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Thread: Take a Master Exam

  1. #76
    OptiWizard
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    Quote Originally Posted by optical24/7 View Post
    So, does this rule only work with flat tops? Wonder if I was doing a Franklin bifocal with a -2.00 dist/+2.00 add? I would be using a -2.00 for dist and a Plano for near. How am I going to decenter the plano's OC enough to get 1d of prism?

    I'm really sorry guys. I hear what you are saying to think of the seg as it's own little lens, but in my minds lensometer, it's not seeing it!
    it works for all bifocals, even round segs.

    remember, bifocals are basically a smaller lens fused into a larger lens.

    In a -2.00 DS OU, +2.00 add

    yes the total power in the segment is Plano, but you are not placing the segment oc directly in front of the eye.

    Also,
    Just because the total power is Plano in the segment, does not mean you cannot acheive prism.

    A perfect example is the clip example I used above.

    or how about this,
    if you put on -2.00 sph contacts, then put on a pair of +2.00 readers.
    would you need to take a PD measurement?
    Or does PD not matter?

  2. #77
    Master OptiBoarder optical24/7's Avatar
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    Forgive an old man's brain. Well, your +2.00 reader has power. You displace the OC from the normal PD and you can create a prismatic error. How do I move a plano's OC to create 1D of prism without grinding it in?

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    I think the issue is we are not talking about two separate lenses in reality? Of course if you take say a 1 base in prism in front of contacts the image will enter the first lens and exit then enter the contacts with said end result and travel theoretically without prism due to the contact moving with the eye while converging. But this is not the case with eyeglass lenses. We are talking about a image that is entering and exiting "one" lens.
    We or most I hope agree with what a separate +2.50add will do if moved said mm. But that's really not what were talking about. We could talk math all day long and not put our math to use, our math is only as good as the end result of said math so lets put our math to the test on Monday? If your interested to know if "your" math works cut or order problem #15 with "C" being the answer and see what you get and then post your result here for the world to see. I am by no means at the level of most optically, just a guy that has the hands of someone who is twenty years my senior.

    15. Given the following FT-35 bifocal prescription:
    +2.00 DS with a +2.50 D add, O.U. (both eyes)
    PD’s = 66/62 mm
    How could you induce a 1
    D base in prismatic effect, per eye, at near only?
    a. Use a 56 mm distance PD
    b. Use a 60 mm near PD
    c. Use a 54 mm near PD
    d. Can’t be done
    Ok so everybody is clear we've got a PT with a PD of 66/62 were going to grind or order depending on our situation 66/54. Cut, edge and mount said lens and neutralize the end result. Display your finding here and we'll go from there?
    Game anybody?

  4. #79
    ABOM Wes's Avatar
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    Quote Originally Posted by optical24/7 View Post
    Forgive an old man's brain. Well, your +2.00 reader has power.
    So does a +2.00 seg.

    Quote Originally Posted by optical24/7 View Post
    You displace the OC from the normal PD and you can create a prismatic error. How do I move a plano's OC to create 1D of prism without grinding it in?
    It's not plano. The seg has power.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  5. #80
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    Quote Originally Posted by optical24/7 View Post
    So, does this rule only work with flat tops? Wonder if I was doing a Franklin bifocal with a -2.00 dist/+2.00 add? I would be using a -2.00 for dist and a Plano for near. How am I going to decenter the plano's OC enough to get 1d of prism?

    I'm really sorry guys. I hear what you are saying to think of the seg as it's own little lens, but in my minds lensometer, it's not seeing it!
    An old style Franklin actually was 2 lenses. However, in this example, you couldn't decenter the lower half of the lens, because it actually would be plano, but most times that wouldn't be the case, and you could use decentration.. But, in your example, you'd have to grind the prism into it, and glue it to the top.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  6. #81
    ABOM Wes's Avatar
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    Quote Originally Posted by King.Matthew View Post
    I will recheck it tomorrow in the lab, have you done this in actual glasses or just in math? A Dr. I used to work for would request base in prism in the near about 2 times a week on our older patients and I would always calculate it out using the distance Rx in connection with the Add power? I guess I could have been doing it wrong but the results using my method always portrayed the end result I wanted. I guess I would say don't take my word for it, try it in your lab tomorrow and see what you get? I would be interested to know what your lab equipment does with the Rx of +2.00 with an Add of +2.50 and the PD 66/54?
    I've done it many times in the lab. I now work for an LMS software company and help others do it. The math is solid. I'll type up an example of a rather difficult one I helped one of our lab customers with a little later. Gotta run.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

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    Quote Originally Posted by Wes View Post
    An old style Franklin actually was 2 lenses. However, in this example, you couldn't decenter the lower half of the lens, because it actually would be plano, but most times that wouldn't be the case, and you could use decentration.. But, in your example, you'd have to grind the prism into it, and glue it to the top.
    But I thought the "little add" has no dependance on the "distance" Rx? The thread has stated that regardless of the distance you only calculate the power of the add for decentration?

