Vexing Alignment, Easel Issue

Discussion in 'Enlarging' started by jeroldharter, Mar 31, 2009.

  1. jeroldharter

    jeroldharter Member

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    I am getting really annoyed with alignment. I have a Beseler 45 VXL enlarger. I verified that the lens stage, negative stage and baseboard are in alignment. As I drilled down through possibilities, I figured out that my easel is bowed. In fact, they all are. I have 3 Saunders Pro 4 blade easels:11x14, 16x20, and 20x24. All of them are convex on the surface with the center of the easel slightly closer to the lens than the corners of the easel.

    For 8x10 and 11x14 prints the problem is small. But for 16x20 the problem is unacceptable. I'm not sure what to do about it. I do have a vacuum easel that I have never used. I pulled that out but it has 4 leveling feet which I can never seem to get right but the center of it (steel plate) seems slightly bowed as well. Is it just me? Any advice is appreciated.
     
  2. Stew

    Stew Member

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    Would closing the lens down to a smaller aperture help?
     
  3. bdial

    bdial Subscriber

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    For the vacuum easel, it may well have some bow built-in so that it is flat when operating.
    On the others you may be able to tweak them flatter by carefully applying some force in strategic places. Though it seems odd that all of them are distorted.
    Do you have an accurate straightedge to judge the flatness?
     
  4. ic-racer

    ic-racer Member

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    What is exactly the problem? (blurry on one corner, two corners, all corners?) What format? What negative carrier? What lens?

    Something to consider is that bigger the magnification the less your baseboard/easel flatness matters. Also, as magnification increases, the more your negative to lens alignment matters.

    For a 16x20 from 35mm negative, one side of the easel can be up in the air 2 inches and it should still be in focus.

    So, it is possible that the easel is not the culprit.
    Are you sure the negative is held flat?
    Is the negative centered on the image circle (flatness of field will diminish at the periphery of the image circle)?
     
    Last edited by a moderator: Mar 31, 2009
  5. ic-racer

    ic-racer Member

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    Perhaps. You can use the view camera focusing method with an enlarger. Jeff Conrad derived some equations that allow you to figure the maximum tolerable F number based on the MTF (personal correspondence).

    N_max ~ 20 / (1 + m) sqrt(dv)

    N_max = maximum tolerable F number
    m = magnification
    dv = distance on the enlarger column between good focus on the highest and lowest portions of the curved or askew negative. (if 'dv' is zero then your negative is not curved or enlarger/baseboard/easel is not askew)

    I'm curious as to what your 'dv' is. In terms of 4x5, I find that it is just a few millimeters, as the 4x5 film tends to hold pretty flat even in a glassless carrier. If you are using 4x5 and you get more than a few millimeters for 'dv' then something is amiss, though stopping down may help.
     
  6. TimVermont

    TimVermont Subscriber

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    My vacuum easel is "crowned" when not in use, but is as flat as I can measure when in use and a sheet of paper is in place. A very small rubber machinist's mallet, a dial indicator and a surface plate may be what you need to deal with your easels. After reading this: http://www.horolezec.cz/blog-engl/index.php?action=item&itemid=5, I realize that I am a rank amateur when it comes to flatness......

    Tim
     
  7. dancqu

    dancqu Member

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    Have you mistaken distorted surfaces for curvature of field? Dan
     
  8. jeroldharter

    jeroldharter Member

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    Thanks for the input.

    I use a Beseler alignment tool, the one that has two bubble levels at right angles. The lens board, negative stage and baseboard are all in alignment. Then I place the easel on the baseboard. The center of the easel is closer to the lens than the 4 corners so it is crowned slightly. I would not have noticed this by looking. Likewise the effect is modest at smaller enlargement ratios. However, on a 16x20 print (4x5 negative) the 4 corners are unsharp. The top corners of the easel are worse than the others.

    That is interesting that the vacuum easel might even out when the vacuum is activated. But I really don't want to use it (even though I bought it). Why would someone prefer a vacuum easel for baseboard enlarging anyway?

