Re: Sundial Carpet
Thibaud Taudin-Chabot wrote: That sundial is not 1 spot projected on the floor, but the whole sundial pattern projected on the floor. On the floor you only need 1 readingmark, nothing more. I understand; I mentioned it as an example of dark spots being projected on the receiving surface, only... But the shadow of a spot on a window will be very difficult to find on a sunlit floor because the light of the sunlit floor is reflecting in every direction and also over the shadow spot so that shadow spot will be less clear. The bright spot of sunlight from a hole in a closed wall/ceiling will therefore much easier to find in a relative dark area. True! This will impact the choice of surface material, I'm sure. Dave -
Re: Sundial Carpet
That sundial is not 1 spot projected on the floor, but the whole sundial pattern projected on the floor. On the floor you only need 1 readingmark, nothing more. But the shadow of a spot on a window will be very difficult to find on a sunlit floor because the light of the sunlit floor is reflecting in every direction and also over the shadow spot so that shadow spot will be less clear. The bright spot of sunlight from a hole in a closed wall/ceiling will therefore much easier to find in a relative dark area. Thibaud Chabot At 08:40 06-09-2003 -0700, you wrote: Seriously, it should work fine. For yet another variant, see E. Roebroeck's projection sundial in the Netherland's, Dial 8 in the Stained Glass Sundials photopage, linked from http://tinyurl.com/frf4 Dave- -
Re: Sundial Carpet
On Sat, 6 Sep 2003, John Carmichael wrote: We're also discussing what I call antiaperture gnomon sundials. These are neat. Imagine a large clear pane of clear or light colored glass on a wall. And on this glass is a small very dark dot. Instead of a hole in a wall casting a beam of light, the dark spot casts a shadow onto the sundial face. (John Davis, do you have a term for these?) Does anybody have any opinions on the practical differences of using aperture gnomons versus antiaperture gnomons? John My goodness! A timepiece that uses a shadow as an indicator... What will they think of next? Seriously, it should work fine. For yet another variant, see E. Roebroeck's projection sundial in the Netherland's, Dial 8 in the Stained Glass Sundials photopage, linked from http://tinyurl.com/frf4 Very similar physics sets limitations on the size and resolution of an anti-aperture as on a true aperture. If I remember correctly, the ideal diameter of a hole is on the order of 1/107th the distance to the target. One advantage might be the relative simplicity of using one of the shadow sharpening ring apertures discussed last year. The spot placed on the clear window pane could easily consist of a dark ring, or even a series of rings, of decreasing width as the radius increases. Think of a Fresnel lens, implemented as alternating dark and clear rings. Dave -
Re: Sundial Carpet
On Sat, 6 Sep 2003, J. Tallman wrote: Perhaps there is a good ratio to use for dot/disc size vs. distance to the shadow field? Perhaps some of the list members know the answer to this... Jim 1/107 had stuck in my mind, and I made a quick test a few minutes ago. We have near-horizontal roof windows/skylights in our living room ceiling, so I checked out one of the patches of sun the cats follow across the carpet. A standard C9 Christmas light (just be quiet - maybe I'll take them down *next* year!) casts a fuzzy shadow at a distance of about 160 inches. That lamp size is about 1 inch diameter, and 2 inches long, for reference. Maybe later today, I'll print out some shadow spots on overhead projector film, and try some different configurations. Have to get out the Windex, first, though! Dave -
Re: Sundial Carpet
On Sat, 6 Sep 2003, Mac Oglesby wrote: 107:1 seems to be the ratio between the projection distance from a pinhole to a screen and the diameter of the Sun's image. That is, the diameter of the Sun's image will be about 1/107th of the distance from the projecting pinhole. Since a pinhole image is very dim, for brighter images, the ratio between the projection distance and the hole diameter is recommended as ranging from about 200:1 to 400:1. Hope this helps. Mac Isn't that reversed, Mac? If the image is too dim, you would want a larger pinhole, not a smaller one, as 200:1 or 400:1 would indicate... Dave -
Re: Sundial Carpet
I have also considered using this type of arrangement (a dot on a clear pane) for several projects in the past. I wonder just how big the dot would have to be? I assume penumbral effects would be at play, and the distance to the shadow receiving surface would probably be a factor in determining the best size of dot to use? Perhaps there is a good ratio to use for dot/disc size vs. distance to the shadow field? Perhaps some of the list members know the answer to this... Best, Jim We're also discussing what I call antiaperture gnomon sundials. These are neat. Imagine a large clear pane of clear or light colored glass on a wall. And on this glass is a small very dark dot. Instead of a hole in a wall casting a beam of light, the dark spot casts a shadow onto the sundial face. (John Davis, do you have a term for these?) Does anybody have any opinions on the practical differences of using aperture gnomons versus antiaperture gnomons? thanks John -
Re: Sundial Carpet
