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Thread: aristo cold light head

  1. #1

    aristo cold light head

    Hello- I have an Aristo VCL4500 cold light head on a Besseler. I tend to work around technical problems, but have recently become tired of consistently burning in the left half of prints made with this set-up. Is the lamp bad, not positioned properly, or is something else wrong?

    Thanks- Jon

  2. #2
    おせわに なります! Andrew O'Neill's Avatar
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    aristo cold light head

    I have the same head. It needs to be as close to the negative as possible. Mine sits right on top with no gap. Is the head centred over the negative? That is one weakness of this head. It just barely covers 4x5. See if you can place the head as close as possible to the negative.

  3. #3
    Abuser of God's Sunlight
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    aristo cold light head

    none of these cold lights illuminates evenly. you can improve things by making a mask with some lith film. just project the image of your cold light (no neg carrier) onto a big piece of lith film, at 1:1 magnification, and develop in a strong developer, like whatever you use for prints. if you have some sheets to play with, you can adjust exposure and development until the litghtest parts of the mask are clear, and the darkest parts are dark enough to cancel out the bright spots on the light source.

    you just cut out the mask and set it on top of the frosted plexi of the cold light (making sure to align it properly).

    i borrowed one of those print exposure meters from a friend to help do this accurately. i got the whole thing even within about a third of a stop. not enough to eliminate the problems, but it helped a bunch.

  4. #4

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    aristo cold light head

    That’s and interesting idea, paulr. I was thinking about doing something similar with my single tube. The VCL4500 is a 2-tube design, and adjusts contrast by dimming the blue tube. Would you make 2 lith masks—one at each contrast extreme—and average the results?

  5. #5

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    aristo cold light head

    "none of these cold lights illuminates evenly."

    The VCL 4500 that I used for about 12 years illuminated very evenly with prints up to 11x14. There's a very simple test to check for even illumination. Put a smooth piece of mat board, paper, whatever, on top of your easel, raise the head to whatever point you want with a negative carrier but no negative in place. Then measure the corners and center of the board, paper, etc. with your spot meter. This should tell you whether there's a problem with your head.

    FWIW, I have some difficulty with the idea that your head is causing the left half of your prints to be consistently underexposed. Given the construction of the VCL4500 with its two sets of intertwining tubes (as I remember the construction, I sold the head after I began printing digitally so I can't check my memory of what the tubes look like), if one burnt out it wouldn't just be the left side of the print that would be affected, you wouldn't be able to make a decent print at all. And if one of the tubes somehow dimmed more than the other but didn't burn out entirely the contrast of the entire print seemingly would be be affected, not just one half of it.

    It's pretty hard to mess up the positioning of the head and negative stage with a Beseler M series enlarger. The head will only fit in one position and the negative holder will only go in one place. You do have the upper bellows fully compressed, right?

    I'm sorry I can't suggest a source of the problem but it seems highly unusual for one half of your prints to be consistently underexposed while the other half is fine. Have you checked the translucent plastic sheet on the bottom of the head? Conceivably half of it has gotten dirty or something else has happened to it that's causing the light passing through half of it do be dimmer than the other half. That, or some sort of obstruction in the light path from negative to paper, is all that occurs to me and neither seems real probable.
    Brian Ellis
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    a mile away and you'll have their shoes.

  6. #6
    Eric Woodbury
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    aristo cold light head

    Imagine what your lens 'sees' if you take the diffuser out. Since the diffuser is not perfect and the lens doesn't go completely, absolutely out-of-focus just past the neg, the lens will see through the diffusor into the lamp chamber. Using a longer lens, the longest you can for a given enlargement ratio, will lessen the angle of projection and reduce how much of the lamp housing sidewalls you might be 'seeing'.

    If you want to see how uneven your illumination is, remove the negative and make a print of just the light. It won't be even. Very hard to make them even. A bigger light source helps. As noted, keeping the diffusor as close to the neg as possible is important and a mask can trim things, but it costs you some exposure time. The VCL4500 is not that bright.
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  7. #7
    Abuser of God's Sunlight
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    aristo cold light head

    "Would you make 2 lith masks—one at each contrast extreme—and average the results?"

    yikes, that sounds a little complicated. i think the first thing i'd try is to just make one mask at my most common setting, and see how well it does. it might be enough of an improvement on its own that you don't have to get fancier than that.

    " ... The VCL 4500 that I used for about 12 years illuminated very evenly "

    i should have been specific and said the round ones like the aristo and the zone vi aren't even. i have no experience with the big rectangular ones like the 4500. based on looking at them i'd guess they do better, since the tubes seem to extend past the round opening . in the round cold light heads, everything's crammed into a cylinder that 's the exact diameter of the neg diagonal. so in addition to the image of the tube itself, you you deal with a fair amount of falloff in the corners.

    "As noted, keeping the diffusor as close to the neg as possible is important ..."

    i came up with a hair-brained theory a long time ago that you'd improve evenness by getting the unit farther away from the neg. i actually built a little chamber, with frosted plexi above and below, with a shelf in the middle for inserting split contrast filters. the idea was to make inserting filters above the neg easy with the zone vi head, and to improve evenness by by having 2 diifusors with space between them, instead of just one.

    i might have gotten an A in 6th grade shop class for all my efforts, but the resutls were a disaster! as you probably would have guessed. light falloff at the edges was so extreme i never even got one useable print out of the thing.

  8. #8

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    aristo cold light head

    "Since the diffuser is not perfect and the lens doesn't go completely, absolutely out-of-focus just past the neg, the lens will see through the diffusor into the lamp chamber"

    Perhaps I'm missing something but I don't understand that statement. With the VCL4500 the diffuser is above the lens so the lens doesn't see through the diffuser. The light passes from the diffuser through the negative to the lens and then to the paper.

    "I should have been specific and said the round ones like the aristo and the zone vi aren't even. i have no experience with the big rectangular ones like the 4500."

    The 4500 is an Aristo and it's round, not rectangular. I can't speak for any except the one I used for 12 years but that one was quite even from center to edges and corners, at least with prints up to 11x14. I used to check it occasionally using the test I described above. But regardless of whether I just got lucky or not, as I understand Andrew's description of the problem it isn't that he's got light fall-off from center to edges, it's that the entire left half of his prints is consistently underexposed. Uneven illumination with an enlarger usually manifests itself as a difference between illumination at the center of the print and illumination at the edges. That doesn't sound like what he's experiencing.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  9. #9

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    aristo cold light head

    At the risk of pointing out the obvious, you might consider contacting Aristo for technical assistance. If their tech support is up to the level of service offered by Louise on the sales side, you should be home free.

    They are on the Web at aristogrid.com; considering the range of products they offer and the length of time that they have been in the business, I'd be surprised if your difficulty hasn't come up before.

    Good luck.

  10. #10

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    aristo cold light head

    During a workshop years ago John Sexton advised us that the standard diffuser for these coldlights is too thin. A thicker one was available at that time from Meyrick Photo in Carmel or Monterey for about USD 10.00. That would smoothen out the uneven lightintensity from the grid. He also recommended darkening the inside of the lamphousing centrally somewhat with lightgrey paint if I remember correctly, to diminish the central hot spot.

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