Re: Puzzle Photograph of the Eclipse - A complete guess
This is just a conjecture: I do not think this focused image of the eclipsed sun is a pin-hole artifact. My guess is that it is a focused image by the lens, but is a 2nd or 3rd internal lens relfection. In this manner, the image might be reversed, and its brightness greatly attenuated, so as to allow the sun appear to be displaced, properly exposed, and in focus. I don't see why the front surface of the lens would be hot. My guess about the red glow is that it is a completely different internal reflection, and that the circular nature of it is defined by the circular edge of a lens component. I think this would be analogous to a telescope's or binocular's exit pupil. -Bill On 1/5/2011 2:54 AM, Frank King wrote: Dear All, A collegue pointed his iPhone at the partially-eclipsed sun yesterday morning and sent me the result: http://www.cl.cam.ac.uk/users/fhk1/Eclipse11.jpg It is clear that the camera wasn't stopped down anything like enough but why, he asks, does he get a pin-hole artifact of the eclipsed sun? At this stage of the eclipse the crescent was the other way round from the way it appears in the artifact. This is what one would expect from an image created by a pin-hole but not when printed and turned the right way up! Could this be an image of the reflection in the water? I know almost nothing about iPhone camera technology and cannot give a convincing explanation of the physics behind this artifact. There is also the surrounding elliptical red background to explain. Could that be an image of the hot front surface of the lens? Any thoughts? Frank King Cambridge, U.K. --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Glass on Glass Mosaic Indoor Sundial Windows
I tested my cheapo magnets with double pane glass (1/4 thick) and the bonding force was a lot weaker- not strong enough to hold a small rod gnomon. Art Krenzel's super strong Neodymium magnets would surely work. He told me about this company that sells supper strong magnets at http://www.kjmagnetics.com They advertise them as the world's strongest magnets. They have just what we need! They're called Mounting Magnets. The top piece is cup shaped and fits nicely over the bottom magnet so they won't slip around. The top non-rustable stainless steel piece even comes with a threaded hole that you could screw a threaded gnomon rod into!!! And, they come in all sizes- including metric These things are PERFECT! Here is a sample of one of them. See: http://www.kjmagnetics.com/proddetail.asp?prod=MMS-D-XC They also have rubber, plastic and teflon coated magnets! See: http://www.kjmagnetics.com/products.asp?cat=164 Important Safety Warning! Read Before You Order and Use the Magnets Handling them with care is necessary to prevent personal injuries, property damages and magnet damages. 1. Neodymium magnets are brittle; they can be broken or can splinter in a collision. One should wear gloves and protective glasses when handling these magnets, because splinters could disengage and fly from the magnets. 2. Normal Neodymium magnets will lose their magnetic properties if heated above 175°F (80° C). Higher temperature rare earth neodymium magnets are available in our store. 3. The strong magnetic fields of neodymium magnets can damage items such as television, computer monitors, credit cards, bank cards, computers, diskettes and other data carriers, video tapes, mechanical watches, hearing aids, loud speakers and VCRs. Pace-makers may be damaged or switch to Test Mode in the presence of a strong magnetic force, if a pace-maker is in use, keep a minimum of 3 feet distance. 4. You should avoid having constant contact with magnets of any size and keep a distance of at least 3 feet to large magnets. 5. Children should not be allowed to handle neodymium magnets as they can be dangerous. Small magnets pose a choking hazard and should never be swallowed or inserted into any part of the body. 6. Under no circumstances should you try to cut, saw or drill the Neodymium magnets! Not only would the magnet break, but the resulting dust from the magnet is very flammable. Neodymium magnets should never be burned, as burning them will create toxic fumes. -Original Message- From: Mike Shaw [mailto:jmikes...@ntlworld.com] Sent: Tuesday, January 04, 2011 4:29 PM To: John Carmichael Cc: Sundial List Subject: Re: Glass on Glass Mosaic Indoor Sundial Windows John Nobody has mentioned double glazing yet. I assume that you don't bother with that in Arizona. Will the magnets still be OK to use through two thicknesses of glass with an air space between? Mike Shaw 53.37N 3.02W www.wiz.to/sundials --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Glass on Glass Mosaic Indoor Sundial Windows
