“The closer you get to perfection, the easier it is to screw it up.” Ain’t it the truth? This statement has a world of applications, but it was uttered by a researcher interviewed in an NPR story. He was referencing the careful grinding of critical lenses for a telescope located in Tucson, AZ. If you remember back to the launch of the Hubble telescope, Perkin-Elmer of Connecticut (no slouches when it comes to scientific optics), made a miscalculation in the primary lens grinding that left the Hubble producing subpar images initially.
Analysis of the flawed images showed that the cause of
the problem was that the primary mirror had been ground to the wrong shape.
Although it was probably the most precisely figured mirror ever made, with
variations from the prescribed curve of only 10 nanometers; it was too flat at
the edges by about 2,200 nanometers. This difference proved catastrophic, introducing severe spherical
aberration, a flaw in which light reflecting off the edge of a mirror focuses
on a different point from the light reflecting off its center. It had
to be corrected by a later shuttle flight and crew.
A commission established that the main null corrector, a
device used to measure the exact shape of the mirror, had been incorrectly
assembled—one lens was wrongly spaced by 1.3 mm. During the polishing of the
mirror, Perkin-Elmer had analyzed its surface with two other null correctors,
both of which correctly indicated that the mirror was suffering from spherical
aberration. The company ignored these test results, as it believed that the two
null correctors were less accurate than the primary device that was reporting
that the mirror was perfectly figured.
hard to come by when human beings are involved, apparently.