    I don't think it is lens field curvature because I can measure it on the easel with the levels. The lens is a Schneider Apo-Componon 150 mm. I think I have had this issue all along but to a minor degree. Must be something in the are this time of year.

    For the reasons mentioned, stopping the lens down does not help much.
     
  9. ic-racer

    ic-racer Member

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    OK, so you are in a 'low magnification' range (4x to be exact), so paper/easel/baseboard problems could possibly be evident. We can still use that equation to find the smallest aperture to bring everything in focus (just like focusing a view camera). The 'dv' (which I neglected to mention is in millimeters) would be the amount of 'crowning' evident in your easel (assuming, as you said, your negative is perfectly flat and everything is in appropriate alignment).

    So, if you have about 4mm of crowning the equation would work out like this:
    dv = 4mm
    M = 4 (16x20 print from 4x5 negative)

    So the minimum aperture needed (taking into account both diffraction bullseyes and out of focus circles of confusion) would be:
    N_max = (20/5) * sqrt(4)
    N_max = 4 * 2
    N_max = f8

    Likewise, if you can't get it all in focus at say f22, your easel must be crowned up 30 millimeters from the corners.

    Can you confirm that when the easel is removed everything is correctly focused on the baseboard? Something other than your easel seems amiss (based on the info at hand).
     
  10. jeroldharter

    jeroldharter Member

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    ic-racer,

    Thank you very much. I will try to confirm on the baseboard tonight and will try stopping down to f22 to check out when I print the next 16x20. I went back to 11x14 this afternoon with a typical working aperture for f11 1/2.

    Jamie
     
  11. dancqu

    dancqu Member

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    If the field is convex downward I'd expect easel center
    to first come into focus then the corners with a mite
    less extension of the bellows. Has that lens any
    specific best magnification?

    A long shot: By way of trouble shooting you might try
    a red, green, and blue focusing. Dan
     
  12. jeroldharter

    jeroldharter Member

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    I did confirm that the focusing is even throughout from center to all four corners on the baseboard. The easels are the problem.
     
  13. RJS

    RJS Member

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    How much 'bowing' do you have? Lately I have been fooling with glass negative carriers, particularly for 35mm and closely inspecting prints I have made over the years with glassless carriers (Beseler 45MX), and I am unable to detect unsharpness in the print made with the glassless carriers. I can see that the negatives are not held flat, and I know glass will keep them flat. But given I haven't been able to detect a difference in the prints I wonder if the glass carrier is worth the bother for 35, at least. For 4X5 I have negaflat, and 2 1/4 the Beseler Negatrans with glass does quite a good job. But this problem is the same as yours; how accurate do you really need to be? If you you can't see a difference in the print, why worry?
     
  14. ic-racer

    ic-racer Member

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    Good.
    I once had an easel that I beat on with a wooden mallet to flatten it out. The steel was pretty solid so it was not easy.

    Getting back to the issue of depth of field. I presume that since you shoot 4x5 that you are familiar with focusing the view camera using the method of Paul Hansma (http://www.largeformatphotography.info/fstop.html) ? Then you should be able to do the same with the enlarger.

    So, focus on the peak of the easel hump. Note the distance marker on your enlarger column. Then (without touching the focus knob) move the enlarger head downward to focus on a corner. Make note of the distance between the two points in millimeters. Then position the head at the middle point between the two positions. You can use the formula to find your f-stop or I have a hunch you can just use f22.

    If the print is still not acceptable, then either there is a communication gap or the laws of physics have been defied :D
     
  15. jeroldharter

    jeroldharter Member

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    Thanks. I agree. I will try that with a 16x20. Appreciate the advice.

    I feel like using a mallet but I find it hard to do.
     
