Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 68,770   Posts: 1,484,282   Online: 1156
      
Page 1 of 2 12 LastLast
Results 1 to 10 of 12
  1. #1
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    7,481

    Finding optical center of a lens

    What practical way apt for a home workshop is there to find the optical center of a given spectacle lens.

  2. #2
    Greg Davis's Avatar
    Join Date
    Feb 2004
    Location
    Crestview Hills, KY
    Shooter
    8x10 Format
    Posts
    1,869
    In the optical industry we use something called a Vertometer, also called an Optometer. It shows the power of the lens and the optical center. Any place that makes prescription glasses will have one.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  3. #3
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    7,481
    Of course I thought of the optician in town. But, as I am considering the use of cheap plastic lenses a DIY approach would be more appropriate.

  4. #4

    Join Date
    Mar 2013
    Location
    rAdelaide
    Shooter
    Multi Format
    Posts
    733
    Is this for lens-building (centre of element), or for panoramic-stitching (centre of lens)?

    For Panos there's always the DIY way, which is just keep taking shots and rotating and making sure they line up with no parallax (possible on film, but a lot cheaper with more recently-invented technology).

    For finding the centre of an element, maybe you could do the same thing? Depends if you need precision to within a few mm, or a few microns.
    An awful lot of electrons were terribly inconvenienced in the making of this post.

  5. #5
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    7,481
    It is for lens building. More precise for diopter modification. Plastic spectacle lenses are not only cheap but also easy to cut.

    I just remembered that spectacle frames often show the center distance. Thus the easiest way I guess would be just to take that figure, center it and cross it with half of the lens vertical diameter, to get somewhere near the center of the lenses...
    Last edited by AgX; 04-09-2014 at 07:01 PM. Click to view previous post history.

  6. #6
    Greg Davis's Avatar
    Join Date
    Feb 2004
    Location
    Crestview Hills, KY
    Shooter
    8x10 Format
    Posts
    1,869
    Just be aware that as the lenses get stronger, any misplacement of the center will become more aggressive. For example, as per the Prentice Rule, if a 1 diopter lens is off center by 1cm, it will be off power by one diopter. A 2 diopter lens will be off by one diopter if it is only 0.5cm decentered, and a 4 diopter lens will be off power by one diopter if it is decentered by only 2.5mm.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  7. #7
    ath
    ath is offline
    ath's Avatar
    Join Date
    Aug 2006
    Location
    Germany
    Shooter
    35mm
    Posts
    885
    The Vertometer is called "Scheitelbrechwertmesser" in german and completed auctions on ebay Germany start at about 50€.
    If I would start lens assembly I would buy one.
    Regards,
    Andreas

  8. #8

    Join Date
    Jan 2004
    Location
    NYC
    Shooter
    Medium Format
    Posts
    1,154
    Curious... I took a closer look at my prescription glasses n found the centers of the lenses also seems to be the thinest part of the lens.... Of course assuming the center would cooincide with where my pupils seem to align as center to center.
    Anyone can make a Digital print, but only a photographer can make a photograph.

  9. #9
    Greg Davis's Avatar
    Join Date
    Feb 2004
    Location
    Crestview Hills, KY
    Shooter
    8x10 Format
    Posts
    1,869
    If you have a minus prescription, then the optical center should be in the thinnest part of the lens. Conversely, a plus prescription should be in the thickest, however, sometimes the lenses are made to shift the center to correct for other vision problems. Bifocals get more complicated.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  10. #10
    AgX
    AgX is offline

    Join Date
    Apr 2007
    Location
    Germany
    Shooter
    Multi Format
    Posts
    7,481
    Yes, I also thought of measuring the lens thickness. I am interested in positive menisci. Thus I would have to fix a tiny sphere to one of the ends of a micrometer caliper. Something well in the range of a DIY workplace.

Page 1 of 2 12 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin