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9. Bundle Shape and -Size
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Of course the volume between object and lens and the volume between lens and image is filled with air (or with glass or other clear materials).
But anyway, baffles (see para. 10) and mechanical structure are necessary nearby.

Sometimes too near.

This can result in several imperfections of the image.

So we should thoroughly derive the actual cross sectional shape of the bundle wherever an unwanted intrusion might occur. How can we do that?
Let us consider a simple yet usual task: rectangular object and circular front lens.


fig.9: Deriving Ray Bundle Envelope (14kByte)

You just connect object rim and front lens rim by as many rays as possible. These form the envelope figure that encloses the complete ray bundle. A figure that you never should touch with any part.

If you intrude into this bundle, you inevitably cause unwanted shadowing or refraction or reflection ... or all three.

Shadowing near the object plane   O   will obscure the respective part of the object; shadowing near the principal plane   H   will obscure the entire image by the same fraction by which the front lens area is shadowed.

Intrusion with a refractive medium will cause image distortion. The nearer this intrusion is situated to the principal plane   H ,   the more distortion will occur.

Intrusion with a reflective medium will cause shadowing (see above) and stray light. Reflection near the object plane   O   will form a well-defined image (dark or light) of the reflecting area. As opposed to reflections near the principal plane   H ,   which will produce stray light that uniformly veils the entire image.

If you got only narrow space for your ray bundles, use your 3-D mechanical engineering program for assuring that your bundles remain untouched.



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Last modified Nov.26th, 2002 00:33