Laser Alignment: Is the Laser Perpendicular?

Discussion in 'Enlarging' started by ic-racer, Nov 23, 2008.

  1. ic-racer

    ic-racer Member

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    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.
    [​IMG]
     
    Last edited by a moderator: Nov 23, 2008
  2. Martin Aislabie

    Martin Aislabie Subscriber

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    Good explanation - and nice diagram too :D:D:D

    Martin
     
  3. ZoneIII

    ZoneIII Member

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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.
     
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  4. Lee L

    Lee L Member

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    I always do the same check on laser collimators for telescopes. Nicely presented.

    Lee
     
  5. dancqu

    dancqu Member

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    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. Neal

    Neal Subscriber

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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. L Gebhardt

    L Gebhardt Subscriber

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    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. ic-racer

    ic-racer Member

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    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. RJS

    RJS Member

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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. dancqu

    dancqu Member

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    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
     
  11. ic-racer

    ic-racer Member

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    That will align the negative stage to the baseboard, but, like on a view camera, lens tilt doesn't affect perspective. So your lensboard could still be out of alignment and it will still project a perfect geometric box. So you if you use that system, you also need to make sure all 4 corners of the box are sharp and in focus. Using the negative frame to assure good focus at the corners can be difficult because of its thickness. I have used a negative in the holder with the grain magnifier to ensure all 4 corners are sharp, thus confirming lensboard alignment. The grain magnifier that allows one to see the corners of the image cost almost double the laser device. I have both, though, so I can double check things.
     
  12. Martin Aislabie

    Martin Aislabie Subscriber

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    Fully agree with ic-racer.

    Like ic-racer, I have both the Laser and a Grain Magnifier which will see into the corners of the neg.

    I do a regular check on my enlarger with the grain magnifier to check that the corners and centre are in the same sharp focus.

    The grain magnifier is a quick way of telling you if everything is OK

    However, if itÂ’s not OK it wont help you put things right.

    Only the Laser will tell you which bit(s) have gone out of alignment

    Martin
     
  13. dancqu

    dancqu Member

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    So a square projected and still true on the baseboard
    assures that the planes of both the negative stage and
    baseboard are parallel.

    Now we introduce a tilt into the lens stage. The optical
    axis is not now perpendicular to the two parallel planes.
    Am I to believe that the tilting of the lens has no effect
    upon the shape of the projected image? No other effect
    than some out of focus condition?

    I've never had course to use Schleimpflug corrections
    when enlarging. With those one may, by tilting the lens
    correct for distortion in the negative. As I understand it
    the correction is a distortion of the negative's image
    upon the baseboard; a corrective distortion. So by
    a tilting of the lens a square at the negative stage
    may become a trapezoid or a parallelogram
    upon the baseboard. Dan
     
  14. Lee L

    Lee L Member

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    Yes.
    Correct.
    No. You have to tilt the easel relative to the negative to achieve the correction of keystoned perspective and make the parallel sides parallel again. Of course, this means that the plane of focus cuts through the easel/paper at some angle. The lens is then tilted to take advantage of the Scheimpflug principle in order to match the plane of focus to the plane of the easel/paper. You could also leave the easel on the plane of the baseboard and tilt the negative stage to correct for parallel lines, then tilt the lens to correct the plane of focus to match the baseboard according to the Scheimpflug principle.

    Lee
     
  15. dancqu

    dancqu Member

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    So a 'corrective distortion' of the negative's image is
    projected upon the baseboard. That 'distortion' applies
    to the entire negative or in my case the square of the
    negative carrier which I've used for alignment.

    From my reading this thread, if the projected image of
    a square is square but is not in focus upon the baseboard
    then the easel needs to be tilted.

    I believe I've correctly postulated although I should
    have emphasized SHARP as well as square.

    All this I've introduced is not to make alignment easy,
    laser or square. To paraphrase; The proof of the
    alignment is on the baseboard.

    Do any test for square? From the discussion
    I take it the projected image can be SHARP
    while not SQUARE. Dan
     
  16. ic-racer

    ic-racer Member

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    Yes, SHARP and SQUARE would confirm alignment.
     
  17. ic-racer

    ic-racer Member

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    Also, if your enlarger is aligned like this picture, all 4 corners of the image will be SHARP and in focus. (but your frame and image will be keystoned)

    [​IMG]