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Thread: Optronics 3B Blocker Blackout

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    Optronics 3B Blocker Blackout

    I recently started working with an Optronics 3B blocker and have noticed difficulties blocking high minus and polarized lenses. For some reason the layout grid seems to blackout with polarized lenses similar to when polarized lenses are 90 degrees apart. With high minus lenses only the center lensometer mark is visible with the outer pin marks non visible. Is there an adjust I'm missing to be able to see lensometer marks, seg or progressive marking on polarized lenses?

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    Master OptiBoarder MakeOptics's Avatar
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    Quote Originally Posted by PRECISIONLAB View Post
    I recently started working with an Optronics 3B blocker and have noticed difficulties blocking high minus and polarized lenses. For some reason the layout grid seems to blackout with polarized lenses similar to when polarized lenses are 90 degrees apart. With high minus lenses only the center lensometer mark is visible with the outer pin marks non visible. Is there an adjust I'm missing to be able to see lensometer marks, seg or progressive marking on polarized lenses?
    The Briot Sanford used to have the same issue. According to Briot "nothing you can do". The issue was in the orientation of the LCD polarized filters.

    Here is my own solution, a wave retarder. Grab a sheet of 1/4 and 1/2 wave retarder and place them on the screen depending on your blockers orientation you will notice polarized light rotated enough to remove the blackout effect.

    As a side note some riki pads are optically active and can be used to similar effect. Place a few on the blocker and presto blackout gone. If you have optically active riki pads you can also layer them to increase the effect.
    http://www.opticians.cc

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    Where can we find either one of these items? We have an Eclipse blocker and get the same "nothing you can do" from Coburn.

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    with our 3B when we get tall minus we hold a plus 6.00 over the lens, this will bring up the lensometer dots so you can center. Easy Peasy!

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    Master OptiBoarder MakeOptics's Avatar
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    Quote Originally Posted by Opticianman View Post
    Where can we find either one of these items? We have an Eclipse blocker and get the same "nothing you can do" from Coburn.
    Edmund Optics - https://www.edmundoptics.com/optics/...retarder-film/

    They're about $10 for a sheet, I usually buy and keep on hand a 1/4 and a 1/2, you could technically layer 2 x 1/4 to get the 1/2 effect and the sheets are big enough to slit and still have a usable area for layout on your blocker but it looks a bit more amateur to have multiple layers. Added benefit they look and act like a screen protector, with 90% transmission then filter can be left on for all jobs without having any issues. As a caution they will throw off any autolensometry features in a blocker, usually causing axis values to be off, so remove them if you use an autoblocker, and manually block the polarized lenses.

    For high minus I like to keep a pen light next to the blocker and edge light the lens, this makes the marks more visible similar to how some LCD screens are edge lighted to brighten them display.
    http://www.opticians.cc

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