Hi Dialling colleagues, Patrick Powers asked if anyone had practical experience of the bead-in-a-hole (pinspeck) shadow sharpener.
I used one experimentally o my Isaac Newton mean-time equatorial dial (see www.flowton-dials.co.uk). It consisted of a 3mm dia phosphor bronze bead suspended in a 5.5mm hole in a piece of brass shim. The dial plate was a cylinder radius 240mm. These values were chosen partly by experiment and partly by materials available. The sharpener worked well at noon, when the shadow appeared about 2mm in diameter in a bright annulus. However, at 9am or 3 pm, when the sun hit the nodus at 45 degrees to the axis, the shadow merged into the sides of the surround. This could have been avoided by having a nodus which rotated to face the sun but the extra complication wasn't worth the effort. In the end, I went with a simple hole 2mm dia, giving an apparant spot of 5 to 6mm at noon. The results (including a picture of the resulting shadow) were published in the Bulletin of the British Sundial Society, vol 14(i) March 2002. Anyone else tried one? John Davis Dr J R Davis Flowton Dials N52d 08m: E1d 05m -
