Enlarger precision

Discussion in 'Darkroom Equipment' started by hoffy, Jun 5, 2011.

  1. hoffy

    hoffy Member

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    Last weekend I discovered that my enlarger wasn't as square to the baseboard as I hoped. Today I decided I would try and rectify this.

    I have discovered that I needed to shim the column by around 3mm on the front of the column to get that square to the baseboard. I also checked the alignment between the bottom of the housing (just below the negative holder) and the lens board and have found that there is a bit of difference, around half a mm from front to back (side to side is adjustable, so I have got that reasonably spot on). I can see it is due to the slop between the rails and the lens board housing. I have to admit, this annoys me a little.

    Am I being pedantic? Should I really be chasing better precision or am I wasting time?

    Cheers

    Cheers
     
  2. Steve Smith

    Steve Smith Subscriber

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    Nothing wrong with wanting it as correct as you can get it. With an enlarger, the most important parts to have correctly parallel are the negative holder and the lens mount. You can get away with a fair amount of error at the base board but a tiny error in the negative position will translate to a lot of focusing error.


    Steve.
     
  3. ic-racer

    ic-racer Member

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    The degree of precision to which you align the negative and lens is dependent on your magnification. The greater the magnification, the more closely you need to have the lens and negative aligned.

    If you work backward through the 'diffraction/defocus' equation for enlarging you can calculate how far off you can be and still have a good print at a reasonable viewing distance.

    If we say 10x enlargement of 35mm negative at f8 and a 50mm lens:

    Focal spread at the baseboard level will be 20mm at f8 based on the diffraction/defocus equation ( f8 = 20/(10+1) * square root of 20)
    With this number and the simple lens equation (1/f = 1/p + 1/q) we can calculate the side to side displacement of a negative where each side focuses 10mm higher or lower on the baseboard from the center of the negative.

    1/50 = 1/600 + 1/54
    1/50 = 1/800 + 1/53

    So one side of the negative will be 54mm from the lens and the other side of the negative will be 53mm from the lens. So the approximate the maximum allowable negative stage displacement for an 10x enlargement of 35mm frame is about 1mm.
     
  4. Jim Jones

    Jim Jones Subscriber

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    It is too common for the weight of the enlarging head to gradually tilt the column forward, requiring shimming as Hoffy did. This is especially true of enlargers with fiberboard bases. Replacing these base with heavy plywood (with the surface plys running from back to front) may be worth while.
     
  5. hoffy

    hoffy Member

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    Thanks for the replies. By the sounds of things, I am borderline pedantic at the moment, but I would like to get the alignment between the lens and the negative holder spot on. If you are saying 1mm maximum at 58mm, I would probably be OK. I know my prints are good enough, but I have hardly done decent corner to corner checks.

    One thing I would like to do is possibly build a steel frame, for which I could mount the enlarger to. I am not 100% sure whether I will go ahead with this, but it certainly will help to enable a good base point to start with.

    Cheers
     
  6. tkamiya

    tkamiya Member

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    Speaking from experience....

    Aligning an enlarger precisely is pain in a butt and without correct instruments, it's pretty much impossible. After struggling with various methods and many makeshift tools, I ended up sourcing a ready-made tool for the job to finish it up. Carpenter's level isn't even close to sensitive enough.

    You hear lots of stories like if your image is perfectly square on the baseboard, it's good to go. NOT SO! It is possible to have a square image and have one corner perfectly in focus but the opposing corner perfectly OFF focus. Try to bring that in focus and the image now isn't square.... Then do the other corner and the opposing corner. It's quite maddening! Oh, let's not forget baseboard warping, vertical support sagging, and side to side play.... Raise the head and lower, it's off again.

    Unless you have the correct tool and have the wills to spend hours on end to get it right, if it's close enough, I wouldn't mess with it. I was forced to do one because I had to rebuild my second enlarger. It taught me a lesson NOT to try to better my primary enlarger.
     
  7. Ralph Javins

    Ralph Javins Member

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    Good morning;

    Your reference to "the correct tool" is intriguing. What tool do you suggest?

    Will something like the LASER Alignment Tool from Freestyle meet your requirements?
     
