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Thread: distance between cylindrical lenses?

  1. #1
    Join Date
    Jun 2017
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    Default distance between cylindrical lenses?

    I saw a template on this forum with different arrangements of prisms for getting different magnification, but I can't find something similar for cylindrical lenses. Of course just a distance between lenses : magnification amount chart would do.
    I got some 4x cylindricals.
    Thanks for your time.

  2. #2
    Join Date
    Feb 2007
    Location
    Fort Mill, SC USA
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    Default

    Consider reaching out to CDBEAM here on the forum. He's kept track of how to correct several diodes with cylindrical lenses and frequently shared this information. I tried digging through his posts over the past few years, but I couldn't find what I was looking for.

    -David
    "Help, help, I'm being repressed!"

  3. #3
    Join Date
    Nov 2010
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    346

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    The distance is always fixed, you can not change the magnification for them. "4x" refers to magnification for a particular pair of lenses

    To find the distance between the lenses, you must calculate the sum of the back/effective focal length of both lenses, for "4X" pair this values is usually 25mm and -6.25mm, so you should get about 18.75mm

  4. #4
    Join Date
    Jun 2017
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    thanks. stupid question, distance between which points of the lenses? Center of the lenses, 'front' and back sides?

  5. #5
    Join Date
    Nov 2010
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    346

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    mmm ... if you know BFL, then use this value. EFL is not counted from the geometrically central point and where this point is located, you can find at the lens datasheet.
    But such an accurate calculation usually does not make sense, since any lenses (especially chinese) has some variations in their specs. You need to be able to focus them manually within +/- 1-2mm of the calculated value

  6. #6
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    Jun 2017
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    Sorry still don't get it, 18.75mm you got is from where to where? front surface of the first lens to the back surface of the second lens?

    But such an accurate calculation usually does not make sense, since any lenses (especially chinese) has some variations in their specs. You need to be able to focus them manually within +/- 1-2mm of the calculated value
    You mean compensate imperfect distances between the cylindrical lenses by the distance between the emitter and collimator lens?

  7. #7
    Join Date
    Nov 2010
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    I don't know what you bought )) 18.75mm for EFL points and only for above lenses.

    In laser optics, in most cases the same rules apply as in classical optics. Telescope and collimator are two unrelated systems. First you need to focus the beam, then expand it with a telescope, if needed. The telescope (distance between two lenses) is adjusted regardless of the distance from the collimator
    You mean compensate imperfect distances between the cylindrical lenses by the distance between the emitter and collimator lens?
    When you get them and make a couple of tests, you will understand everything.

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