Cold head? What do you eat it with?

Discussion in 'Darkroom Equipment' started by Andrey, Jan 29, 2008.

  1. Andrey

    Andrey Member

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    I've been reading about enlargers and have questions.

    There's a condenser and a diffuser.

    With a condenser there's a set of lenses which focus light on the negative.

    With a diffuser, there's a matte screen that's illuminated behind the negative.

    Roughly, these two setups make the same pictures. There's also a "point source" enlarger which gives higher contrast and different look, right?

    1) What does the choice of head have to do with it all?
    2) What are the advantages of a cold head?
    3) Are the MC filters calibrated to a specific color temperature?
    4) A bit irrelevant - is there anything speical about a Zone IV enlarger?

    Thanks

    Andrey
     
  2. Paul Howell

    Paul Howell Member

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    Diffusion enlargers seem to show less dust and other negative defects, point source really shows off dust and does print with much more contrast. Most condenser enlargers use a frosted blub which is sort of semi diffuse. Cold light uses a cold gas tube. I have all three, a Durst 601 with a color head which is a diffusion head, an old converted Russian enlarger which I use for point source for 35mm and a D III with a condenser and cold light heads. I like the cold head for 9X12 and 4X5, condenser for 6X6 and 35mm. If I could only have one enlarger it would a diffusion enlarger with a color head.

    I have never used a Zone VI, no longer made.
     
  3. jeroldharter

    jeroldharter Member

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    1) Cold light or dichroic diffusion light sources are more forgiving for dust and less contrasty. I prefer dichroic light sources.
    2) Cold lights are less expensive for basic units. they use diffused lights. The bulbs last a long time. However, the light output varies with temperature so adding special timers to measure the change in output adds to the cost.
    3) MC filters are calibrated to give specific contrast values for specific papers. Either Kodak or Ilford work fine.
    4) Zone VI is somewhat unique in that it is a 5x7 format. Also, Calumet sells a 4x5 LED light source that is interesting and only works on the Zone VI.
     
  4. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    1) In practice, it was found that there is only a very subtle difference between the image produced by a condenser and a diffusion head. Cf. Ctein's article to this effect in his book "Post Exposure." The gist of it is that a condenser will give you a little bit nicer highlight contrast, and a diffuser will give you a little bit nicer shadow detail. That's that. Well, and the dust thing as well. Dust is a bit more visible with a condenser enlarger. So the different light sources are just different possibilities for the advanced printer.

    2) A cold head is nothing else than a diffusion source. It's not a different category of light source, it's just a high-quality neon and a sheet of frosted glass. Most diffuser enlargers usually use tungsten or halogen bulbs, which tend to emit a lot of infrared and heat. In comparison, the cold light produces way less heat. But you might as well get LED for the very best in heat, light stability, economy, longevity, etc.

    3) MC filters are calibrated for 3,200K tungsten light, of the kind you would usually find in a condenser or a diffusion enlarger. Some Zone VI cold lights were built with graded papers only in mind. Their light is bluish, and you need to use about 40CC of yellow to correct the light temperature if you print with Multigrade.

    4) Never bought one, but they sure looked sturdy and nice.
     
  5. Deckled Edge

    Deckled Edge Member

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  6. Andrey

    Andrey Member

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    Thanks for the replies.

    What is the problem with the IR emission? Is a paper sensitive to the IR?

    It seems that a cold head with a compensating timer is a very complicated solution. No?

    If I can live with the heat, is there a major reason to get a cold head in terms of image quality?
     
  7. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    It depends. Some cold lights are balanced for graded papers, and thus have a bluish light, whereas others are balanced for the tungsten temperature of VC filters. If your light looks blue, then you need the CC40Y, if it looks more white/yellow, then you should be fine.
     
  8. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    Paper is not sensitive to IR, but your negative is sensitive to the heat generated by the light source.

    A compensating timer is a gadget, useful but not essential.