  8. tkamiya

    tkamiya Member

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    I used a Bessler's alignment tool that I could borrow. (my enlargers are Omega) This device has two bubble levels mounted at a right angle to each other. Very nice... Laser kind would be nice but I really didn't want to buy one.
     
  9. ic-racer

    ic-racer Member

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    The critical alignment for big enlargements is between lens and negative. The exact analogy is taking a picture of a billboard at infinity. It doesn't matter if the billboard is perpendicular to the film plane.
     
  10. Jonathan R

    Jonathan R Member

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    I like simple solutions. To check alignment, I use a piece of black (developed) film with a grid of lines scratched on the emulsion side with the point of a sharp knife. At full aperture and at the enlarger height required, I slip narrow card shims under one side of the negative carrier until I have it spot on. For a 12" x 16" I need 3 thicknesses of postcard. I then expose the paper with the lens stopped down to f5.6 or f8. It is worth the effort.

    In this way I also discovered that my enlarger column (I would guess most enlarger columns) droops when the enlarger is up towards the top. My solution was to do away with the baseboard, fixing the enlarger column directly to the bench, and bracing it against the wall behind using a length of threaded bar and some nuts inside the column. These measures must also help to prevent that other source of unsharpness, vibration.
     
    Last edited by a moderator: Jun 7, 2011
  11. hoffy

    hoffy Member

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    Excellent advice there Jonathan. I will possibly look into that.

    Cheers
     
  12. Jim Jones

    Jim Jones Subscriber

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    Jonathan's advice works for me, too. One can also use a sheet of clear film with one surface lightly sanded with both coarse and fine sandpaper in the negative carrier. The coarse lines provide quick rough focusing, and the fine lines permit precision fine tuning. I'd use tape, perhaps duct tape, instead of cardstock for lensboard shims. It stays in place.

    The object of enlarger alignment is not to get film carrier, lens board, and easel parallel: it is to get the image sharp on all four corners. Perfect parallism does not insure this; for example, the lens might be poorly assembled or mounted. Jonathon's solution focuses (poor pun intended) on solving the real problem.
     
  13. Monito

    Monito Member

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    Does this shimming work for only one height? Or can you shim and have the focus maintain at all heights? Is that perhaps true only in principle, assuming a well aligned column/support?

    I will be tuning an old Beseler 23C II that I was given, so I'm looking for guidance. First step is I will be gluing the lens bellows to the stage since it has totally detached.
     
  14. semi-ambivalent

    semi-ambivalent Subscriber

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    Brace that column

    Monito,

    I have a 23CII XL and had a great deal of trouble with vibration. I used a couple pieces of pipe strap screwed into the concrete wall behind the enlarger on one end and screwed into some holes on the top of the girder assembly at the other. I may have drilled the enlarger holes myself. Man, did that ever help. At the girder end I made the holes in the pipe strap "too big" and pinched it using washers. That way if my holes were off I wasn't twisting the girder assembly. Only then could I successfully align the lens/negative carrier. A big housing at the end of the girder "stick" is just begging for problems.

    HTH,

    sa
     
  15. Monito

    Monito Member

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    Thanks semi.

    I wish I could find a way to brace the column, but I need to be able to slide the enlarger back from its deployed position to a stowage position to allow access when the room is not used as a darkroom.
     
  16. ic-racer

    ic-racer Member

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    The 23CII should have an adjustable lens stage, so no need for any negative stage shims. That is just for those enlargers that are not adjustable.
     
  17. Ronald Moravec

    Ronald Moravec Member

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    A cheap carpenters level is quite good enough so long as it is repeatable error. Always point the same end to the right or back depending on what you are lining up.

    I use a 10X Peak grain magnifier to check grain midway on all four sides to set the lens to negative. Raise the magnifier to see if the side you are checking is too low or too high.

    Now you will find every neg carrier is different, even supposedly flat ones like Omega D. Then you find every lens is off also. Use the same mount and you find the lens axis is never perpendicular to the mount/threads. So set it all up with most common neg size/lens. then use tape shims on the other carriers. Buy a mount for each lens and custom adjust each.

    I got mine perfect with all lenses.

    The three Leica enlargers, one V35 and two 1C are all perfect right from the box. And they stay that way. The Omegas are pathetic in comparison, but can be worked to perfection as I described.
     
  18. hoffy

    hoffy Member

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    Well, I tried that out tonight. Worked a charm!