Results 1 to 17 of 17

Thread: 2nd year is here!

  1. #1
    OptiBoard Apprentice
    Join Date
    Jan 2007
    Location
    Ireland
    Occupation
    Lens Manufacturer
    Posts
    19

    2nd year is here!

    Hello all,

    well some of yous might remember me from last year and my endevours to pass First year of a long distance learning course to become a optical technician. Well i passed somehow! and onto second year.


    I am onto paper 5 and got 2 questions.

    Q1.
    Rx +2.50/-5.50x180 is decentered 8mm up and in along 60 before the right eye. Calculate the single resultant prism produced by this decentration.



    Don't answer it for me, i just cant understand what the question is asking, is it saying the lens is decentered 8mm up and 8mm IN, if this is the case whats the 60 for?
    or
    the lens is decentered 8mm up and the resultant prism is along 60?

    GAH!!


    Q2. Most bi-focal lenses have the reading addition in the segment. Can you name a solid bifocal that has the distance Rx in the segment?

    To put it honestly no i cant name one, any of yous know one?




    Thanks in advance!
    Del

  2. #2
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    Quote Originally Posted by Del View Post
    Hello all,

    well some of yous might remember me from last year and my endevours to pass First year of a long distance learning course to become a optical technician. Well i passed somehow! and onto second year.


    I am onto paper 5 and got 2 questions.

    Q1.
    Rx +2.50/-5.50x180 is decentered 8mm up and in along 60 before the right eye. Calculate the single resultant prism produced by this decentration.



    Don't answer it for me, i just cant understand what the question is asking, is it saying the lens is decentered 8mm up and 8mm IN, if this is the case whats the 60 for?
    or
    the lens is decentered 8mm up and the resultant prism is along 60?

    GAH!!


    Q2. Most bi-focal lenses have the reading addition in the segment. Can you name a solid bifocal that has the distance Rx in the segment?

    To put it honestly no i cant name one, any of yous know one?




    Thanks in advance!
    Del
    Q1 I am assumeing they mean it's decentered along the 60 8mm, the up and in sounds like a clue as to which way it is decentered. If you were to find the power along the 60o meridian than you would have a power to plug into prentices rule.

    S60 = +2.50 + -5.50 * sin2(60)
    S60 = +2.50 + -5.50 * 0.75
    S60 = +2.50 + -4.12
    S60 = +1.62

    P60 = 1.62 * 0.8
    P60 = 1.30

    Q2 I have never heard of a lens with the distance in the seg, but can name a PAL similar to what you are asking, the Definity has Ground View Technology, whihc is a fancy way of saying the power starts to go back towards the distance. Hope that helps, I will look into any other lenses that might exhibit this distance in the segment. It might be specific to your side of the pond though.
    Last edited by HarryChiling; 10-24-2007 at 05:31 PM. Reason: obxeyeguy caught a mistake
    1st* HTML5 Tracer Software
    1st Mac Compatible Tracer Software
    1st Linux Compatible Tracer Software

    *Dave at OptiVision has a web based tracer integration package that's awesome.

  3. #3
    Master OptiBoarder
    Join Date
    Feb 2007
    Location
    NC
    Occupation
    Dispensing Optician
    Posts
    3,951
    P60 = 1.62 * 0.08
    P60 = 0.13

    Harry, help me. I agree with the power calculation at 60, but a +1.62 moved 8mm causes more prism than an 1/8th. My simple prentice rule= +1.62 x 8 =12.96 divided by 10 = 1.29

  4. #4
    Master OptiBoarder
    Join Date
    Aug 2007
    Location
    Ontario, Canada
    Occupation
    Dispensing Optician
    Posts
    982
    I've never heard of a lens with the distance in the seg... let alone a a situation where you would NEED something like that o_o

  5. #5
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    Quote Originally Posted by obxeyeguy View Post
    Harry, help me. I agree with the power calculation at 60, but a +1.62 moved 8mm causes more prism than an 1/8th. My simple prentice rule= +1.62 x 8 =12.96 divided by 10 = 1.29
    Thanks for the edit, your right.:hammer: You old timers are good for something (as I duck and cover) :D
    1st* HTML5 Tracer Software
    1st Mac Compatible Tracer Software
    1st Linux Compatible Tracer Software

    *Dave at OptiVision has a web based tracer integration package that's awesome.

