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Thread: Find the optical center

  1. #1
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    Find the optical center

    This is taken from another thread I posted in and didnít get any responses. The thread was complaining
    about the lack of training and understanding being exhibited by many of todayís opticians.
    letís see how many answers I get to this question. I have used this in the past about 25% knew the answer.
    which of the following items can you use to find the optical center on a lens the two lenses in the list are not the lens you have to find the center

    1 pencil
    2 marking pen
    3 piece of paper
    4 +1.00 sph
    5 -1.00. Sph
    6 caliper
    7 microscope
    8 mm scale

    After you select the items needed how would you proceed

  2. #2
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    I'm a remnant of the late 70's Coburn 108 generator days. I used a caliper to determine center thickness via edge thickness around various points on the block. Prism either ground for decentration or unwanted could also be checked via a caliper @ the principle meridians while still blocked.

    For OC location use caliper to determine thickest for plus power or thinnest point for minus on the lens
    Last edited by PRECISIONLAB; 09-23-2022 at 05:34 AM.

  3. #3
    What's up? drk's Avatar
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    I'll take the marking pen approach.

    Look through the lens at a vertical line (like a doorframe) and align the doorframe image through the lens with the doorframe view outside the lens. Draw the doorframe image with a marker, top to bottom.

    Look through the lens at a horizontal line (like the edge of a desk) and align the desk edge image through the lens with the desk edge view inside the lens. Draw the desk edge image with a marker, side to side.

    The intersection of the two lines is the optical center.


    WHAT DO I WIN!!!!!! A box of optical centers????

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    Before I give my answer although there might be other ways to do this I will tell you about a device I have that you can’t even find a mention of it on the internet. It is probably circa 1900 made by American Optical called
    a lens centering device. The set up is something like a lensometer but no light and all open. There is an engraved target with a cross on it that can rotated with degree markings and it had a marker like a lensometer. You moved the lens until the lines on the cross were continuous both horizontally and vertically and you can align the cylinder axis as well then you marked it. This is as accurate as a lensometer but no power readings. How you did that we will save for another day.

    the prize for the closest answer is a box of candy coated optical centers very hard to come by.

  6. #6
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    There might be more than one correct answer this is mine. Answer to Chris you surely don’t need all the items. A caliper that is generally used in ophthalmic optics is not accurate enough to find the thickest or thinnest point on a lens unless it was mounted in a fixture a dial indicator would work but marking the lens would difficult if was made with that in mind it could produce a good result.
    DRK has an idea similar to mine but it would be difficult to draw a thin line across the lens two times without even 1 mm of error maybe if you are really talented you could get good results. That earns half a bag of candy coated optical centers.
    here is my answer take the paper and the mm scale and draw a cross that is at least 10 mm larger than the lens in x and y axis. Hold the lens about 15 mm above the cross and move it until both lines on the cross are continuous then take a marker and spot the of the cross on the lens. Check results by holding the lens above the cross lining dot with center making sure the cross is not broken. Ask people you work with to try this it will start a conversation about optics that will help all of your staff.

  7. #7
    What's up? drk's Avatar
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    Oooo I like it.

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