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Thread: Penlight, my new best friend.

  1. #1
    ATO Member HarryChiling's Avatar
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    Penlight, my new best friend.

    I just had neutralize a pair of low vision specs that would not read in my lensometer with a penlight. Suprisingly it didn't take very long (15 min) and I was accurate to within 0.75D. I just wanted to toot my own horn real quick, back to business.

    Fezz, about that beer slide .. . ...
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  2. #2
    Master OptiBoarder
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    You Got Gusto Man!

    Look at you. Job well done!

    I'll check with management. I think we may be able to get you a couple freebie rides on the slide for a job well done.

    Bravo man...!

  3. #3
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    Just think back to the very old days when we didn't have lensometers and everthing had to be neutralized with a lens bench.

  4. #4
    ATO Member OPTIDONN's Avatar
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    I'm just lazy. We got this antique lensometer that has a slot for prism rings or trial lenses. Persons like a +30.00 or something crazy just pop in a -15.00 trial lens knocks it down to a readable amount. If I put in a -15.00 trial lens and get a +15.00 reading I know it's a +30.00.

  5. #5
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    Harry, how does one go about hand neutralizing via penlight? Why didn't it read in your lensometer (low vision specs...power too high, too much prism)?
    I learned about hand neutralizing with a set of known lenses and obverving motion, but how does the penlight come in?
    Your humble student asks for more info!

  6. #6
    Master OptiBoarder rbaker's Avatar
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    We used to do clinics at the nut house and had to neutralize with trial lenses. After about ten hours you could do it as accurately as with a lensometer. Its also good practice for retinoscopy, but we don’t do that anymore, do we?

    Pen light or muscle light and PD rule, still the gold standard for measuring PD’s.

  7. #7
    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by EyeFitWell
    Harry, how does one go about hand neutralizing via penlight? Why didn't it read in your lensometer (low vision specs...power too high, too much prism)?
    I learned about hand neutralizing with a set of known lenses and obverving motion, but how does the penlight come in?
    Your humble student asks for more info!
    It wouldn't read in the lensmeter, because it had too much prism. 21 BI OU so I couldn't get the mires to even come into view in my lensmeter. The power ended up being +16.00DS 21BI OU, if you are interested in finding out how it is done check out Brent's article on ray tracing.

    http://onlineopticianry.com/wordpress/?p=108

    For the prism I just laid out a mark on the floor 1 meter from a wall, shinned the penlight onto the wall placed a mark at the center of the light, then placed the lens in the path of the light and again marked the spot on the wall. Took the measure of the displacement in cm and whalla you have the prism.

    The power was just as simple, except I would move the penlight and glasses untill I had a focused spot on the wall and then leave them on the floor in the same spot where they came in to focus then measure the distance from the penlight to the glasses, and the measure from the glasses to the wall.

    1/Power = 1/Image - 1/Object
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