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  1. #11

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    The way the OP describes his problem it sounds as if the heat warping actually brings the neg into focus - admittedly the exact opposite of what you'd expect.
    It can happen that way if the negative is first allowed to heat sufficiently to “pop” it, the central area of the negative is focused in the popped condition, and then the lamp is switched off.

    The negative is thin and cools quickly allowing it flatten back into the original plane while the paper is positioned on the easel.

    Then the moment the lamp is switched on the image is fuzzy because the central part of the negative has cooled and dropped below the plane of focus. But when the timer is tripped, the negative heats and the central area slowly bellies back upward to where it was focused when hot, the image goes from fuzzy to sharp—at least in the central area—during the heating period until the negative is once again fullypopped. But during the transition the sharpness of the projection varies. The result is an unsatisfying print that lacks the full sharpness the negative and lens can deliver.

    The cure is to install heat absorbing glass. This costs about 0.3 stops per sheet. The HA glass supplied with US enlargers is 1/8” in thickness.

    I found that the flatness of my heated negatives was greatly improved in my Beseler 23C II condenser enlarger by installing a single sheet of HA glass, but dense negatives requiring long exposures still got slightly fuzzy over long exposures of, say, 30 seconds or longer. This enlarger is equipped with a 75-watt opal enlarger bulb (horizontal burn PH-111 or vertical burn PH-140, depending on when it was made).

    I removed the sheet aluminum filter drawer from the lower filter slot so that I could install a SECOND sheet of HA glass. With 2 sheets of HA glass the negatives apparently don’t move at all even during exposures of up to 60 seconds or more. The 2 sheets of HA cost me 0.6 stops, but that’s a small price to pay for negatives that stay flat and well focused throughout the exposure.

    Since I’ve used up both filter slots with HA glass I’m forced to use the Ilford below-the-lens Multigrade filters. They work great and don’t degrade the image a bit.

    Some folks use expensive glass carriers, but the excess heat really should be eliminated first before going to a glass carrier. It might be that exceptionally long exposures, such as making a horizontal projection on mural paper (I think Ilford supplies this up to 56” wide) might require a glass carrier in addition to HA glass.

  2. #12

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    Quote Originally Posted by pentaxuser View Post
    IanC The way the OP describes his problem it sounds as if the heat warping actually brings the neg into focus - admittedly the exact opposite of what you'd expect.
    Actually, that's what you would expect.

    While you are focusing, the heat warps the negative. By time you chase the changing focal plane and get it into focus, the negative has reached equilibrium. Then you turn off the lamp and go to get the paper. The negative now has time to cool and warp back down into the cold equilibrium position.

    By time you get the paper, put it in the easel, position it, close the easel and reach for the timer, the negative is out of focus. Then when the timer comes on, the heat starts warping the negative back into the position it was finally focused at. It might never have time to get there and even if it does, the percentage of time spent at that state may be a small part of the timer exposure.

    These are the symptoms the OP describes.

  3. #13

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    sounds like the head might be slipping down the column too ...
    silver magnets, trickle tanks sold
    artwork often times sold for charity
    PM me for details

  4. #14
    Ian Grant's Avatar
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    Quote Originally Posted by jnanian View Post
    sounds like the head might be slipping down the column too ...
    Usually they move up the column because the couter weight spring has to be stronger than the gravvitational effects of the mass of the head.

    Ian

  5. #15
    Bob Carnie's Avatar
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    On my Omegas I have seen the bellows drop if not well maintained.
    This requires some tightening , this usually happens with 35mm position on my systems.
    Once a year I have a tech look at this issue on the Omegas, the durst and deveere never have this slippage.



    Quote Originally Posted by Ian Grant View Post
    Usually they move up the column because the couter weight spring has to be stronger than the gravvitational effects of the mass of the head.

    Ian

  6. #16

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    Whenever I need to use a 50mm lens for 35mm work, I also use a recessed board for either the Omega
    or the Durst enlargers. Generally I prefer a longer lens, but there is the risk on the Omega of the bellows
    slipping if overcompressed. The idea of not using a glass carrier in an enlarger seems utterly barbaric;
    holding precise focus would seem impossible.

  7. #17

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    Thanks guys...

    I was also thinking it could be heat warping the negative, but the problem is that it hasn't done this before and then suddenly after 40 perfect prints with my new enlarger, they all start doing this? I have a glass carrier I will try and customize to fit the beseler.

    I can literally watch the negative come into focus, which supports the heat/warping theory, but could it be something else? A power supply maybe? I know intensity of light doesn't effect the focus, it's the negative plane. But any other theories before I dive back down there?

  8. #18
    Bob Carnie's Avatar
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    Can't agree more strongly.
    Quote Originally Posted by DREW WILEY View Post
    Whenever I need to use a 50mm lens for 35mm work, I also use a recessed board for either the Omega
    or the Durst enlargers. Generally I prefer a longer lens, but there is the risk on the Omega of the bellows
    slipping if overcompressed. The idea of not using a glass carrier in an enlarger seems utterly barbaric;
    holding precise focus would seem impossible.

  9. #19

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    On my Omegas I have seen the bellows drop if not well maintained.
    I have a D5 that does exactly that, the head does not move but the bellows lock is a bit loose and I have seen it creep down and watched the focus change.

  10. #20

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    Quote Originally Posted by DREW WILEY View Post
    The idea of not using a glass carrier in an enlarger seems utterly barbaric; holding precise focus would seem impossible.
    The idea of using a glass carrier seems barbaric. I've enlarged glassful and glassless and I prefer the latter for cleaner results. Less spotting.

    However, that is for 35mm negatives. I haven't enlarged 8x10, but it seems that people like Clyde Butcher use glass for 8x10 negatives.
    Last edited by Monito; 08-10-2011 at 06:19 PM. Click to view previous post history. Reason: 8x10

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