I have read with a lot of interest the numerous and very interesting
messages that concern the Shadow Sharpener and I would like to make a little
observation.
This doesn't concern the beautiful sundial of John Carmichael and the
clever methods described for the the use of the pin-holes sharpener, but
perhaps it could interest someone for other applications.
To see the image of the Sun together with that of a distant gnomon we can
use a different approach instead of using a S.S.
If we could put our eye on the plane (for instance in the place of a hour
line), looking toward the Sun (when the shadow of the gnomon passes on the
line) we would see the disk of the Sun and the gnomon with a great
sharpness.
Because we cannot put our eye on ( or under) the plane, we can put there a
small mirror and look in it directly: obviously the eyes have to be
protected or with eclipse glasses or with a Milar filter or with a
welding glass, etc.
To decrease the quantity of the light reflected it ispossible to replace
the mirror with a simple window glass.
With some patience we can see the sharpest possible image of the disk of
the Sun and of the gnomon without any defocusing phenomenon .
With a solar filter for binoculars or for a small telescope, the image can
also be magnified and observed with a very good precision.
Best wishes
Gianni Ferrari
44° 39' N 10° 55' E
Mailto : [EMAIL PROTECTED]
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