Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Targets. A. Modified Maltese cross with a diameter of 10 degrees. B. Horizontal lines with a width of approximately 22 degrees (spanning the aperture) and a height of 1.6 degrees. C. Low-pass filtered hourglass-shaped target with a width of 6 degrees and a height of 22 degrees. D. Unfiltered hourglass-shaped target.