  16. John W

    John W Member

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    If it makes you feel any better about using a mallet, I'm in the position of just having received what was a few days ago a gorgeous near-mint Saunders VT2000 easel. It was improperly packed (by UPS) and manhandled in shipping (by UPS)... the outer steel shell of the easel, especially at the corners, took a beating. The front left corner is so badly impacted that it buckled the steel along the bottom front edge. I feel ill just thinking about it. Fortunately, the top frame, blades, and bed are fine (protected by the outer shell!)

    I'm going to make a claim against UPS for repairs. Far beyond the mallet: It's going to be rather odd going to bodywork shops for an estimate on fixing my easel!
     
  17. dancqu

    dancqu Member

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    Support all four corners then stress flatten by weighting
    the center. Might work. Dan
     
  18. ic-racer

    ic-racer Member

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    When I was dealing with a little hump in my Beseler 16x20 easel, I used a wood mallet and also a steel hammer with a block of wood. I also stood and jumped on it. I couldn't really make any change in it.

    This may not be relevant here, but it is something to think about if you still are having trouble. My little off-center hump in the easel was causing a buckle in the paper. No problem in itself, but I eventually traced a 'blurryness' problem to the fact that the buckle in the paper was shifting and settling out after I closed the easel. Thus causing a problem when closing the easel and hitting the expose button in rapid sequence.
     
  19. dancqu

    dancqu Member

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    I've not read all posts dealing with easels but have
    read a lot of them. This is the first time humps in
    easels has been the issue. No wonder vacuum
    and sticky back easels have some use.

    Clinging bubbles and eddy currents with running
    water slot washers are two more problems supplied
    by the manufacturers of darkroom equipment.
    No wonder a few use still water soaks. Dan
     
  20. Ronald Moravec

    Ronald Moravec Member

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    Not all enlarging lenses have flat fields. Leicas are the biggest culprits. It is a trade off to keep astimatism under control and they do it with all their lenses.

    The other probably bigger culprit is not having a dead flat negative. Even with a perfect lens, only the center or the corners will be in focus. I have had some sucess matching curved field lenses with non flat negatives. The defects seem to cancel.

    Best results are with a true flat field lens and double glass neg carrier.


    There is no way a 1/8" bow in the center of an easel can put the image out of focus and there is no way you can have a bow that big.

    The double bubble level is ok to get the lens stage to match the base. It is not accurate enough for the lens. You need a lazer device or one of the other products for this. I just use my Peak 10x grain mag at 16x20 and match left/right sides, then forward/backward. After you do this, put it in the corners and all four will be sharp at one time. Then work on the center with a proper lens and glass carrier.

    BTW, every lens is different. So you can`t unscrew one and put another one in it`s place. I know it`s more than you wanted to hear.
     
  21. dancqu

    dancqu Member

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    Also enlarging lenses have a best enlarging diameter.
    Departure from optimum may exacerbate the problem.
    I note the OP mentioning moving to greater diameter
    enlargements. Dan
     
  22. Ronald Moravec

    Ronald Moravec Member

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    If there is a hump, the metal is stretched. Beating it down can at best make it pop the other way.
     
  23. jeroldharter

    jeroldharter Member

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    Many people have chimed in on this thread. I appreciate all of the input. Some have sent me detailed PM's which are very thoughtful and appreciated. Sorry I have not responded to them individually.

    At this point I am not having any problems. I think I was having a combination of issues. The easels are slightly bowed, but very slightly and not enough to make a difference normally . Also, I think the the 4x5 negative in the carrier was not popped but bowed. I use a Negaflat carrier which is excellent for flatness but I had the negative sitting in the carrier at least overnight without re-setting it so I think it sagged a little. Also, I had aligned my lens with the Beseler tool but then I ponied up and bought the Verslab which is much more precise. I still don't have it perfectly aligned but very close. And I stopped my lens down a little for good measure as well as for base exposure times in the 20-30 second range which I like.

    So the combination of adjusting the negative in the negaflat, aligning the negative and lens with the Versalab, and using f11-16 on the lens has done the trick, at least up to 16x20 prints which is as large as I plan to go (except for the occasional 20x24 of course).

    So thanks again for all of the ideas and thoughtfulness of replies.