Paraxial approximation: Difference between revisions

Revision as of 09:32, 29 October 2012

Revision as of 17:28, 20 November 2012

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:<math> \cos \theta \approx 1 - { \theta^2 \over 2 } \ .</math>

The paraxial approximation is accurate within 0.5% for angles under about 10°{{Citation needed|date=May 2011}} but its inaccuracy grows significantly for larger angles.

For larger angles it is often necessary to distinguish between [[meridional ray]]s, which lie in a plane containing the [[optical axis]], and [[sagittal ray]]s, which do not.