOFIA Airborne Telescope Diameter

Like most modern research telescopes, the SOFIA telescope uses a mirror to concentrate and focus the incoming light. SOFIA’s telescope is usually referred to as a 2.5-meter meter telescope, rather than 2.7 meters, because the optical design requires that only about 90% of the mirror’s reflecting surface (called the "effective diameter") can be used at any one time. Although SOFIA’s telescope is by far the largest ever to be placed in an aircraft, compared to normal ground-based research observatories it is only medium-sized.

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