p.s. Since these neodymium magnets are so strong, if they are too big, they may break the glass before falling off! I'm guessing that the magnetic bonding force is directly proportional to the area of the flat face of a disk magnet. The bigger the magnet, the more its bonding force. You might want to use a smaller size neodymium magnet with a gnomon for glass -Original Message- From: Mike Shaw [mailto:jmikes...@ntlworld.com] Sent: Tuesday, January 04, 2011 4:29 PM To: John Carmichael Cc: Sundial List Subject: Re: Glass on Glass Mosaic Indoor Sundial Windows John Nobody has mentioned double glazing yet. I assume that you don't bother with that in Arizona. Will the magnets still be OK to use through two thicknesses of glass with an air space between? Mike Shaw 53.37N 3.02W www.wiz.to/sundials --- https://lists.uni-koeln.de/mailman/listinfo/sundial
RE: Glass on Glass Mosaic Indoor Sundial Windows
p.p.s. Please excuse all these emails, but I'm telling you my ideas as soon as they come into my head. The smallest mounting magnet they make is just 5/8 diameter. This little guy packs a powerful force. It has a Pull Force of: 15.63 lbs See: http://www.kjmagnetics.com/proddetail.asp?prod=MMS-D-A The largest mounting magnet they have is 3 with an incredible Pull Force of: 352.4 lbs http://www.kjmagnetics.com/proddetail.asp?prod=MMS-D-Z0 John -Original Message- From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of John Carmichael Sent: Wednesday, January 05, 2011 9:48 AM To: 'Mike Shaw' Cc: 'Sundial List' Subject: RE: Glass on Glass Mosaic Indoor Sundial Windows p.s. Since these neodymium magnets are so strong, if they are too big, they may break the glass before falling off! I'm guessing that the magnetic bonding force is directly proportional to the area of the flat face of a disk magnet. The bigger the magnet, the more its bonding force. You might want to use a smaller size neodymium magnet with a gnomon for glass -Original Message- From: Mike Shaw [mailto:jmikes...@ntlworld.com] Sent: Tuesday, January 04, 2011 4:29 PM To: John Carmichael Cc: Sundial List Subject: Re: Glass on Glass Mosaic Indoor Sundial Windows John Nobody has mentioned double glazing yet. I assume that you don't bother with that in Arizona. Will the magnets still be OK to use through two thicknesses of glass with an air space between? Mike Shaw 53.37N 3.02W www.wiz.to/sundials --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Puzzle Photograph of the Eclipse - A complete guess
Dear Friends With all this talk of pinhole photography, I thought you might like the attached - taken over a continuous 6 month period by Justin Quinell of Bristol over the famous Brunel suspension bridge. He uses a beer can with a nail hole as his camera The photos are made on photo paper placed in the can. The image (after six months) is produced just by scanning the undeveloped paper! You can see all his various amazing solar pictures in proper size and how he makes them at ... http://www.pinholephotography.org/gallery/slow/index.html Enjoy Best regards Kevin Kevin Karney Freedom Cottage, Llandogo, Monmouth NP25 4TP 01594 530 595 inline: Brunel Bridge Pinhole.jpg --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Glass on Glass Mosaic Indoor Sundial Windows
Hi John, I notice that they also have a magnetic calculator: http://www.kjmagnetics.com/calculator.asp Roderick Wall. -Original Message- From: John Carmichael Sent: Thursday, January 06, 2011 3:47 AM To: 'Mike Shaw' Cc: 'Sundial List' Subject: RE: Glass on Glass Mosaic Indoor Sundial Windows p.s. Since these neodymium magnets are so strong, if they are too big, they may break the glass before falling off! I'm guessing that the magnetic bonding force is directly proportional to the area of the flat face of a disk magnet. The bigger the magnet, the more its bonding force. You might want to use a smaller size neodymium magnet with a gnomon for glass -Original Message- From: Mike Shaw [mailto:jmikes...@ntlworld.com] Sent: Tuesday, January 04, 2011 4:29 PM To: John Carmichael Cc: Sundial List Subject: Re: Glass on Glass Mosaic Indoor Sundial Windows John Nobody has mentioned double glazing yet. I assume that you don't bother with that in Arizona. Will the magnets still be OK to use through two thicknesses of glass with an air space between? Mike Shaw 53.37N 3.02W www.wiz.to/sundials --- https://lists.uni-koeln.de/mailman/listinfo/sundial - No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1191 / Virus Database: 1435/3359 - Release Date: 01/04/11 --- https://lists.uni-koeln.de/mailman/listinfo/sundial
