Hi Bill: Of course you are right that optical resolution is'nt that important when looking at the shadow's edge cast by a traditional solid gnomon. However, I think it is important for string, cable, rod or spherical gnomons. It is also important when designing the width and size of numerals, hour lines and other dial furniture. (especially for wall dials which need to be read from a distance).
Now Dave Bell's optical resolution table indicates the maximum distance values for the limits of "human resolution" as you say, but as someone mentioned, you would certainly want to make your drawings a little larger than these values so that even people with poor eyesight could read them. As you also alluded to, the designer must also check to make sure that his cable, rod or sphere isn't so thin and far away from the dial face that is only shows the fuzzy penumbra of the shadow. (see Ross McCluney's excellent article "The Fuzziness of Solar Shadows" in Compendium vol. 1, #3.) So I guess you're right, one should not depend solely upon the optical resolution table. It should only be used as a starting point and guide. The thickness of the gnomon (style) should also be checked, using Ross's fuzziness formula. But in then end, the best thing to do with a new design would be to verify readablity through experimentation. Thanks for your imput, it makes us think. John >Sorry to be a kill-joy, but I fail to see the utility of scribing hour lines >near the limit of human resolution, when the shadow's edge cast by a solid >(non-wire) gnomon is blurred by the 0.5 degree width of the sun. > > > >Bill Gottesman >Burlington, VT, USA >lat 44.47583, long -73.202581 > >