  6. #6
    Master OptiBoarder
    Join Date
    Feb 2007
    Location
    NC
    Occupation
    Dispensing Optician
    Posts
    3,951
    You old timers are good for something (as I duck and cover) :D
    :cheers:

  7. #7
    Banned
    Join Date
    Dec 2006
    Location
    On Top
    Occupation
    Other Eyecare-Related Field
    Posts
    1,662
    Quote Originally Posted by Del View Post
    Hello all,




    Don't answer it for me, i just cant understand what the question is asking, is it saying the lens is decentered 8mm up and 8mm IN, if this is the case whats the 60 for?
    or
    the lens is decentered 8mm up and the resultant prism is along 60?


    Del
    I know what you mean. We used to have customers order like this and we always called to make sure. I am not going to say what they usually ment to ask for because I think the answer would be different. I'd would answer both ways with an explanation.

  8. #8
    Master OptiBoarder lensgrinder's Avatar
    Join Date
    Jul 2005
    Location
    Raleigh, NC
    Occupation
    Lens Manufacturer
    Posts
    504
    OK here is the way I would figure it.

    He stated 8mm up and in @ 60 so we need to resolve this to find out how much vertical and horizontal decentration there is, because 8mm is like the hypotenuse of a right triangle.








    So you are decentering the lens 4mm in and 6.9mm up. Now figure your prism vertically and horizontally.







    Now use Pythagoras's Theorem to find the resultant prism



  9. #9
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    Quote Originally Posted by lensgrinder View Post
    OK here is the way I would figure it.

    He stated 8mm up and in @ 60 so we need to resolve this to find out how much vertical and horizontal decentration there is, because 8mm is like the hypotenuse of a right triangle.








    So you are decentering the lens 4mm in and 6.9mm up. Now figure your prism vertically and horizontally.







    Now use Pythagoras's Theorem to find the resultant prism


    I thought of doing it that way as well, but thought it should have worked out just using the power along the meridian the same, obviously it didn't where do the two cross? Interesting.
    1st* HTML5 Tracer Software
    1st Mac Compatible Tracer Software
    1st Linux Compatible Tracer Software

    *Dave at OptiVision has a web based tracer integration package that's awesome.

  10. #10
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    Question #2 - Rede Rite, has a small distance portion in the upper part of the lens. I had to dig deep for that one.
    1st* HTML5 Tracer Software
    1st Mac Compatible Tracer Software
    1st Linux Compatible Tracer Software

    *Dave at OptiVision has a web based tracer integration package that's awesome.

  11. #11
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    Question #2 - Rede Rite, has a small distance portion in the upper part of the lens.
    Yes, it was basically a reverse Ultex bifocal...
    Darryl J. Meister, ABOM

  12. #12
    Master OptiBoarder Darryl Meister's Avatar
    Join Date
    May 2000
    Location
    Kansas City, Kansas, United States
    Occupation
    Lens Manufacturer
    Posts
    3,700
    Rx +2.50/-5.50x180 is decentered 8mm up and in along 60 before the right eye. Calculate the single resultant prism produced by this decentration
    The question is asking about a lens decentered obliquely along the 60-degree meridian, which would represent the upper nasal quadrant in the right eye (i.e., "up and in," which was indicated just to clarify the decentration direction). Since the principal meridians correspond with the X and Y axes of decentration, once you have resolved the decentration at axis 60 into horizontal and vertical components, you can use the calculations that Lensgrinder provided. If the cylinder had been at an oblique axis, however, the mathematics become more complicated. In any case, you can also verify your calculations at OptiCampus Induced Prism Calculator.
    Darryl J. Meister, ABOM

  13. #13
    OptiBoard Apprentice
    Join Date
    Jan 2007
    Location
    Ireland
    Occupation
    Lens Manufacturer
    Posts
    19

    thanks

    Thanks for all the help guys!

