Hi Dialists, I've been reading with interest the messages on the Shadow Sharpener. My experience has been that though a Shadow Sharpener uses a "pin hole" it is more than just casting a pin hole image of the Sun (as proposed by several Dialers). The much increased precision of the Shadow Sharpener is obtained by casting a pin-hole image of the gnomon (wire, ball or building edge) in the center of a pin-hole image of the Sun (as described by Charles). This is done with a single pin-hole (which can often be as large as 1/8" depending on the distance to the gnomon) which is moved back and forth sideways to center the gnomon's image in the Sun's image. This can be done quite precisely, and the image of the gnomon is quite sharp, enabling a reading much closer than possible with the 1/2 degree penumbra of the Sun (as verified by Roger Bailey's experiments).
A wire or a bead that subtends 1/2 degree (1/8" at a distance of 14") when viewed from the scale or surface on which the shadow falls, will just obscure the Sun (as pointed out by Art Carlson). It will cast a tiny, dark umbra that can be closely read, but not as closely as the centered image of the Shadow Sharpener. Keep on looking at shadows! Bill
