How could I get a copy of that article?
How could I get a copy of that article?
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The most direct way is to find a local Optometry school and ask to use the library. The easiest way is to go to your local library and fill out a form for an inter-library loan.
Opticiansfriend.com guy.
Harry, I am sending you an e-mail regarding this.Originally Posted by Harry
Darryl J. Meister, ABOM
I have tried working a problem out and can get the right answer when I do the left eye, but for some reason I keep making a mistake somewhere when I try to figure it out for the right.
problem being faceform and panto using Keatings article. Any suggestions?
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I'd just have to see your math. As you've probably noticed by now, the procedure for calculating combined tilt is considerably more involved than for calculating simple panto or wrap. Your mistake could be an order-of-operations issue, a sign convention issue, etcetera.Originally Posted by Harry
I'll give you a big hint for handling Keating's equations for right and left eyes, though: Ignore his conversions for the left eye, and simply change the wrap angle from positive to negative for the left lens. You'll get the same answer without having to use all of those additional equations to compensate for the left-eye coordinate system.
Lastly, all of these equations rely heavily on the dioptric power matrix. You should ensure that you've read that particular chapter in Keating's book thoroughly enough to understand what is happening (after all, you'll have to explain it, yourself, in your paper).
Darryl J. Meister, ABOM
I am going to review the article and tell you my first impressions on it (May take me a few days as I work all day tomorrow and have tons of other stuff to do to, but I'm really looking forward to it). I am pretty good at linear algebra etc.. so I don't believe I'll have a problem with the math just the initial setting up of the problem.
Opticiansfriend.com guy.
I got it. Whenever I do math that involves a few steps I always make errors. I will show you my answers following allong with the article
example -2.00 -3.00 x 25 panto=10 face=20 n=1.586
(same exact problem Darryl presented me with for just faceform)
Solving for the right eye
theta=22.27
Tc=1.22
Sc=1.05
Hc=1.13
A=27.27
theta sub A=-2.2732 -or- 177.73
new Rx on the tangential and sagital meridian of the eye
-2.00 -3.00 x 178
P sub x=-2.00
P sub y=-5.00
P sub t=-0.12
P" sub x=-1.64
P" sub y=-4.78
P" sub t=-0.11
t=-6.42
d=7.83
C"=-3.15
S"=-1.64
theta sub A"= 0
A"=25.51
theta"=25.51
compensated Rx is -1.64 -3.15 x 26
Thank you again Darryl the article and book are very informative. I totaly understand the part in the article where he has you switch the tangential and sagittal meridians by subtracting 90 degrees. I had a felling that their might be a better way that is why I was dead set in working the equation out using the right eye even though the article walks you step by step through the left eye with an example. I usually end up messing with numbers to check for patterns or easier ways of doing things. I guess this is what you did as well. I have a few more areas in optis I have not explored yet and am curious how many other equations can be applied to the power matrix? I will do more reading and post back.
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Basically, it occurred to me that if Keating's equations were indeed general enough (that is, if they would work with both positive and negative tilts without producing an ambiguous reference angle or something), you could replicate the performance of the left eye by simply changing the sign of the wrap angle. Since cylinder axis is prescribed using TABO notation, which means that the axis is measured counter-clockwise from 0 in both eyes, there is really no difference in power specification. Pantoscopic tilt also has the same coordinate system for both eyes. Further, since the left eye coordinate system for lens tilt basically represents a horizontally flipped right eye system, you could replicate a positive face-form wrap angle in the left eye by imaging a right eye with face-form wrap in the opposite direction (i.e., negative tilt). I double-checked the results and, indeed, I was correct, and this much simpler approach works just as well.Originally Posted by Harry
Darryl J. Meister, ABOM
That makes sense and simplifys the equation.
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Darryl, does your algorithm give the same result as exact ray-tracing would, even for tilt angles of 20-30deg?
I am asking this because I do agree with your approach to the subject and I wonder what the point to code all this when it seems like it is not less work then just to adjust some existing ray-tracing algorithm, isn't it?
For thin-ish lenses, it's actually quite close for the range of tilts that you are likely to see with a spectacle frame.Darryl, does your algorithm give the same result as exact ray-tracing would, even for tilt angles of 20-30deg?
If you have access to ray-tracing algorithms, and the capability to make such adjustments, No, you wouldn't need a program like this.I am asking this because I do agree with your approach to the subject and I wonder what the point to code all this when it seems like it is not less work then just to adjust some existing ray-tracing algorithm, isn't it?
Darryl J. Meister, ABOM
In KeaTings article he does mention that it is an approximation and that it losses accuracy at tilts of more than 30 degrees, but the likely hood of running into a frame with that much tilt is pretty slim and at that point it does give you a good approximation.
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"Of course" leave it too us great the "Italians" to develop a monomer with another chemical maker of whom will be not mentioned at this time, but it is also under experiment right now that this particular monomer will be available for Rx soon. Several sunglass companies now use it. NXT technology. From sources.
Sort of the same, since both Trivex and NXT can be made with different variations each, Trivex or NXT is not exactly the same. They can each make the material more or less flexible for example.
These are both products developed originally by Simula Technologies and they are both marketed under license from Simula.
NXT I think is restricted to plano and Trivex is restricted to prescription.
Last edited by AWTECH; 12-13-2005 at 02:14 PM.
Where can I find the copy of Keating's article that is referred? I have the latest copy of his book and would like to read this article. I looked on the Optometry and Vision Sciecne web site, but the archives do not go back that far.
Thanks in advance
Lensgrinder send me an e-mail and I WIll forward it to you.
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Hi Harry,
No i don't have it, could you please send it to me?
PM me your e-mail address.
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Add Heat Bend Lens,done.
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