Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,951   Posts: 1,585,997   Online: 791
      
Page 2 of 2 FirstFirst 12
Results 11 to 17 of 17
  1. #11
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,396
    Quote Originally Posted by dancqu View Post
    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
    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.

  2. #12
    Martin Aislabie's Avatar
    Join Date
    Nov 2007
    Location
    Stratford-upon-Avon, England
    Shooter
    4x5 Format
    Posts
    1,413
    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 it’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

  3. #13

    Join Date
    Sep 2002
    Location
    Willamette Valley, Oregon
    Shooter
    Medium Format
    Posts
    3,684
    Quote Originally Posted by ic-racer View Post
    "That will align the negative stage to the baseboard, ..."
    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

  4. #14
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    Quote Originally Posted by dancqu View Post
    So a square projected and still true on the baseboard
    assures that the planes of both the negative stage and
    baseboard are parallel.
    Yes.
    Quote Originally Posted by dancqu View Post
    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?
    Correct.
    Quote Originally Posted by dancqu View Post
    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
    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

  5. #15

    Join Date
    Sep 2002
    Location
    Willamette Valley, Oregon
    Shooter
    Medium Format
    Posts
    3,684
    Quote Originally Posted by Lee L View Post
    You have to tilt the easel relative to the negative to
    achieve the correction of keystoned perspective and
    make the parallel sides parallel again. ... The lens is
    then tilted ... in order to match the plane of focus
    to the plane of the easel/paper.
    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

  6. #16
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,396
    Quote Originally Posted by dancqu View Post
    I believe I've correctly postulated although I should
    have emphasized SHARP as well as square.
    Yes, SHARP and SQUARE would confirm alignment.

  7. #17
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,396
    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)


Page 2 of 2 FirstFirst 12


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin