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  1. #1
    ic-racer's Avatar
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    Laser Alignment: Is the Laser Perpendicular?

    Since there were a few threads on enlarger alignment I thought I'd show this image that explains the how you can tell if your enlarger is out of alignment, or if your laser light is not perpendicular. The people that sell the laser light don't show you this because 'the laser light will always be perpendicular...'


    When you take you alignment reading, rotate the laser and watch the reflected beam.

    A) If the reflected beam stays centered on the target, this indicates the laser is perpendicular and the baseboard is parallel to the reflecting surface

    B) If the reflected beam is not on center and it does not move in relation to the enlarger as the laser is rotated, this indicates the laser beam IS perpendicular and the reflecting surface is NOT parallel to the baseboard.

    C) If the reflected beam is not on center and it follows the laser unit as it is rotated, that is, it always reflects back to the same point on the laser faceplate, this indicates that the laser beam is NOT perpendicular and the reflecting surface IS parallel to the baseboard.

    D) If the reflected beam is not on center and it follows the path of a circle with a center that does not rotate around with the laser faceplate, this indicates the laser beam is NOT perpendicular and the reflecting surface is NOT parallel to the baseboard. If you adjust the laser beam closer to parallel, the circular path of the beam gets smaller and smaller until it matches condition B. If you align the reflecting surface to be more parallel to the baseboard, the path of the beam will become concentric with the laser orifice and it will approach condition C.

    BOTTOM LINE: Good enlarger alignment can be indicated by both diagrams A and C below.
    Last edited by ic-racer; 11-22-2008 at 11:12 PM. Click to view previous post history.

  2. #2
    Martin Aislabie's Avatar
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    Good explanation - and nice diagram too

    Martin

  3. #3
    ZoneIII's Avatar
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    That's how I have always checked my own laser alignment tool out but your explanation goes further to describe the various possible conditions than I had thought of before. In fact, I'm going to print your excellent diagrams and post out for future reference and keep it in the box with my Versalab tool. Nice explanation! Thanks for posting. Very useful.
    Last edited by ZoneIII; 11-23-2008 at 05:15 PM. Click to view previous post history.

  4. #4
    Lee L's Avatar
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    I always do the same check on laser collimators for telescopes. Nicely presented.

    Lee

  5. #5

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    Quote Originally Posted by ic-racer View Post
    A) If the reflected beam stays centered on the target,
    this indicates the laser is perpendicular and the baseboard
    is parallel to the reflecting surface
    Questions from one who does not use a laser for alignment.
    Is that reflecting surface meant to be an exact substitute
    for the negative? Is it assumed that the negative and
    the reflecting surface occupy the same plane? Dan

  6. #6

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    Dear Dan,

    "Is that reflecting surface meant to be an exact substitute for the negative?"

    Essentially yes, but it can simply be parallel to the negative plane (e.g. place the reflector above the negative carrier assuming the carrier is flat).

    Neal Wydra

  7. #7
    L Gebhardt's Avatar
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    Is that reflecting surface meant to be an exact substitute
    You can also put the mirror in place of the lens to make sure the lens is aligned with the baseboard and the negative.

  8. #8
    ic-racer's Avatar
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    Quote Originally Posted by dancqu View Post
    Questions from one who does not use a laser for alignment.
    Is that reflecting surface meant to be an exact substitute
    for the negative? Is it assumed that the negative and
    the reflecting surface occupy the same plane? Dan
    Just to elaborate on what the others have pointed out.

    The IMPORTANT alignment is between LENS and NEGATIVE and the baseboard is not so critical (especially at high magnification). HOWEVER, there is no easy way to get the laser between the lens and the negative stage so the usual practice is to align negative stage (or carrier) to the baseboard, then align the lens to the baseboard. In general, a optical glass is used as the reflecting surface (like a microscope slide) and it is either positioned on the negative stage or carrier, or held on the front rim of the lens. In practice, I usually just put a glass negative carrier in the negative stage and reflect off of that.

    Just to elaborate on another technique I use; I have found the concentric rings of the diffraction pattern that occurs when the laser is pointed directly in to the center of the lens may be a better indication of lens centering than the front rim of the barrel. This is especially true on my 30mm Rokkor used for Minox and 16mm. The front of the lens barrel is the aperture ring, and it has a little wobble in it.

  9. #9
    RJS
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    To add a slight bit of additional confusion to the discussion. Versalab includes instructions on resetting the alignment of the laser so it is exactly perpendicular to the base board. As described by IC Racer (sp?). Versalab also instructs using a rubber band to hold a piece of glass (it appears to be a microscope slide) to the barrel of the lens (Michael Mouse I think thought this up for them). My hands no longer being as clever as they were at one time I decided to use a screw in filter on the enlarging lens with a bit of paper stuck to the upper side. Ctein, in his fine book discusses the concentricity of the lens barrel with the lens elements - he found it was quite good. However, I found that a really cheapo filter didn't seem to have the glass concentric with the ring, so I tried a B&W filter I haven't been using. There was a significant difference. I emailed Versalab with this wonderful information and they responded they didn't think so. Didn't say why.

    So there is my contribution to the great dancing angels controversy!

  10. #10

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    Quote Originally Posted by ic-racer View Post
    Just to elaborate on another technique ...
    Yet another technique:

    Just suppose or postulate that if a projected image
    is in form the exact of some object projected then
    we can say within our context that the system
    is aligned.

    Based upon that postulate I've aligned my enlarger
    using the square of the negative carrier as the object
    for projection. At the baseboard I employ a square to
    assure 90 degree agreement.

    That's it. Of course the image need be well focused
    for accurate use of the square. An object truly square
    but smaller than the negative carrier could be the
    subject for alignment. Dan

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