Zone vi cold head

Discussion in 'Darkroom Equipment' started by Doug Darling, Jul 6, 2013.

  1. Doug Darling

    Doug Darling Member

    Sep 27, 2011
    Northern Col
    Medium Format
    Sorry if this has been asked before.

    I picked up a Omega D2 enlarger, with a zone vi cold head. Two cords one for the light one for the warmer. One bulb, and it has a connection for the variable controls. Here are my questions.

    1. Do I need the variable controls, which I don't have.
    2. I could find no makings on the light even though I pulled it apart, cam I assume which bulb I have, and can I use VC paper with below lens filters.
    3 I alco have the parts to make it back to the condenser version, and preferences and why.

    It has taken 30 years for me to have a wet darkroom again. Your help is appreciated.

    Doug Darling
  2. NedL

    NedL Subscriber

    Aug 23, 2012
    Sonoma County, California
    Multi Format
    There are others here who can probably answer better than I, but I'll chip in with what I'm doing. It might or might not be the best advice. I have a zone vi cold light and do not have a variable timer or variable control. Mine has the original light which does not have much green in it. If yours has a V54 bulb it will look turquoise or almost aquamarine color. Mine looks white. The v54 bulb, if I understand correctly, will work with standard VC filters.

    There were several variations of the cold light head. Mine has a separate power supply unit. I'm assuming you have that? It contains the high voltage transformer. I can't tell from your post if you've turned your cold light on or not.

    The cold light has a photodiode in it to monitor the brightness. That's the socket that would attach to the variable timer. I took mine apart and monitored the diode resistance very carefully ( with a small series resistor so as not to run too much current through it... depends what kind of ohm meter you have. ) What I found is this:

    The brightness increases for the first 20 to 30 seconds, then levels off at a very stable level for several minutes, finally falling off very slowly after that. As the tube warms up, from use and from the heater, this "warm up" time becomes less and less. What I do is before each exposure, I hold a card under it for 30 seconds. This way all my exposures start at the same brightness level and they are completely repeatable, even in different sessions on different days, different ambient temp, etc... I'm pretty sure 20 or even 15 seconds would be fine after warmup, but I've been using 30 for so long now it's just a habit.

    As for VC paper with the original bulb. Mine has A LOT of blue light, and not all that much green. So I do all my prints using split grade, with a green filter for the low contrast and a blue for the high. I've read that normal VC filters work but that they can be frustrating to use because the difference between the different grade filters are not even. I decided not to buy them and to go with the split grade approach instead. ( Lots of info here on APUG about split grade printing ). I like it a lot and am glad I'm doing it... It's getting to be second nature.

    I was just about 30 years to get to have a wet darkroom again too... just started up again about a year ago! Have fun!
  3. KennyMark

    KennyMark Member

    Jun 6, 2013
    Holland, MI
    Multi Format
    1) you do not need the variable control, but if you're going to add it, I would buy the compensating timer instead. They work the same, adjusting the time or beeps for the relative brightness as it changes throughout the exposure, but while the variable controller gives you metronome beeps, the timer allows you to set your time and concentrate on whatever you do during the exposure. My mind easily wanders so the metronome is not so good for me. both units have the dry-down feature as well as brightness control to increase your exposure time if desired.

    2) you can use VC filters with either lamp, but will either need to trust someone else's table of filtration and grades, or test to your own satisfaction.

    3) I'm not certain of your question here, or if it is one. Let us know.

    If you're not going to add either the controller or the timer, it's a shame to waste the sensor in the head. As I have one with (Zone VI branded) and one without it (Aristo branded), I'll volunteer to trade my sans sensor Aristo head for yours. :whistling: Just trying to be helpful!

    I've never checked to see which lamps my heads have Ned. Now I need to investigate!
  4. john_s

    john_s Subscriber

    Nov 19, 2002
    Melbourne, A
    Medium Format
    I have a Zone VI cold light head from the late 1970s (4inch x 5inch). It has no transformer, the tube just plugs directly into the 110volt mains. I have a slightly later one for a 2x3 Beseler and it has a transformer. I have no idea why the difference.

    I used a Zone VI Stabilizer, then later a Zone VI Compensating Timer, which has the advantage of being more efficient and giving shorter times. As the tube warmed up the "ticks" of the timer, which represented a nominal "second" of exposure sped up dramatically as the tube brightened. I never actually tried enlarging without either the compensating timer or stabilizer, but the comments above suggest that a reasonably stable light would be obtained by following Ned's advice above.

    I like the cold light head. My prints improved when I started using it. Not that it is "better" but because my negs were too contrasty for my condenser head, as a result of following the manufacturers' instructions for developing (to a highish contrast, maybe to justify advertised film speed).

    I don't know if VC filters will work well with your lamp. Split grade printing (Ned's suggestion) may well be the answer, combined with negatives of ideal contrast to put you in the middle of the range. New tubes with a wider spectrum are available from the company that took over Aristo's business, but they are expensive.* Worth it in my opinion, but see how you go with the current tube.

    Incidentally, in the 1970s I bought two spare tubes from Zone VI but never needed them. They do last for ages. The early ones looked a bit on the blue side.

    *For new "Aristo" tubes see this post. They also make the wide spectrum tubes for single tube units so that VC filters work well.