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Thread: Any trick to center a lens exactly in the middle?

  1. #1
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    Default Any trick to center a lens exactly in the middle?

    I just made my first diode housing myself.
    Milled a hole of 8,50 mm and then tapped with m9x0.5 with a tap adapter so it goes in straight.
    After that i fitted in my lens (glass broadband lens in plastic barrel from o-like)
    But now it seems to have some space, i can feel it moving a little bit.
    When i rotate the lens i can see the dot getting smaller but also moving in circles out of the center (on a distance of 15 meter)

    Is there any trick to fill up this unwanted space between the m9x0.5 hole and the lens so that it will stay exactly on the same spot at 15 meter but only gets smaller / bigger
    My guess is it is around 0,05 to 0,10 mm to fill up.

  2. #2
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    The lenses are almost never perfectly centered in the mounts. So most people move around the diode in the mount, to center it to the lens.

  3. #3
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    White Teflon plumbing tape on barrel thread .
    Cheers

  4. #4
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    The usual trick for concentric and parallel diode lasers involves two pinholes spaced a meter apart on a sliding rail, a four quadrant detector and a precision holder to rotate the laser barrel, which looks like a metalworking lathe in construction. There are other tricks involving pentaprisms, CCD cameras with no lens, etc.. The diode is held at the back by a compression plate on screws so it can slide around. None of these things are cheap..

    Which means, Teflon Tape for most amateurs.

    Steve
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  5. #5
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    I love your answers.

    Quote Originally Posted by mixedgas View Post
    The usual trick for concentric and parallel diode lasers involves two pinholes spaced a meter apart on a sliding rail, a four quadrant detector and a precision holder to rotate the laser barrel, which looks like a metalworking lathe in construction. There are other tricks involving pentaprisms, CCD cameras with no lens, etc.. The diode is held at the back by a compression plate on screws so it can slide around. None of these things are cheap..

    Which means, Teflon Tape for most amateurs.

    Steve

  6. #6
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    Thanks! will use teflon tape for this one but i don't like it so much.
    Think for the next housing that i make i will get a threadmill and make the m9x0.5 a bit undersize so that there is less space left between the lens and the m9 hole

    off-topic: is the only advantage of brass over aluminium that it has better heat transfer?

  7. #7
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    Quote Originally Posted by laserjohnn View Post
    Think for the next housing that i make i will get a threadmill and make the m9x0.5 a bit undersize so that there is less space left between the lens and the m9 hole
    Just FYI, collimation lenses vary a bit in their thread depths. G2 lenses sold by DTR tend to be looser in most of the brass mounts I have purchased (requiring teflon tape) while the G2 lenses sold by Aixiz (AixiZ Multi-Band AR Lens 400-700nm single element G2 (AD-9GL-MFL)) are very tight in brass mounts like those sold by Dave at Lasershowparts.

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

  8. #8
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    @ "off-topic: is the only advantage of brass over aluminium that it has better heat transfer? "

    Aluminium is also a lot lighter which becomes important with very high powers (lots of components) also design must take "creep" into account!
    (normally almost impossible to detect).But there are very many different qualities of aluminium and the lowest quality is not very uniform which means expansion/contraction is non-linear. Brass has a higher coefficient of expansion but is very uniform! even compared to good quality aluminium.

    So it's really down to availability/price and whether you prefer silver colour to gold colour (although coloured diode holders in anodized ally are available now from "lasertack" a forum member.
    I am currently waiting on a couple to test them.

    Cheers
    Last edited by catalanjo; 09-30-2015 at 05:00.

  9. #9
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    Aluminum has about twice the thermal conductivity of brass. Both materials machine pretty easily with edge going to brass. Copper conducts twice as well as aluminum. It is awful to machine.

    The problem with centering the lens can have several sources. The use of Teflon (polyethylene impregnated with PTFE) tape is not a bad thing. The gaps created by a loose thread fit can be variably filled with the tape and it will tend to cause the barrel to self center. Also, aluminum does not work well with aluminum. The interface galls easily and the tape prevents this. In addition, the lens may have a clearance fit and when retained by the ring, it may not rest coaxial with the barrel. Finally, the lens may even have a manufacturing decentration as well.

  10. #10
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    I love the answers you guys post. Teflon tape is my solution. Not too much though.
    This space for rent.

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