Understanding astigmatism

Short Description
Astigmatism in an aberration that results when an optical system focuses two … exhibits no astigmatism. The lens is symmetric in the horizontal and …

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Content
MAS450/854
Understanding astigmatism Spring 2003
March 9th 2003
.. Introduction
.. Spherical lens with no astigmatism
.. Crossed cylindrical lenses with astigmatism
.. Horizontal focus
.. Vertical focus
.. Plane of sharpest focus .. Implications for 3D objects .. Why does astigmatism happen in holography?
.. Inline holograms
.. Off-axis holograms .. Notes
.. See Also: .. Chapter 10: Off-axis holography (PDF) * .. Chapter 10 Appendix: horizontal and vertical focus (PDF) * .. MAS450 Astigmatism cut-out model (PDF)*
Introduction
Astigmatism in an aberration that results when an optical system focuses two orthogonal axes of light at two different distances in space. Holograms and holographic optical elements intentionally produce, or unintentionally suffer, from astigmatism. To explain the basic properties of astigmatism, though, we choose a simpler optical model using spherical and cylindrical refractive lenses.
Spherical lens with no astigmatism
The ideal version of the common spherical lens, of which a typical magnifying glass is an example, exhibits no astigmatism. The lens is symmetric in the horizontal and vertical directions (indeed, all directions), and thus has an optical power that doesn’t vary depending on whether the angle that light strikes the lens is…