jacman Posted June 30, 2003 Report Posted June 30, 2003 hey kids... can anyone guess what my avatar is, and what it is used for? if so i'll snail-mail you a cool prize. jacman Quote
JSngry Posted June 30, 2003 Report Posted June 30, 2003 It ALMOST looks like one of those old turntable strobe discs you used to check the table's speed, but I don't think that's what it is. Quote
brownie Posted June 30, 2003 Report Posted June 30, 2003 It's a bird'es eyeview of a lampshade... Quote
Son-of-a-Weizen Posted June 30, 2003 Report Posted June 30, 2003 The pupil-constricted eye of one of those Thai 'sea gypsy' children who can see clearly underwater? Quote
catesta Posted June 30, 2003 Report Posted June 30, 2003 Looks like the exhaust trail from a 1949 Desoto. B) Quote
J Larsen Posted June 30, 2003 Report Posted June 30, 2003 (edited) It looks just like Newton's rings from a lens in contact with a plane glass surface. The distance between fringes gives a measure of the precsion of the lens being tested. I'd go in to a little more detail, but I'm really busy right now! (In fact, I'm so busy I half-botched this the first time I posted, hence the edit!) Edit 2: Okay, as I have a second here and there I may add a bit to this post I said above that Newton's rings are often used for examining the quality of a lens. Another application is examining the quality of a thin film. If you have a lens of known precision (say, one wavelength of red light, which is very realistic for a quality lens), then the rings can reveal imperfections in the smoothness of the thin film. Another edit: It also looks like the diffraction pattern you get if you carefully aim a high-quality laser at a metal sphere, so that the laser beam is perfectly perpendicular to the surface of the sphere. It is very tricky to get this exactly right! I did this demonstration for a class I taught a year ago. In the morning section it worked perfectly. I spent less than 15 seconds adjusting the laser to get the diffraction pattern. In the mid-day section I struggled with it for over five minutes before giving up. I don't think the mid-day students ever believed that it should really work! It is really strange the first time you see it, as normally you only get the center fringe and then it appears that the laser light is going directly through the metal sphere. Edited June 30, 2003 by J Larsen Quote
connoisseur series500 Posted June 30, 2003 Report Posted June 30, 2003 It's a bulls-eye burned into the furniture as a result of one of Charlie Parker's cigarette butts. Quote
Jazzmoose Posted June 30, 2003 Report Posted June 30, 2003 I don't know what it is, but after staring at it for a couple of minutes, I have to go watch the 700 club and get my daily instructions from brother Pat... Quote
Templejazz Posted June 30, 2003 Report Posted June 30, 2003 A close-up of the center of an LP as the grooves come closer together? either that or..... " The wheels on the bus go round' an round' " Quote
jacman Posted July 1, 2003 Author Report Posted July 1, 2003 to all of the above posts...nope. interesting guesses tho. Quote
JazzKitten Posted July 1, 2003 Report Posted July 1, 2003 (edited) Bird's eye view of a grooved drinking glass? JK P.S. Actually, I think I've once seen a lighthouse light that kind of looks like that from the side. HUGE panes of glass. Is that what it is? Edited July 1, 2003 by JazzKitten Quote
J Larsen Posted July 1, 2003 Report Posted July 1, 2003 (edited) An example of Newton's rings: I believe these rings were actually produced by placing two glass films on top of each other. Edited July 1, 2003 by J Larsen Quote
Use3D Posted July 1, 2003 Report Posted July 1, 2003 I think it's an optical illusion. The circles are consentric but they appear to produce a square shape. Maybe. It's a guess. Edit: Upon resizing the picture the square shape vanishes. It's a result of the compression. Boo me. Quote
J Larsen Posted July 1, 2003 Report Posted July 1, 2003 Here's a picture of the diffraction of a laser around a metal sphere. The effect is MUCH more impressive when you see it in person, as it then appears that the light goes right through the sphere. This is actually a pretty lousy photo. I'll replace it with a better one if I can find one. Quote
jacman Posted July 1, 2003 Author Report Posted July 1, 2003 (edited) wow-ya'll are some right smart folks. but, i'm afraid the guesses so far are incorrect. here's a hint: it has something to do with the photographic arts. Edited July 1, 2003 by jacman Quote
J Larsen Posted July 1, 2003 Report Posted July 1, 2003 Well, they do use the Newton's rings phenomenon at Kodak to ensure the quality of photographic film, and at all lens factories to ensure lens precision, but I guess you have something else in mind. Do you use that thing for light metering or contrast adjustment? Quote
jacman Posted July 1, 2003 Author Report Posted July 1, 2003 it has nothing to do with a camera lens...other than it is anti-lens... it is a Zone Plate. used in leu of a camera lens, the circles are alternating opaque non-opaque redering the subject very soft focused. (from the web): i'm a pinhole camera photographer (aspiring pro) and i'm experimenting with zone plates. the avatar is a huge blow-up, in real life they are very small. average aperture is about f/100. so, J Larsen wins the prize (if you wanna call it a prize)! i'm getting back my first set of pix taken with my homemade zone plate camera...J Larsen will win a print or three. PM sent Quote
catesta Posted July 2, 2003 Report Posted July 2, 2003 it has something to do with the photographic arts. Ah Ha! It's a picture of the exhaust trail from a 49 Desoto. Dang...., you gave the answer already didn't you. Quote
J Larsen Posted July 2, 2003 Report Posted July 2, 2003 I like to thank all the little posters who helped me along the way in winning this prize. jacman, do you have any pictures of your pinhole camera that you can post? I had my students make their own in a class I taught a couple years ago. They seemed to get a kick out of it. Quote
jacman Posted July 2, 2003 Author Report Posted July 2, 2003 here's a Santa Barbra Lensless Camera. i have 3, 4x5s (varying focal lengths) and a 5x7. i also have a super wide angle pinhole (4X5). sorry no pic. my zoneplate camera is an old cheap Russian made "Lubitel TLR". i removed the shutter and lens, mounted the zoneplate on a piece of shim stock in which i punched a small hole, and mounted that into the shutter mount. took about 10 minutes time. Quote
Bright Moments Posted February 22, 2004 Report Posted February 22, 2004 hey kids... can anyone guess what my avatar is, and what it is used for? if so i'll snail-mail you a cool prize. jacman my guess is they are drums. used to make music. what's my prize jacman? Quote
BERIGAN Posted February 22, 2004 Report Posted February 22, 2004 Psst, Larsen...quick...post again, anything!!!! J Larsen Posted: Jun 30 2003, 11:51 AM Supa Groover Group: Members Posts: 666 Member No.: 70 Joined: 7-March 03 Location: Manhattan Quote
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