 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Medical Forum / General / Vision / September 2007Accurately measuring dioptre of specs
I have a dozen pairs of ready-made reading glasses. Most of them no longer have the strength of the lenses marked on them. I do recall that they were originally marked to within 0.25 dioptre. How can I work out the dioptre value of each pair using home equipment? >I have a dozen pairs of ready-made reading glasses. > > Most of them no longer have the strength of the lenses marked on them. > I do recall that they were originally marked to within 0.25 dioptre. > > How can I work out the dioptre value of each pair using home equipment? dont need any. just hold the lens close and move it slowly away from you till you get a blur circle, take that distance and devide it by one meter. 1 dioptre is one meter. 2 dioptre is at 1/2 meter Blur circle is when the image in the lense has blured to a constant value across the lens, no image remains. > I have a dozen pairs of ready-made reading glasses. > > Most of them no longer have the strength of the lenses marked on them. > I do recall that they were originally marked to within 0.25 dioptre. > > How can I work out the dioptre value of each pair using home equipment? By what mechanism do you propose the lenses changed their curvatures or refractive indices? Short of cooking in an oven even plastic lenses will remain constant over centuries of time. Do you open your cupboard to find cheap plastic film drinking cups have deformed? Plastic lenses are thicker and stiffer.  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 [snip drool] -- 'we establish by definition that the "time" required by light to travel from A to B equals the "time" it requires to travel from B to A' because I SAY SO and you have to agree because I'm the great genius, STOOOPID, don't you dare question it. -- Rabbi Albert Einstein http://www.androcles01.pwp.blueyonder.co.uk/Smart/tAB=tBA.gif 'we establish by definition that the "time" required by light to travel from A to B doesn't equal the "time" it requires to travel from B to A in the stationary system, obviously.' -- Heretic Jan Bielawski, assistant light-bulb changer. Ref: news:1188363019.673281.67710@k79g2000hse.googlegroups.com "SR is GR with G=0." -- Uncle Stooopid. The Uncle Stooopid doctrine: http://sound.westhost.com/counterfeit.jpg "What can be asserted without evidence can also be dismissed without evidence." -- Uncle Stooopid. "Counterfactual assumptions yield nonsense. If such a thing were actually observed, reliably and reproducibly, then relativity would immediately need a major overhaul if not a complete replacement." -- Humpty Roberts. Rabbi Albert Einstein in 1895 failed an examination that would have allowed him to study for a diploma as an electrical engineer at the Eidgenössische Technische Hochschule in Zurich (couldn't even pass the SATs). According to Phuckwit Duck it was geography and history that Einstein failed on, as if Eidgenössische Technische Hochschule would give a damn. That tells you the lengths these lying bastards will go to to protect their tin god, but its always a laugh when they slip up. Trolls, the lot of them. "This is PHYSICS, not math or logic, and "proof" is completely irrelevant." -- Humpty Roberts. >> I have a dozen pairs of ready-made reading glasses. >> [quoted text clipped - 10 lines] > open your cupboard to find cheap plastic film drinking cups have > deformed? Plastic lenses are thicker and stiffer. The lenses have not changed their dioptre value! Apologies if I did not make this clear .... Originally there was a some writing on the reading glasses which stated the dioptre value of the lenses. This has has been rubbed off. I want to establish what is the dipotre value of any particular pair of reading glasses. > >> I have a dozen pairs of ready-made reading glasses. > [quoted text clipped - 20 lines] > I want to establish what is the dipotre value of any particular pair > of reading glasses. Well, ODs can do it just looking on glasses or putting them on with rather good precision. > > By what mechanism do you propose the lenses changed their > > curvatures or refractive indices? Short of cooking in an oven even > > plastic lenses will remain constant over centuries of time. Do you > > open your cupboard to find cheap plastic film drinking cups have > > deformed? Plastic lenses are thicker and stiffer. > The lenses have not changed their dioptre value! Apologies if I did > not make this clear .... [quoted text clipped - 5 lines] > I want to establish what is the dipotre value of any particular pair > of reading glasses. CRIPES! Do NOT apologize to Uncle Al. The guy really knows how to write and lie with words, but unfortunately hasn't learned how to read them yet! The rest of us knew exactly what you were saying. It was completely clear. By the way if you want an accurate measurement of Diopter values take your box of glasses to any place that sells glasses (prescription glasses not a drugstore) and they will have a machine to do it. It sort of looks like an overgrown microscope. You put the glasses in the bottom and there is this large wheel on the side you turn graduated in diopters. Works like a champ. By the way, in trying to use the "focusing the sun on a piece of paper" method, be informed that the paper will likely catch fire! > CRIPES! Do NOT apologize to Uncle Al. The guy really knows how to > write and lie with words, but unfortunately hasn't learned how to read > them yet! The rest of us knew exactly what you were saying. It was > completely clear. Every NG has its own Otis Brown, eh? Sorry.... > By the way, in trying to use the "focusing the sun on a piece of > paper" method, be informed that the paper will likely catch fire! I watched my father do this. It seemed to work. There was little chance of a fire. The circles were quite large. I doubt that an OTC reading glass could cause a fire. > In article <1189329571.509620.220...