Tom McHugh wrote:
>The ultimate limitation would be diffraction (i. e., the reason why a photo
made
>with a pinhone aperture is not as sharp as a photo of the same plate scale made
>with a lens, and can never be as sharp). Also, there is the confusion of shadow
>line caused by the width of the light source--the Sun, about 31 minutes of arc.
>
>These two factors put a practical limit upon the fineness of scale division
on any
>kind of a sundial, irrespective of the size of the dial, or the acuity of
vision of he
>who reads the dial.
Hi Tom:
I'm sure you are right about diffraction being the ULTIMATE limitation of
precision. But the message that I was trying to get across is the
difference in the minimum separation of engraved lines that is mechanically
and structurally possible in stone and metal. I just wanted to make the
point that stone will become weak and may fracture if lines are engraved too
closely, whereas lines on metal can be much closer. I was also trying to
point out that because of the difference in metal and stone working tools,
that the actual lines on metal can be thinner than lines on stone. I might
add that these limitations also are true for any other dial furniture and
artwork.
Sorry I did not explain it a little better.
John Carmichael
>
