principal axis

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Two chicks near an egg with a white background (poultry, chick, chickens, birds).

What Do Eggs Have to Do with Easter?

New Zealand. Political/Physical map. Includes locator.

Where Is “Old Zealand”?

Groups of depositors in front of the closed American Union Bank, New York City. April 26, 1932. Great Depression run on bank crowd

Causes of the Great Depression

African Americans demonstrating for voting rights in front of the White House as police and others watch, March 12, 1965. One sign reads, "We demand the right to vote everywhere." Voting Rights Act, civil rights.

Timeline of the American Civil Rights Movement

Ahura Mazda - relief of the Zoroastrian god Ahura Mazda at the ancient ruins of Persepolis in Iran. Also known as Ormazd Zoroastrianism,

Which Religion Is the Oldest?

Titanic infographic. The 30th anniversary of its discovery is September 1, 2015. SPOTLIGHT VERSION.

Timeline of the Titanic’s Final Hours

Easter Procession of Maria Santisima del Sacromonte in Granada, Spain. This statue is known as Virgen de los Gitanos or The Virgin of the Gypsies.

What is Holy Week?

principal axis

optics

Learn about this topic in these articles:

principles of lens construction

In lens: Optical principles for lenses
…single straight line called the principal axis of the lens. A frequently used measure of the quality of any lens system is its ability to form an image that is sharp enough to separate, or resolve, two very close dots or lines in an object. Resolving power depends on how…
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