Astronomer Masanori Iye of the National Observatory of Japan blames the blurry appearance of meteor trails at about 100 kilometers altitude on the fact that they were photographed with telescopes focused at infinity. But optics teaches that any object much farther away than the focal length of the telescope is essentially “at infinity.” Wouldn’t a routine cause of fuzzy telescopic images—diffraction—be a more important reason for the blurred trails?

Dan Wilkins
Omaha, Neb.

For the telescope used in these observations, calculations indicate that improper focus causes much more blurriness than diffraction does, says Iye. —S. Perkins