  8. #83
    Master OptiBoarder optical24/7's Avatar
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    Quote Originally Posted by Wes View Post
    An old style Franklin actually was 2 lenses. However, in this example, you couldn't decenter the lower half of the lens, because it actually would be plano, but most times that wouldn't be the case, and you could use decentration.. But, in your example, you'd have to grind the prism into it, and glue it to the top.
    This is exactly what I am talking about. This formula does not work for all scenario's, or at least all types of bifocals. If the formula doesn't work for a Franklin, how does it work in a ft35 if the segmented area is nutrilized down to Plano? In a lensometer, can you see the OC move when you view it across the segments area (Plano)?

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    Quote Originally Posted by Wes View Post
    I've done it many times in the lab. I now work for an LMS software company and help others do it. The math is solid. I'll type up an example of a rather difficult one I helped one of our lab customers with a little later. Gotta run.
    How difficult can it get when your only considering the add?

  10. #85
    ABOM Wes's Avatar
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    Matt said:We or most I hope agree with what a separate +2.50add will do if moved said mm. But that's really not what were talking about.

    That is exactly what we are talking about.

    Matt said:
    We could talk math all day long and not put our math to use, our math is only as good as the end result of said math so lets put our math to the test on Monday? If your interested to know if "your" math works cut or order problem #15 with "C" being the answer and see what you get and then post your result here for the world to see.

    My math? The math has been around far longer than I. I am just a user of the technique.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  11. #86
    ABOM Wes's Avatar
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    Quote Originally Posted by King.Matthew View Post
    But I thought the "little add" has no dependance on the "distance" Rx? The thread has stated that regardless of the distance you only calculate the power of the add for decentration?
    Apples and oranges.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  12. #87
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    Quote Originally Posted by optical24/7 View Post
    This is exactly what I am talking about. This formula does not work for all scenario's, or at least all types of bifocals. If the formula doesn't work for a Franklin, how does it work in a ft35 if the segmented area is nutrilized down to Plano? In a lensometer, can you see the OC move when you view it across the segments area (Plano)?
    I never said it would work in every scenario. Someone else said that. With a ft-28, the seg is superimposed over the carrier. With a Franklin, the seg is its own lens. Apples and oranges.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  13. #88
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    Quote Originally Posted by Wes View Post
    Apples and oranges.
    Apples and orange trees continue to produce apples and oranges? If I get a grape fruit from one of the trees I would have to rename the tree?

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    Master OptiBoarder optical24/7's Avatar
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    Wes, I never doubt you're knowledge. You're one of the smartest guys around on technical optical stuff. I'm sure you and others are right. I'm just having a hard time understanding how the total power of the segmented area has no bearing on how much you would decenter, only the amount of add.

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    Quote Originally Posted by Wes View Post
    I never said it would work in every scenario. Someone else said that. With a ft-28, the seg is superimposed over the carrier. With a Franklin, the seg is its own lens. Apples and oranges.
    I am only talking about problem #15 of the review test here? I had issue with "C" being the correct answer and wanted some clarification as I did not agree with it? I cut it and did not get what "C" said I should get, end of story. I am asking you as I'm sure working for a LMS software company would have a test lab and could generate said scenario, and show that "C" is correct, not by math, because what would it matter if the math said this is the result but the glasses measured said no its not?

  16. #91
    ABOM Wes's Avatar
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    Quote Originally Posted by King.Matthew View Post
    How difficult can it get when your only considering the add?
    Imagine a pt DPD of 73, NPD 70. +2.25 add. Distance Rx irrelevant. Doc needs 3 diopters base in OU at near. Use ft-45. Each seg needs to be decentered 13.3 mm from 70, for a total inset of 14.8 mm. Lab software only allowed 5 each eye, for a total of 10. We amended the sf lens data from seg inset 5 in to 4.8 out the get the extra 9.8mm required to meet Rx. Worked like a charm.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  17. #92
    ABOM Wes's Avatar
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    Quote Originally Posted by King.Matthew View Post
    I am only talking about problem #15 of the review test here? I had issue with "C" being the correct answer and wanted some clarification as I did not agree with it? I cut it and did not get what "C" said I should get, end of story. I am asking you as I'm sure working for a LMS software company would have a test lab and could generate said scenario, and show that "C" is correct, not by math, because what would it matter if the math said this is the result but the glasses measured said no its not?
    I have already done this, many times, myself. Please see above example as the most recent occurrence of helping someone else do it. I'm not going to ask someone to do it again for no reason other than to satisfy you. I'm sorry, but you made some kind of mistake in your procedure or in your reading.

    The reason math works, is because it represents reality. If it didn't, it would be useless, and there would be no technology, and no civilization past the hunter-gatherer level.

    To add: this practice exam was put together by the brilliant Darryl Meister, ABOM(RIP) and has been vetted for years. It's not likely to be proven incorrect today.
    Last edited by Wes; 07-25-2015 at 08:53 AM.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  18. #93
    Master OptiBoarder optical24/7's Avatar
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    Once again Wes, I'm sure you are correct. But as I asked earlier, if the segmented area is Plano due to Rx, would you see the near OC move as you moved it horizontally in a lensometer? Once again, forgive me my friend, I'm just having a dickens of a time wrapping my brain around this!

