Gianni and John, A good front face mirror for the sun can be made from a scrap of ordinary window glass. Mark it with a glass cutter (or a carbide scribe) and make
controlled breaks along the pre-scribed lines to obtain the size you want. "Soften" the sharp edges and corners with "wet or dry" silicon carbide paper or an abrasive "stone". Place medium grit carbide paper on some flat horizontal work surface and rub the intended back of the glass till it is well frosted. (Use soapy water to lubricate for this step.) Wash up, let dry and apply black paint to the ground surface. Latex or oil based, matte or glossy, will serve. (The tiny grinding facets provide "matte"and effectively eliminate internal reflection.) You'll still need additional light filters, but brief accidental exposure to the sun's reflected image will not entail the very real risk that direct viewing presents. Sciagraphically, Bill On Mon, 08 Jul 2002 12:58:33 -0400 <[EMAIL PROTECTED]> writes: > > Great idea Gianni! > > Will have to try it. > > Thanks > > John C. > > On Fri, 5 Jul 2002 18:39:57 +0200 Gianni Ferrari > <[EMAIL PROTECTED]> wrote: > > > > 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] > > > > > > - > > > > - > -
