What specific optical defect resulted from the mirror edges being ground too flat?
Answer
Spherical aberration
Because the outer edges of the mirror focused light slightly behind where the center focused, the defect experienced was known as spherical aberration, resulting in a smeared blob instead of a pinpoint image.

Related Questions
How much did the edges of Hubble's primary mirror deviate from the required curvature?What specific optical defect resulted from the mirror edges being ground too flat?Which contractor held the primary responsibility for grinding the flawed primary mirror assembly?What key hardware installed during SM1 acted as corrective eyeglasses for the telescope?What impact did the primary mirror flaw have on Hubble's expected clarity?In which month and year was the crucial first servicing mission (SM1) carried out?What specialized device, used to check the mirror's shape during manufacturing, was implicated in the failure to catch the error?What subsequent operational complexity was introduced by installing COSTAR?Which objects could scientists still observe with some success even before the mirror was corrected?What ongoing environmental challenge did the telescope's temperature control systems need to manage?