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Dear Dan, I am also intrigued in pinhole sundials, and reflection ones too. I
tried to find the ratio between the wall (or floor) distance and the diameter
of the sun image on it. Assuming an average sun apparent diameter of 0,5° and a
unitary pinhole the ratio is about 114.59. If the ratio is smaller than 114
then fuzziness increases, at the point of loosing the round shape and taking
the shape of the mirror. When the ratio is higher the image is sharper. Gianni
Ferrari suggested a value for the wall distance of 300-400 times the pinhole
diameter, if I remember well. With such numbers the pinhole shape is ininfluent
on the image on the wall, which is always round. The general level of
illumination of the wall is also important for the final contrast of the light
spot. Cheers Francesco FERRO MILONE Turin
Inviato da Yahoo Mail su Android
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