Ben B. answered • 11/21/14
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Experience Aerospace Engineer with Master's Degree in Physics
Parallel rays hitting a parabola will focus at the focal point, so if the light source is at the focal point, then the result will be parallel rays going out.
Ben B.
Bill,
For a parabolic reflector, the rays converge to a point only if the incident rays are parallel to the axis of the reflector. Similarly, for a source at the focus that is not on the axis (off-axis), the outgoing rays will not be parallel. I am not aware
of any simple formula. This phenomenon, is known as "coma" for reflecting telescopes of short focal length. That is - the rays do not focus to a point, resulting in images that are clear only for objects (stars) that are near the center of view. For stars
that are off axis, the image does not appear as a point, but as a V-shaped object that looks somewhat like a comet. The coma effect is worse for object farther from the center line.
- Ben
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11/21/14
Bill C.
Hi Ben,
Great, thank for the information for I am striving to create a homogeneous light pattern with LEDs by using a spherical concave reflection and this will help.
Kind Regards,
Bill Cliff
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11/22/14
Bill C.
11/21/14