  19. #94
    ABOM Wes's Avatar
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    Quote Originally Posted by optical24/7 View Post
    Once again Wes, I'm sure you are correct. But as I asked earlier, if the segmented area is Plano due to Rx, would you see the near OC move as you moved it horizontally in a lensometer? Once again, forgive me my friend, I'm just having a dickens of a time wrapping my brain around this!
    Assuming your earlier Rx of -2, +2 add. Assume near pd of 62. If you decentered the seg 5mm and read the near power at 62 mm, you would see plano with 1 diopter prism, base in. Remember, you aren't moving the distance OC. The seg has an OC and power of its own. 5 mm away from the OC of a +2 lens, how much prism do you see? Conversely, in your Franklin example, using -2 dist, +2 add, the lower portion would indeed be plano. That's not the case with a "carried" seg like a ft.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  20. #95
    Master OptiBoarder optical24/7's Avatar
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    Ok, I'm starting to visualize that. I'm still gonna order me a ft like above so I can see it myself!�

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    Quote Originally Posted by Wes View Post
    I have already done this, many times, myself. Please see above example as the most recent occurrence of helping someone else do it. I'm not going to ask someone to do it again for no reason other than to satisfy you. I'm sorry, but you made some kind of mistake in your procedure or in your reading.

    The reason math works, is because it represents reality. If it didn't, it would be useless, and there would be no technology, and no civilization past the hunter-gatherer level.

    To add: this practice exam was put together by the brilliant Darryl Meister, ABOM(RIP) and has been vetted for years. It's not likely to be proven incorrect today.
    I am by no means trying to prove somebody that is obviously ten times more knowledgeable than I am wrong. But I will add if we continue down a path that our predecessors had it right and we do not will only limit us in furthering our knowledge. They are a foundation to build upon?!
    I have an electrical engineering degree and can assure you that math and reality are two separate things. I can build a circuit board using 3D software that allows me to plug and play if you will with resistors, gates, capacitors, you name it and have it run perfectly in a perfect world, and then build a live model and promise you it will not work "correctly". There will need to be tweaking done after the fact because lets face it, we do not live in a perfect world.
    Could I have done something wrong in my mock test of problem 15? Of course, will I run another test and do it again from scratch to see what I get of course I will. I only ask that somebody else do it as well because if they get what I get then "C" is wrong!
    Do you run test's after software is created to see if the end result is what was expected? Of course you do, why?
    I by no means am trying to argue a point, I just need 2+2 to equal 4.
    At the end of the day if said answer will be "C" on the ABO Advanced Test then that will be what I will pick. Easy enough.

  22. #97
    ABOM Wes's Avatar
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    We don't live in a perfect world, and we don't manufacture to exact specs. We manufacture to tolerances. In your circuit board example, sometimes the parts weren't manufactured to tolerances, or perhaps, tolerances add up. Also, quantum physics and relativity must come into play with very small distances found in microprocessors and the time dilation that affects GPS, respectively, for example.
    But that's not really the case in our situation. The question at hand is old hat in this industry, proven thousands of times over.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

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    Quote Originally Posted by Wes View Post
    We don't live in a perfect world, and we don't manufacture to exact specs. We manufacture to tolerances. In your circuit board example, sometimes the parts weren't manufactured to tolerances, or perhaps, tolerances add up. Also, quantum physics and relativity must come into play with very small distances found in microprocessors and the time dilation that affects GPS, respectively, for example.
    But that's not really the case in our situation. The question at hand is old hat in this industry, proven thousands of times over.
    I guess the only question I would have is a Ft-35 add power super imposed as stated over the carrier or is it one lens? if one lens then personally I would think the image path only encounters two surfaces and thus the thickness "apex to base" of said lens has to be considered ultimately resulting from distance and add Rx, if in fact the lens is "super imposed" then there would be four surfaces the image would be traveling through front and rear of add lens then front and rear of distance lens.
    As I learn more I'm sure I or somebody else will prove me wrong, I am ever learning and ultimately do not want to be right, just want to have the right knowledge.

  24. #99
    ABOM Wes's Avatar
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    There are obviously only two surfaces in question on a molded plastic ft35. The word superimposed was used to try to explain the thinking that solves the question, primarily because nothing else had worked to explain it to that point.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

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  25. #100
    OptiWizard
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    Sorry for the confusion, when you said franklin bofocal, I assumed you meant executive bifocal(old habits die hard).


    you don't need to surface anything to prove the math.

    Easiest way is to take two FSV lenses with opposing powers(i.e. +1.00 ds and -1.00 ds)

    Put them back to back, total power of plano.
    If you moved them together in a lensmeter there should be no prism induced.
    But if you move one separately from another, it will behave like a +/- 1.00 DS in terms of prism

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