Zone VI Enlarger Head (or Variable Contrast Unit) problems?

[RichardRitter]

The bulbs will flicker when they are cold. They need to warm up to around 105 degrees F. I turn the focusing on and mix the chemicals for the paper while the head warms up.

[Tin Can]

Has anyone tried leaving the head on (lit) and controlling exposure with a shutter?

[ic-racer]

The issue with timers and cold lights is called "inductive load" which is higher for cold lights than for incandescent bulbs. Unfortunately my background is math, not electrical engineering, so I don't know exactly what inductive load is

The DC resistance on a transformer can be pretty low. So think of that first positive or negative wave of AC (which is identical to a pulse of DC) that hits the coldlight's transformer when the timer kicks in. The current can instantaneously exceed the steady-state current.

[ic-racer]

Has anyone tried leaving the head on (lit) and controlling exposure with a shutter?

The Omegalight operated that way. They [Omega] made an electromagnetic shutter for under the lens.

[Tin Can]

Good to know, I am going to try that with my 2X3 Federal #269 Cold Light, right after I mess with it as is.

Thanks!

The Omegalight operated that way. They [Omega] made an electromagnetic shutter for under the lens.

[photoevangelist]

The issue with timers and cold lights is called "inductive load" which is higher for cold lights than for incandescent bulbs. Unfortunately my background is math, not electrical engineering, so I don't know exactly what inductive load is . However, there was a post on the APUG site which said that ZoneVi stabilized heads (i.e. the electronics built into the VC head) did not have a big "inductive kick" so that most timers would be fine. In any case, the danger is not to the cold light, it is to the timer. I suspect that the standard timers at the university would be fine, but that's easy for me to say, since if one was damaged, I'm not responsible. But I would try it, I think the odds are strongly in your favor.

As to the ZoneVI Compensating Timer, or the VarioClock, both are luxuries. I used my VC head for several decades before I found a Compensating Timer on eBay. The ZoneVi and VarioClock timers take advantage of the photo sensor built into the VC head. The "problem" with any VC head is that the light from the two tubes is additive. If you have the blue tube on max, and the green tube off, you will have a certain light output (and a very contrasty print). If you keep the blue tube at max, and turn on the green tube, you lower the contrast, but also have more light output. (Somewhat unlikely settings, but I'm trying to explain what is happening.) The timers which make use of the sensor in the VC head adjust the overall intensity so that the amount of light emitted is constant, regardless of the mix of the two tubes.

In practice this means that as you work through the iterations involved in making a print with a standard timer, you have one more variable, the light output from the head. But in practice I never found this to be a big deal, since VC paper also changes its speed as you change grades. So if you find your base exposure, and make small adjustments to contrast, in my experience you don't have to compensate. If you decide that your base exposure is a couple of grades off, i.e. you need to make big changes in the settings of "hard" and "soft," you probably have to tweak your exposure times. (In most cases, setting the hard and soft potentiometers to the same setting, say "F," gives you somewhere around a grade 2 or 2.5, which for properly exposed negatives is about right. You normally aren't making big contrast changes from that starting point. Similarly, if you know your negative is very thin, you would pick a starting point with more contrast, etc. But again, as you gain experience with matching grades to settings, you find you are not making huge changes once you have a base exposure you like.)

I just realized that I'm being too wordy. Here is a great chart on VC settings vs. grades: http://www.bnimages.com/files/zonevicontrast.pdf

I attached an LPL Enlarging Timer (ET-500) which is capable of up to 500W and has three prong plug inlets. I'm happy to report that the green and blue lights seem to be working. I've figured out how to work this cold head now.

Thanks for the link for the VC settings, that will prove to be very useful.

[photoevangelist]

Make SURE you do an illumination field test with an empty negative carrier and a piece of paper. Zone VI heads don't seem to age well and you get light corners, light bars down a side, CONTRAST change across the head!!! I had one that printed soft in one corner....pretty crazy to diagnose that! My Type II head is useless. Tubes are gone and the color varies across the face. , Plus has light corners. It was a brilliant conception and certainly pushed the technology forward, but you may have one that won't print.

Friend of mine was printing 4X5 OK on a Zone VI Type I, (not a VC head). When he went to 5X7 it had all kinds of problems. We ran a field illumination test and the head was unuseable except for the center. He sat an Aristo VC 5X7 head that I had on top and it's working MUCH better.

I just switched to a Modern Enlarger Lamp 5X7 LED head on an old Omega E6 Chassis. Cemil used the warm LEDs so it works pretty well with filters. Best printing head and near perfect in field illumination test.

Field illumination test: Put a neg in, focus at full coverage for paper size, remove neg. Stop down at least midway and make a Zone VI or lighter solid print. Don't print it down or you can't see the tonal changes. Process normal. Ought to show dark/bright spots, edges, light bars, et. May also show dust on TOP of your diffusion glass!

If Cemil, or someone, starts doing conversions of Zone VI heads to warm LEDs....they are going to have all the work they can do.

Attachment 112742

I will look into this. You're suggestion has me questioning the illumination now.

This is a photo to represent the light source on after 5 min. I've left it on "Focus" on the variable contrast control. It the light automatically cut off around 10-15 min. later.



I would love to have an LED head. I haven't used a cold head yet, so I haven't experienced the mysticism of the enlarger yet. I've been looking forward to it. The fact that the bulbs are no longer commercially available also lean towards an LED head. I've read about a variable contrast head by Cemil as well. I was under the impression there were a lot more hours on this enlarger so I figured I'd use them up first. If I'm looking at a lost cause with my head and illumination, I may look into converting this enlarger head to LED instead. There are not a lot of "lightweight" 5x7 enlargers. I was interested in this enlarger so I can enlarge my 5x7 negatives.

[photoevangelist]

The bulbs will flicker when they are cold. They need to warm up to around 105 degrees F. I turn the focusing on and mix the chemicals for the paper while the head warms up.

Brilliant. Thank you, Richard. The green "Ready" light was on as soon as I plugged it in. I had the light source on "Focus" until the light automatically shut off around 10-15 min later. Even after it shut off, the Blue (Hard) setting would flicker. After posting a few replies, it no longer flickers. I'll keep this in mind to wait a bit longer and set chemicals up first.

I guess the next logical step is for me to try Robert's suggested illumination test.

[Paul Hoyt]

I found the Zone VI compensating timer to be more trouble than a good Gralab digital timer. With the compensating timer you can NOT split print. I have found using the hard and soft controls to find the approximate printing contrast can then be refined by split printing. Usually, I print for the highlites and adjust the hard setting for the shadows; 30 second exposure with "soft" @ G and "hard" @ F. Then I print with the "soft" only ["hard" off] for 30 seconds; turn off the soft, turn on the hard to "F"; make a series of increasing 4 second exposure across the print to see how many seconds of "hard" exposure will give me the proper shadow detail; it may be 24 second, or 36 seconds, your eye will tell you which exposure is the best exposure. Compensating exposure timers adjust the time intervals according to the lamp output; if the "hard" exposure is 1/2 the lamp output when they are both on, the compensating timer will double the time when you print with only the "hard" or "soft" lamp on.

[Ron McElroy]

I found the Zone VI compensating timer to be more trouble than a good Gralab digital timer. With the compensating timer you can NOT split print.

I had no problem split filter printing using a Zone VI timer. Instead of thinking in absolute seconds it counts in units of light. I now use a Stop Clock, but it is the same principal.