Hi Terry That's a wonderful idea too: a poor man's terrazzo! The original idea of the designing consultant was to have three separate aperture gnomon interior sundials in the building on the east, south, and west walls. (each dial would tell time/date for just a portion of the day) They are not opposed to having the sundial face drawings on the walls as well as the floors. We're also discussing what I call antiaperture gnomon sundials. These are neat. Imagine a large clear pane of clear or light colored glass on a wall. And on this glass is a small very dark dot. Instead of a hole in a wall casting a beam of light, the dark spot casts a shadow onto the sundial face. (John Davis, do you have a term for these?) Does anybody have any opinions on the practical differences of using aperture gnomons versus antiaperture gnomons? thanks John John L. Carmichael Jr. 925 E. Foothills Dr. Tucson Arizona, USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Sundial Sculptures Website: http://www.sundialsculptures.com Stained Glass Sundials Website: http://advanceassociates.com/Sundials/Stained_Glass - Original Message - From: [EMAIL PROTECTED] To: sundial@rrz.uni-koeln.de Sent: Saturday, September 06, 2003 3:23 AM Subject: Re: Fw: Sundial Carpet I have seen some decorative floors made from coloured linoleum. This material is now available in a wide range of colours, from pale pastels to dark rich shades (unlike the traditional drab brown). The floors are made rather like marquety or stained glass windows, by sraftsmen cutting intricate shapes which are stuck down to create any pattern or design. The neccessary markings for a sundial would be relatively easy for such craftsmen. I believe the material to be very hardwearing and suitable for areas of heavy traffic and wear. I have seen it laid in sports hall entrances and confereence venues etc. It can be sealed and polished and the material is self coloured so that a pattern cannot 'wear off'. It is easily cleaned by mopping and burnishing and does not fade. However it is not portable but therefore no problem then with movement or misalignment. Terry Quoting Len Berggren [EMAIL PROTECTED]: The effect of wind currents could certainly be minimized by a heavy cord or rope being sewn along the bottom of the banner. -Len That's a neat idea Claude! But it'd be susceptible to wind currents, wouldn't it? John John L. Carmichael Jr. 925 E. Foothills Dr. Tucson Arizona, USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Sundial Sculptures Website: http://www.sundialsculptures.com Stained Glass Sundials Website: http://advanceassociates.com/Sundials/Stained_Glass - Original Message - From: Claude Hartman [EMAIL PROTECTED] To: sundial@rrz.uni-koeln.de Sent: Friday, September 05, 2003 12:29 PM Subject: Re: Fw: Sundial Carpet This seems a valid concern. Would a hanging banner work? If thin enough or of the right quality cloth, it could be viewed from both sides in the hall/lobby. It would then be out of the way for visitor interference and wear. It could also be exchangeable for seasons, special occasions or whatever. Just another thought! Claude Hartman Sunlight Designs Edley McKnight wrote: Hi John, Although it sounds intriguing, fabrics/rugs stretch/shrink quite a bit, so I don't know how accurate this would be. Then again, if there are many people present, the sun spot might not actually reach the floor. The carpet might have to be often rewoven where worn, damaged or had stuff spilled on it. It does sound neat though. Maybe a woven wall hanging glued to a firm backing? Edley. Please excuse me if this is a resent message, but I'm resending because I don't think the original made it thru the internet. - Original Message - From: John Carmichael [EMAIL PROTECTED] To: Sundial List sundial@rrz.uni-koeln.de Sent: Wednesday, September 03, 2003 11:08 AM Subject: Sundial Carpet Hello All: A person who does solar consultations and experiments for architects (she uses a heliodon) contacted me after having viewed the Stained Glass website. A new library is being built in Washington state and she is wants to incorporate an interior sundial in the main lobby entrance. We discussed projection stained glass on the ceiling, and aperture gnomons dials on the wall. Talks are still underway with the design team, but we will probably use the aperture gnomon design that uses a hole in the southern wall that projects a beam of light onto a sundial face on the floor. When we discussed how to put the drawing on the floor, I suggested using a colorful design woven in the carpeting. I
Re: Sundial Carpet
Hi John, We're also discussing what I call antiaperture gnomon sundials. These are neat. Imagine a large clear pane of clear or light colored glass on a wall. And on this glass is a small very dark dot. Instead of a hole in a wall casting a beam of light, the dark spot casts a shadow onto the sundial face. (John Davis, do you have a term for these?) In my book, it's called a nodus!... Regards, John D Dr J R Davis Flowton Dials N52d 08m: E1d 05m -
Re: Sundial Carpet
Hello Jim, William Walton's Pinholes and Shadow Sharpeners and Gianni Ferrari's The Shadow Sharpener, each in Compendium 9-4, December 2002, deal with this question. 107:1 seems to be the ratio between the projection distance from a pinhole to a screen and the diameter of the Sun's image. That is, the diameter of the Sun's image will be about 1/107th of the distance from the projecting pinhole. Since a pinhole image is very dim, for brighter images, the ratio between the projection distance and the hole diameter is recommended as ranging from about 200:1 to 400:1. Hope this helps. Mac Hi John, I have also considered using this type of arrangement (a dot on a clear pane) for several projects in the past. I wonder just how big the dot would have to be? I assume penumbral effects would be at play, and the distance to the shadow receiving surface would probably be a factor in determining the best size of dot to use? Perhaps there is a good ratio to use for dot/disc size vs. distance to the shadow field? Perhaps some of the list members know the answer to this... Best, Jim We're also discussing what I call antiaperture gnomon sundials. These are neat. Imagine a large clear pane of clear or light colored glass on a wall. And on this glass is a small very dark dot. Instead of a hole in a wall casting a beam of light, the dark spot casts a shadow onto the sundial face. (John Davis, do you have a term for these?) Does anybody have any opinions on the practical differences of using aperture gnomons versus antiaperture gnomons? thanks John - -
