Page 2 of 2 FirstFirst 12
Results 26 to 35 of 35

Thread: Lens thickness & fitted back vertex distance

  1. #26
    Master OptiBoarder MakeOptics's Avatar
    Join Date
    Aug 2011
    Location
    none
    Occupation
    Other Eyecare-Related Field
    Posts
    1,327
    Quote Originally Posted by Robert Martellaro View Post
    “In response to poor fitting in the form of tilt or decentration, lenses with aspheric form surfaces were found to have greater off-axis power errors than best-form lenses with spherical surfaces.” -Atchison, D. A. & Tame

    https://www.ncbi.nlm.nih.gov/pubmed/8278198


    https://www.opticianonline.net/news/...lar-refraction

    https://www.odob.health.nz/wp-conten...f-D-Wilson.pdf
    Nailed it, best form base curves can be estimated with vogels rule, thats where plus 6 comes from it's the guesstimated optimal back curve. demo lenses have a curvature to which you can clock, it comes out to being close enough to what the actual back curve is, then as Brent so eloquently put it the power error is negligible from there.
    http://www.opticians.cc

    Creator of the industries 1st HTML5 Browser based tracer software.
    Creator of the industries 1st Mac tracer software.
    Creator of the industries 1st Linux tracer software.

  2. #27
    Master OptiBoarder MakeOptics's Avatar
    Join Date
    Aug 2011
    Location
    none
    Occupation
    Other Eyecare-Related Field
    Posts
    1,327
    Since I'm no longer in the field I can give one of my best vertex measuring device secrets away. Take a simple PR ruler with see through windows (you know the ones that sit on the bridge and have a window that measures the PD's), get a Fresnel prism 25D (or any two Fresnel prisms that add up to 50D, 25 is simple because you only have to use one and cut two pieces, but a 10 and 40, or 20 and 30, etc. will work). Cut the prism into 2 pieces and place them so that the lines are oriented vertically to match the hash marks on the windows on the PD ruler, but only cover the top half of the window leave the bottom of the window clear, place the other piece on the back side of the ruler over the top of the window with their base in the opposite direction. This now adds up to 50D of prism in the top half of the window. Now the difference between top and bottom is 50D of prism. Since prism diopters measure a deviation of 1cm over a distance of 1m and 100cm go into a m you can hold the PD ruler to the front of the frame (with demo lenses out) and bisect the pupil with the top and bottom half of the prism line, the distance in mm between them * 2 is the vertex distance. You would be surprised how accurate this is and the measure is to the front plane of the specs, so if you want to get super nerdy you can caliper the frames for the distance to the bevel from the front and subtract that out and now you have the exact measure to a useful reference point. The bevels can be placed and measured, the back sag can be measured so you can add/subtract away all these measures to come to a accurate measure, of course it's a bit much.
    http://www.opticians.cc

    Creator of the industries 1st HTML5 Browser based tracer software.
    Creator of the industries 1st Mac tracer software.
    Creator of the industries 1st Linux tracer software.

  3. #28
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,385
    MO, what field are you in, now?

  4. #29
    Master OptiBoarder optical24/7's Avatar
    Join Date
    May 2006
    Location
    Down on the Farm
    Occupation
    Dispensing Optician
    Posts
    5,809
    Quote Originally Posted by MakeOptics View Post
    Since I'm no longer in the field.... .
    I feel like Darryl just died again...But good luck MO in your new career...

  5. #30
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,385
    I remember seeing a picture of a "prismatic doublet" vertexometer online (from Rodenstock?) that I always coveted but never could obtain.

    Now I can build my own!

    Much appreciated.

    Glad you hang out here, occasionally MOHC.

    I'm going to use a corneal reflex. Maybe I'll post a pic.

  6. #31
    One eye sees, the other feels OptiBoard Silver Supporter
    Join Date
    Jul 2002
    Location
    Wauwatosa Wi
    Occupation
    Dispensing Optician
    Posts
    5,458
    Quote Originally Posted by drk View Post
    I remember seeing a picture of a "prismatic doublet" vertexometer online (from Rodenstock?) that I always coveted but never could obtain.
    Yes, Rodenstock made two versions. Pictured, with instructions, on page 6 and 7 of the David Wilson link above. Prof. Wilson used to post on Optiboard.

    Harry, I hope your having fun and getting paid for it.

    Best regards,

    Robert Martellaro
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



  7. #32
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,385
    I didn't open that, before.

    That's a killer resource.

    Hey...I smell a thread nomination.

  8. #33
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    When I’m faced with a real VD/power compensation in Rxs say, > -11.00D, and a fitted VD out if the norm—say 8-9mm measured with a VD caliper and no known refractive VD—I will order some cheap 1.74 lenses and glaze the chosen frame.

    Then I call back the patient, fit these, and over refract to obtain best acuity. Then this becomes the ordered Rx.

    Small price and effort to pay to ensure the absolute best vision when I’m fitting $1k+ premium FF progressives.

    And of course, they always say “No one’s ever done that before.”

    B

  9. #34
    What's up? drk's Avatar
    Join Date
    Mar 2004
    Location
    Ohio
    Occupation
    Optometrist
    Posts
    9,385
    Wouldn't it save a lot of time and money to do that in a trial frame?

  10. #35
    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
    Join Date
    May 2000
    Location
    Seaford, NY USA
    Occupation
    Dispensing Optician
    Posts
    6,008
    Nope

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Vertex distance & population statitstics
    By Hayde in forum General Optics and Eyecare Discussion Forum
    Replies: 8
    Last Post: 09-08-2017, 07:49 PM
  2. vertex distance
    By chaoticneutral in forum General Optics and Eyecare Discussion Forum
    Replies: 21
    Last Post: 07-11-2014, 01:06 PM
  3. what is back vertex distance?
    By The Revolution in forum Ophthalmic Optics
    Replies: 2
    Last Post: 12-04-2012, 05:47 PM
  4. vertex distance with a free form lens
    By eyeoneder in forum General Optics and Eyecare Discussion Forum
    Replies: 2
    Last Post: 12-09-2010, 12:43 AM
  5. Vertex Distance and what would you do question.
    By hip chic in forum General Optics and Eyecare Discussion Forum
    Replies: 11
    Last Post: 01-30-2006, 03:30 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
  •