optical design, engineering
& manufacturing |
Clearly Your
Choice for
PRECISION OPTICS |
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Aspheric Primer |
| Definition:
Aspheric optical surfaces are those who’s shapes are not constrained
to be spherical (or flat). In optical systems, the most commonly used
aspheric surfaces are rotationally symmetric and defined by this
equation (or a variation).
Z =sag height r
=radial distance from vertex C=curvature at
the vertex (1/radius of curvature) K=conic
constant A,B,C…=polynomial terms.
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| Why Aspheres?
The ability to shape a surface within an optical design
to something other than a sphere adds many extra degrees of freedom.
Often one aspheric component can replace 3 or more spherical
components. A simple example is shown here in which a plano-convex
BK-7 singlet is used to form a collimated beam of 644nm light at an
aperture ratio of F/1. |
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| Note
that the scale of the drawing is not exaggerated. Clearly the
aberrations are massive (over 670 waves!) By allowing the surface to
be an asphere the design performance can be made essentially perfect
(under .001 waves!) as shown here. |
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| To
achieve nearly perfect design performance with only spherical surfaces
and BK-7 glass, a 5 element system is needed. (____ waves) |
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| Or by
using a high index, higher cost glass of 3 element design will
suffice. |
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The use of aspheric lenses in the past
has been limited by costly manufacturing techniques. With our new
technology from Satishloh, the cost of producing an aspheric lens is
reduced to compete with a spherical system.
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© 2007 Kreischer Optics, Ltd. Revised April 2004.
Kreischer Optics - 1729 Oak Drive -
McHerny, IL 60050 - phone:
(815) 344-4220
/ email: optics@kreischer.com
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