How big is the JWST mirror?
The JWST primary mirror is made of 18 segments and stretches 6.6 meters from tip to tip. Its area of slightly more than 25 square meters and its diffraction-limited resolution are approximately equivalent to a 6.0 meter conventional round mirror. At 2 microns, the FWHM of the image will be about 70 milli-arcsec. The 18 hexagonal segments are arranged in a large hexagon, with the central segment removed to allow the light to reach the instruments. Each segment is 1.32 m, measured flat to flat. Beginning with a geometric area of 1.50 m2; after cryogenic shrinking and edge removal, the average projected segment area is 1.46 m2. With obscuration by the secondary mirror support system of no more than 0.86 m2, the total polished area equals 25.37 m2, and vignetting by the pupil stops is minimized so that it meets the >25 m2 requirement for the total unobscured collecting area for the telescope. The outer diameter, measured along the mirror, point to point on the larger hexagon, but flat to f
