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Thread: What is anti-Newton ring glass exactly

  1. #31

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    Re: What is anti-Newton ring glass exactly

    Drew, the format reducing mask can be placed over the top glass, with no harmful effect.

    The 138 I use came with a 24x36mm cartoon black mask placed over the top glass...

  2. #32
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    Yes, Pere, but unless you have registration pins and attached registration loops involved (doable), it means taping the mask on, then needing to remove tape residue afterwards. In such cases, "removable" tapes are preferable, though due to the heat of enlargement, especially using halogen colorheads, even removable tape gets a certain amount of sticky stuff transferred to the carrier or its top glass. I keep PEC cleaner handy.

  3. #33

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    Re: What is anti-Newton ring glass exactly

    No taping, the mask had the same size than the glass and it was retained with the same clips than the glass

  4. #34
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    Well, unless the mask is made from something rigid like black anodized aluminum, it might have a tendency to warp under heat and need to be firmly clipped or taped too, and not just registered in position - again, an issue affecting colorheads more than cold light sources.

  5. #35

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Drew Wiley View Post
    Well, unless the mask is made from something rigid like black anodized aluminum, it might have a tendency to warp under heat and need to be firmly clipped or taped too, and not just registered in position - again, an issue affecting colorheads more than cold light sources.
    Also condenser type enlargers are much more efficient and they use only a fraction of the power than a diffusion head. The 138 with a LED lamp has a low reheating in the film. With the tungsten lamp what reheats is the 138 lamp box inside, that is painted in black.

    Film reheating in the film from a tungsten lamp diffuser can be addressed in the design by placing a hot mirror to block IR or reflecting only visible with a cold mirror. If the (over the condensers) 138 mirror is replaced by a cold mirror then most IR won't be reflected down. The 138 I use came with a hot mirror to block IR in the filter drawer.

    Film reheating happens more with BW film as silver is opaque in the IR, color film is transparent in the IR, so most IR is spread on the photopaper, while dense BW silver areas take the IR.

  6. #36
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    You seem to be talking about some awfully old 138's, Pere. All of mine have used mirror boxes and diffusion. I do have an old condenser head stored away somewhere - never used it, and sold off all the condensers long ago.

  7. #37

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Drew Wiley View Post
    All of mine have used mirror boxes and diffusion. I do have an old condenser head stored away somewhere - never used it, and sold off all the condensers long ago.

    the 138... it is condenser, it is diffuser and it is everything in between. You may use this: a "LAPAL ground-glass diffusing screen can be inserted into the filter-holder", or other frosting intensity to adjust the degree of diffusion you want to nail a perfect illumination for the job, or a diffused illuminator in the condenser drawer. You may also use a color head solution or 8x10" adapter, to have a 8x10" capability in a moderately sized machine.

    also, thanks to LED retrofit it is VC, and it can expose 2m prints in 40s at f/11 thanks to efficient illumination. Bulb moves x-y-z so you compensate fall-off even if it's not centered in the taking.
    Last edited by Pere Casals; 14-Nov-2019 at 03:52.

  8. #38
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    Thank you, Pere. I was already aware of all that, and of the various ways these old condenser heads have been modified, even into halogen color enlargers. But there are obviously good reasons why they offered more modern colorhead designs for the 138 chassis using mirror boxes. Evenness of illumination is one of them. You don't have to fiddle with switching specific condensers. Analogously, they did offer a rather weak cold light which slipped right into the condenser position in the head, but an oversized cold light not constrained by that small dimension works far better. In other words, in my own 138 modifications, I was not after "everything in between", but things "wholly beyond" the inherent limitations of the condenser head housing. In the case of my first 138, I was punching large heavily-masked Ciba prints requiring far far more illumination than what you describe. Thankfully, current RA4 options print much faster.

  9. #39

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    Re: What is anti-Newton ring glass exactly

    Quote Originally Posted by Drew Wiley View Post
    current RA4 options print much faster.
    I've calculated, with the lux meter, that with the 138 with condensers a 150W LED a 2m print can be exposed in under 40S at f/11, avoiding paper LIRF and needing less a G type lens that's required if wanting performance at large apertures, f/11 also allows greater DOF to cast all "through the negative"quality on the print.

    I find that the 138 with condensers delivers an even illumination, and that the with xyz movements of the bulb lens and negative fall-off can be addressed, of course Callier effect only happens with BW film, but condenser efficience allows to make monster prints with 1/10 of the heat in the negative than with diffusers.

    My bet is semi-diffused, condensers with and adjustable amount of diffusion.

    Next step will be checking if an special LED retrofit will work OK with color paper. I plan to project an IT8 transparent target (came with an EPSON) on RA-4 to see if I can obtain the same with LEDs than with Tungsten, scanning both prints (from the IT8) alongside and comparing.

  10. #40
    Drew Wiley
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    Re: What is anti-Newton ring glass exactly

    Why not do it on real RA4 paper instead using an actual color negative control? That would be a lot more efficient and realistic.

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