This is embarrassing, but I've just repeated the pinhole experiment with the setting sun which is about 15 degrees high and I must conclude that the results of my earlier test that I did at noon were flawed. At noon I had tried to hold the pinhole and projection screen at odd angles to simulate a setting sun while holding the whole thing in the penumbra (Not to easy a thing to do). I must have held them wrong and drawn the wrong conclusion. Besides, Mac is one of those sundial people who I most respect and I just couldn't believe he could make a mistake. The solution to convert an elliptical image into a circle by holding the pinhole parallel to the ground does not work.
This time, an hour before sunset, my projection screen was horizontal and I held my 2mm pinhole 1 meter away. I used full sunlight, no penumbra. Holding it perpendicular to the sun produced an ellipse, and tilting it slowly so that it is parallel to the ground causes a dimming of the image, but the images remains the same shape and does not become a circle. Maybe for these low sun markings, I could devise some sort of tilted little screen that is positioned above the timeline that will be perpendicular to the sun rays so that it would have a circular image. I'll have to think about that. John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> ----- Original Message ----- From: "John Carmichael" <[EMAIL PROTECTED]> To: "Sundial List" <[email protected]> Cc: "Rob WM. Vugteveen" <[EMAIL PROTECTED]> Sent: Thursday, June 13, 2002 12:44 PM Subject: Image Problem Solved! > Problem solved! > > Mac Oglesby just solved the image ellipse problem that I had with the > pinhole sharpener when the sun is low. I had been holding my sharpener > perpendicular to the sun's rays which produces an elongated image of an > ellipse around sunrise and sunset. He said that if I hold the sharpener > parallel to the ground, that the image becomes round. I didn't believe him > and thought it impossible, but both Edley and I just tested it and Mac's > right! Although as Edley noted to me, the image is dimmer, but that's no > problem.(Using some tilting of the planes because its midday here). > > Thanks Mac! > > John > > John L. Carmichael Jr. > Sundial Sculptures > 925 E. Foothills Dr. > Tucson Arizona 85718 > USA > > Tel: 520-696-1709 > Email: [EMAIL PROTECTED] > Website: <http://www.sundialsculptures.com> > > - > -
