>The design which worked the best was a 1/8 inch spherical bead, suspended by >thin brass crosswires, in the exact center of a 1/4 inch round hole. (The >style was about 24 inches from the analemma). > >A very curious thing happens with this type of style. The bead alone, by >itself, casts a shadow that was twice as big as the bead; but when the 1/8th >in. bead is in the center of a 1/4" hole, with a space of 1/16th of an inch >between the bead's edge and the hole edge, the bead's shadow miraculously >sharpens into a tight, dark shadow that is only 1/16th of an inch in >diameter, smaller than the bead itself!!!! The wires which keep the bead >suspended in the middle of the hole are so thin that they don't cast a >visible shadow onto the analemma.
<snip> >I don't know why this works, but it does. Can any of you explain this? > >John Carmichael Although there may be some slight effect due to diffraction, it is negligible. The open ring between the bead and the edge of the hole can be described another way, as follows: The open ring is comprised of an infinite number of round holes, 1/16th inch in diameter, each with it's center on the circumference of a circle 3/16ths inch in diameter which is coaxial with the bead and the hole. Each of these 1/16th inch holes acts as a shadow sharpener (pinhole) which projects an image of the sun onto a surface. On the surface, there are then projected an infinite number of images of the sun arranged in a circle. The images overlap each other to form a bright ring with a dark center. As the bead/hole aperture is moved further away from the surface, the images of the sun will grow larger, overlapping more and more which causes the dark center to diminish in size. If the aperture is moved a large enough distance away, the dark center will disappear and the infinite number of sun images will almost merge into a single image of the sun. I say almost, because the centers (indeed any point on the sun) will still form a ring 3/16ths inch in diameter. Does that make any sense? Charles
