Abstract
Linear astigmatism aberration is undesirable because it rapidly degrades image quality. We discuss some techniques to control and mitigate this aberration, and provide a comparison of lens systems that have been desensitized for linear astigmatism aberration.
Highlights
Our study focuses on the control of linear astigmatism aberration
This paper discusses the control of linear astigmatism aberration in a perturbed lens system
A first way to mitigate linear astigmatism is to desensitize a lens, a second way is compensation, and a third way is by assembling trials
Summary
Sometimes called central coma [5], is often a problem in high numerical aperture systems and can be corrected by decentering a lens element This has been done in assembling microscope objectives and in some early projection lenses for micro lithography. Another way to correct for uniform coma is reprocessing a system surface at the stop aperture location to introduce the opposite amount of uniform coma and rely on coma cancellation. This paper discusses several methods to mitigate linear astigmatism aberration in a system that is nominally axially symmetric but that due to fabrication and assembly errors suffers from this aberration. In projection lenses not discussed in this paper are using off-axis illumination and image processing [16]
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