@50g2000hsm.googlegroups.com>, > [quoted text clipped - 4 lines] > chance of a fire. The circles were quite large. I doubt that an OTC > reading glass To be precise " reading PLASTIC" Regards, > To be precise " reading PLASTIC" I don't think it matters plastic or glass. All that matters is flux, and flux goes up with diameter and down with warpage and so forth. If it's a contest, I'm pretty sure you could find OTC glasses big enough to gather flux and focus it to something resembling a point. -MT > > To be precise " reading PLASTIC" > [quoted text clipped - 5 lines] > > -MT Well. ok Lena. Dear Lena, Subject: Using a reading glasses to ignite paper. In the prosses of determining focal length, I testes quite a few reading-glasses. I could not get the paper to ignite. Using a 4 inch magnifying glass (with a 20 inch focal length) concentrated enough flux on a point to ignite the paper. Best, Otis > > > To be precise " reading PLASTIC" > [quoted text clipped - 8 lines] > Well. ok > Lena. On Sep 13, 5:21 am, "otisbr...@pa.net" <otisbr...@pa.net> wrote: > Dear Lena, > > Subject: Using a reading glasses to ignite paper. > > In the prosses of determining focal length, I testes quite > a few reading-glasses. 1) Your spelling sucks. Too many meds? Too few meds? 2) If you spent LESS TIME playing with your testes, you might have better vision now. OTOH, if you spent MORE TIME playing with your testes, you might not hurt people on s.m.v. anymore. Either way, talking about this with a woman online makes you an unabashed pervert (in addition to your default status as a pathological liar and a f.cking idiot). Dear Winke, Subject: The physics of a plus lens -- optical power The power of a lens is given in diopters. The relationship is: Diopters = 1 / Focal-length For instance, a focal length of 0.5 meters will have a power of 2 diotpers. The easy way, is to just take the lens outdoors, and hold it above a paper. If the lens forms an image of the sun at 0.5 meters -- the power is 2 diopters. If at 1 meter, the power is 1 diopter. Simple as PI. Best, Otis > I have a dozen pairs of ready-made reading glasses. > > Most of them no longer have the strength of the lenses marked on them. > I do recall that they were originally marked to within 0.25 dioptre. > > How can I work out the dioptre value of each pair using home equipment? > How can I work out the dioptre value of each pair using home equipment? the only reasonable way using home equipment is exactly as described by Otis' reply to your message a couple of days ago. go outside, hold the lens up at the height that results in a sharp point focus of the sun, measure that distance in meters, and then calculate the dioptric power. dioptric power = reciprocal of the focal distance measured in meters. opticians and eye doctors use an apparatus called a lensometer to precisely measure lens power. there are other ways as well, such as trial lens neutralization, etc. but these require a little more than "home equipment". : > How can I work out the dioptre value of each pair using home equipment? : : the only reasonable way using home equipment is exactly as described : by Otis' reply to your message a couple of days ago. go outside, hold : the lens up at the height that results in a sharp point focus of the : sun, Doesn't work for concave lenses. >:> How can I work out the dioptre value of each pair using home equipment? >: [quoted text clipped - 4 lines] > > Doesn't work for concave lenses. Reading glasses - which the OP was talking about - are not concave. So what is your point? SignatureNicolaas. ... Some people post not because they have something to say, but because the have to say something .... anything. : >:> How can I work out the dioptre value of each pair using home equipment? : >: [quoted text clipped - 7 lines] : Reading glasses - which the OP was talking about - are not concave. : So what is your point? Mine are, although I read without them in bed, book 6" from my nose. For the computer monitor, concave. So what is your point, idiot? : >:> How can I work out the dioptre value of each pair using home equipment? : >: [quoted text clipped - 7 lines] : Reading glasses - which the OP was talking about - are not concave. : So what is your point? Mine are, although I read without them when in bed, book 6"- 9" from my nose. For the computer monitor I wear concave lenses, for driving I have varifocals. Doesn't work for concave lenses, imbecile. So what is your point, fuckhead? Subject: PClar is correct. The original poster asked only about plus lenses. Not a minus lens. If you are curious, just hold a minus lens above a sheet of paper. Now slowly lift the minus lens off the paper. The light will "spread" -- and no image can be formed. It would be possible to obtain some low-cost minus lenses from Zennioptical.com for about $5 for each one. What Pclar was referring to was the fact that a +2 diopter lens can be neutralized by a -2 lens. For thin lenses the powers "add" when they are close together. Just basic science and optical physics. Otis On Sep 9, 12:26 pm, p.clar...@gmail.com wrote: > > How can I work out the dioptre value of each pair using home equipment? > [quoted text clipped - 10 lines] > there are other ways as well, such as trial lens neutralization, etc. > but these require a little more than "home equipment". > For thin lenses the powers "add" when they are close > together. > > Just basic science and optical physics. And also why people working with lenses use "diopters" Note that if you have a positive lens with a known diopter value that is stronger than the negative lens, if you put the two together it will form an image that focuses and you can measure the diopters of the combo. Hence by the above rule you can find the diopters of the negative lens. > otisbr...@pa.net wrote: > [quoted text clipped - 10 lines] > the combo. Hence by the above rule you can find the diopters of the > negative lens. Yes, certainly ,it is the rule how Mystery of minus lens was resolved. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.