More on Sundial Magnets
I offered the info below to John Carmichael, a long-time friend. John suggested I also copy the sundial reflector so here is what I sent to John earlier. John, I've followed the sundial list thread on using a magnet to secure a gnomon. Let me provide you some information about rare earth magnets. The most common magnet material is basically an iron/nickel alloy called Alnico; it is not a rare earth magnet but just about every common magnet you see is some form of Alnico. There are two common types of rare earth magnet material: neodymium iron boron (commonly referred to as just neodymium) and samarium cobalt. Samarium cobalt magnets can be more powerful (produce greater magnetic flux) and can operate at higher temperature. Samarium cobalt magnets typically cost more. Curiously, the expensive (because it is mined in only a few places in the world) element is the cobalt, not the samarium! Both types are typically plated with nickel and therefore look shiny. Both are quite brittle and don't survive mechanical shocks well. Even with the nickel plating, both types corrode when exposed to water vapor for extended periods. The adhesion of the nickel plating is not great and it is common to find it flaking off. The mutual attraction of either type is very strong and you can get yourself hurt if two magnets jump together and part of you is in between! Both types are also strongly attracted to steel and some stainless steels. The air (or, glass or plastic) gap between mutually attracted magnets strongly affects the attraction force. But, with either of the two common types of rare earth magnet you would not want direct contact as the separation force would be very high; I can easily imagine glass breakage before separating the magnets. Of course, the size and thickness of the rare earth magnet affects its field strength and attraction force so you could experiment with different sizes to select a pair with reasonable retention force. Where the poles are located on any magnet is determined by how the magnet was charged or initially magnetized. The raw material is not itself magnetic, it acquires residual magnetism by being subjected to a large magnetic field, usually in the form of a brief pulse from an electromagnet. But, location of the poles matters when you want mutual attraction between two magnets; magnets will self-align because opposite poles attract. So, you need to know where the poles are located to predict how the magnets will align to each other. A cylindrical magnet can have its poles on opposite faces or at 180° opposing *edges* rather than faces. Many magnets are made into special shapes to function with a moving armature to produce a motor or actuator. I can imagine that a small steel strip embedded in a stained glass panel would adequately attract a rare earth magnet without the problem of using two rare earth magnets in mutual attraction. But, you must select the magnet size so that the force to separate the magnet from the steel is not too large, or you will risk glass breakage. You can go to eBay and search for neodymium magnets and you will find a huge variety available. Buy some and play around. Strong magnets must be shipped in a steel container to contain the magnetic field. The post office gets quite upset if a package affects their equipment! Try dropping a cylindrical or spherical rare earth magnet down a copper tube. You'll be surprised at what happens, noting that copper is not ferromagnetic and is not at all attracted by the magnet. I have a physics demonstration apparatus I made using a 2-inch wide, 1/4-inch thick pure copper bar. I can roll a steel ball bearing down the strip without impediment; but a spherical rare earth magnet rolls down very slowly. Since the nickel plated rare earth magnet looks exactly like the ball bearing, some slight of hand makes this into an interesting demonstration piece. I offer this little essay just for its educational value! -- Best wishes, Larry McDavid W6FUB NASS Registrar Anaheim, CA (20 miles southeast of Los Angeles, near Disneyland) --- https://lists.uni-koeln.de/mailman/listinfo/sundial
