Arthur Carlson <[EMAIL PROTECTED]> writes: > ... What you really want is readability, which is a > compromise between brightness and blurriness for any pinhole. ... > ... Extending this logic, a vertically elongated pinhole > in a vertical plane might have some advantages over > either of the other arrangements. Hmmm.
Surely the problem with this is that the slit (which it will logically become if elongated enough) will not cast a line of light onto a mark on the dial at the same time throughout the year as the Sun's declination varies, except on the vertical (noon) line? (Of course this is absolutely fine if you just want a noon mark!) Moreover the elongation of the slit will decrease the accuracy of reading the declination. The former objection is of course overcome by making the slit polar instead of vertical so that you have an "ordinary" polar gnomon but which casts light instead of darkness ... I suspect some compromise is needed in the end - Tony's .gif showed how even for a very shallow countersink there comes a time when its bevel intersects the light. In any case the vertical hole may work better at higher latitudes with lower solar altitude, as it will become nearer to the normal hole anyway. But it's not obvious to me that the vertical hole will generally produce a much less readable spot than the normal one. Can anyone comment on that? Regards Andrew James