    I will post what the instructor says when he returns my homework in a weeks time!

  14. #14
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    I am still a little curious why the power on the 60 didn't work out accurately? Is it becasue the equation for the power on the 60 is done using a formula that is exponetial where the seperate meridians are linear? Or am I just in left field with this one?
    1st* HTML5 Tracer Software
    1st Mac Compatible Tracer Software
    1st Linux Compatible Tracer Software

    *Dave at OptiVision has a web based tracer integration package that's awesome.

  15. #15
    Master OptiBoarder lensgrinder's Avatar
    Join Date
    Jul 2005
    Location
    Raleigh, NC
    Occupation
    Lens Manufacturer
    Posts
    504
    Quote Originally Posted by HarryChiling View Post
    I am still a little curious why the power on the 60 didn't work out accurately? Is it becasue the equation for the power on the 60 is done using a formula that is exponetial where the seperate meridians are linear? Or am I just in left field with this one?
    Harry, as you know when you move a lens obliquely it will cause different amounts of prism vertically and horizontally. Because it was 8mm @ 60 this will cause a certain amount of prism horizontally and a certain amount vertically in which case you need to find the result of those two put together.
    It is like saying I moved this lens 4mm in and 7mm up the result was 8mm, but this caused 2^ vertically and 1^ horizontally the result of which is 2.3^.
    You cannot take 0.8 X the power @ 60 because the net effect is different in each meridian.

    I hope this sheds some light on your question.

  16. #16
    Master OptiBoarder
    Join Date
    Feb 2007
    Location
    NC
    Occupation
    Dispensing Optician
    Posts
    3,951
    I hope this sheds some light on your question.
    It does here to old and slow. Took me drawing out your first explanation to get it.

  17. #17
    ATO Member HarryChiling's Avatar
    Join Date
    Apr 2005
    Location
    Nowhereville
    Occupation
    Other Eyecare-Related Field
    Posts
    7,765
    Quote Originally Posted by lensgrinder View Post
    Harry, as you know when you move a lens obliquely it will cause different amounts of prism vertically and horizontally. Because it was 8mm @ 60 this will cause a certain amount of prism horizontally and a certain amount vertically in which case you need to find the result of those two put together.
    It is like saying I moved this lens 4mm in and 7mm up the result was 8mm, but this caused 2^ vertically and 1^ horizontally the result of which is 2.3^.
    You cannot take 0.8 X the power @ 60 because the net effect is different in each meridian.

    I hope this sheds some light on your question.
    Thanks Brent, I had a feeling you would shed some light on this. When I think about it it makes total sense, I actually recently on a thread warned someone of this very same short cut and did it myself.:hammer: That's why I have you guys my collective optical brain. :D
    1st* HTML5 Tracer Software
    1st Mac Compatible Tracer Software
    1st Linux Compatible Tracer Software

    *Dave at OptiVision has a web based tracer integration package that's awesome.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Rep of the Year
    By Johns in forum General Optics and Eyecare Discussion Forum
    Replies: 6
    Last Post: 02-24-2003, 07:03 PM
  2. The Next Year
    By John R in forum General Optics and Eyecare Discussion Forum
    Replies: 4
    Last Post: 01-29-2003, 02:50 AM
  3. Man of the Year
    By Dot the Eye in forum General Optics and Eyecare Discussion Forum
    Replies: 23
    Last Post: 11-16-2002, 03:37 PM
  4. New Year Greetings..
    By Optom in forum Just Conversation
    Replies: 8
    Last Post: 01-02-2002, 08:52 AM
  5. New Year
    By Maria in forum Just Conversation
    Replies: 12
    Last Post: 01-02-2001, 02:35 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •