Cold light head output fluctuation

[MarkL]

I've read other threads on this subject but couldn't quite find one that answered my question.

I have an older Aristo D2-Hi cold light coupled with a Zone VI stabilizer, and under the lens filters. I always plug in the heater for a bit (at least 10 minutes) before printing. I’m working on a split grade print that is mostly grade 5 and two identically processed prints are varying significantly in brightness. The second print is lighter than the first and was done some 10 or 15 minutes after the first. I understand that light output drops as the fluorescent tubes get warmer, but isn’t the Zone VI stabilizer supposed to account for this? The stabilizer is only set to brightness “G” and the green “stabilized” indicator was of course always lit.

I realize grade 5 is going to reflect small changes in light, but this is in excess of what I would see in a normally exposed print vs. one with 8% dry down dialed in. I notice that the top of the head is very warm to the touch, so I’m thinking of simply not using the heater and just preceding each exposure with at least 30 seconds of “on” time with the lens cap on immediately before exposing.

I’m a little disappointed in the apparent false stabilization of the stabilizer. Does anyone have a solution or recommendation?

Thanks!

Mark

 

[AgX]

I understand that light output drops as the fluorescent tubes get warmer, ...

To the contrary. Fluorescent tubes need some time to reach their maximum output.

 

[gorbas]

Years ago when I occasionally used cold light source I could notice the very same problem you are experience now. I think somebody (Zone VI?) made cold light source with photocell measuring output and compensating with + or - exposure time.

 

[MarkL]

To the contrary. Fluorescent tubes need some time to reach their maximum output.

Yes, they warm up and reach a steady light output, until they get over warmed and the light output diminishes, as I understand it. But why isn't the stabilizer compensating?

 

[AgX]

That overwarming is not a behaviour fluorescant tubes show on a regular ballast.

It seems to me (without knowing that head in detail) that the feed back circuit of your "stabilizer" is out of order.

 

[Steve Goldstein]

Have you tried plugging in the preheater an hour or two before you start printing, rather than the ~10min you mentioned before the first print?

What happens if you expose two prints one right after the other, then process them serially? Do you still get as much variation?

Here's another idea. I don't know if it's really a possibility - it could be a red herring...

Do you know which bulb is in your D2-HI? The newest one, the V-54, is best suited to VC paper. That's what I have in my Zone-VI-stabilized head, and I've never encountered the issue you describe. Is it possible you have the older bulb (W-55??), and if so, is it possible the color is changing with extended warmup/use even though the total light output is stable? I don't know how you'd test this without some kind of spectrometer

 

[MarkL]

That overwarming is not a behaviour fluorescant tubes show on a regular ballast.

It seems to me (without knowing that head in detail) that the feed back circuit of your "stabilizer" is out of order.

AgX, please see this old thread:

(there was a url link here which no longer exists)

Although it is for a W45 lamp, it shows a graph of diminishing light output as the lamp warms.

"This graph shows the light intensity of the W45 lamp (as measured from a light meter on the baseboard) as a function of time. Per Aristo's recommendations, I limited the test to five minutes. The housing and lamp were pre-warmed with the lamphead's built-in heater. This response (the decrease in intensity) is alluded to on Aristo's website, but its magnitude is not indicated. As you can see (the blue line) the intensity drops one-half of a stop over five minutes, with most of the drop in the first few minutes."

 

[Robbie Bedell]

Mark, I have the newer V-54 lamp and a Zone VI stabilizer. What I have found is that the lamp 'wants' to be used. If I go for long periods without printing with the big enlarger the lamp will sometimes flicker during an exposure. Then, the more I print and the more the lamp is used the flickering stops. Do you use the lamp often? I have found the best thing to do is turn on the lamp now and then and let it heat up and the just turn in on now and then to 'wake things up.'

 

[Bill Burk]

I've marked "G" on my Zone VI stabilizer as the "highest" mark that's stable. Maybe your system is like mine and you are just running at the upper limit of brightness that can be stabilized.

 

[MarkL]

Mark, I have the newer V-54 lamp and a Zone VI stabilizer. What I have found is that the lamp 'wants' to be used. If I go for long periods without printing with the big enlarger the lamp will sometimes flicker during an exposure. Then, the more I print and the more the lamp is used the flickering stops. Do you use the lamp often? I have found the best thing to do is turn on the lamp now and then and let it heat up and the just turn in on now and then to 'wake things up.'

When I get home I'll try to determine the lamp inside. I got it used off the auction site several years ago. I do use it often and I mostly plug in the pre-heater more than 10 minutes before I print...often a lot more than 10 minutes. What I assume happened is that it warmed up some and stabilized for the first print. Then by the time I printed the second print, the heater had been plugged in long enough to get even hotter. Like I said, the head was quite warm after the 2nd print. I'll try taping a thermometer to the top of the head and monitor the temperature.

Bill Burk: My zone vi stabilizer shows a green light just fine up to I think M or N!

 

[AgX]

Mark, thank you for the link to that old thread.
As said that behaviour is completely different from normal at a standard luminaire.

It all depends on what is actually in that magic housing. There is another old thread about that thingy and seemingly back then nobody knew how it looks from inside...

 

[AgX]

Mark, thank you for the link to that old thread.
As said that behaviour is completely different from normal at a standard luminaire.

It all depends on what is actually in that magic housing. There is another old thread about that thingy and seemingly back then nobody knew how it looks from inside...

 

[AgX]

Mark, thank you for the link to that old thread.
As said that behaviour is completely different from normal at a standard luminaire (be it with ballast or electronic regulation).

It all depends on what is actually in that magic housing. There is another old thread about that thingy and seemingly back then nobody knew how it looks from inside...

 

[Bill Burk]

MarkL,

Maybe it's just that Grade 5 is sensitive as you first said...

But maybe... That photocell is looking at just one piece of the tube... take a look and see if the small segment of the bulb where the photocell is aimed is brighter/darker/wavering compared to the main front part of the bulb...

 

[Luis-F-S]

I’m a little disappointed in the apparent false stabilization of the stabilizer. Does anyone have a solution or recommendation?

Thanks!
Mark

Sort of why I used a compensating timer like the Metrolux or the newer (though much more expensive) RH design timer. They compensate the length of the time (seconds) to account for light intensity fluctuations caused by bulb temperature. Works much better than trying to dim the light slightly in order to "stabilize" it like the Zone VI stabilizer did. If you can get one of the older Metrolux or another compensating timer, I'm sure you'll be quite pleased with it.

 

[ChuckP]

Have you tried to run the print using a stabilizer setting higher than G? Maybe you are running close to the edge of the system operating range. I run my stabilizer at K with the D2-HI V54. Works for me but I very seldom use a grade 5 filter. Also as mentioned you could try changing the position of the sensor in the head.

 

[paul ron]

turn the light on for a few minutes before printing... and leave the heater plugged in.

the time it takes to focus and compose should be enough to get the tube to max output just before you get ready to expose.

 

[ic-racer]

The thermostat heater in my 1414 kept the housing about 39C. It did get hotter when the lamp was on and dropped 1/2 stop output after 5 minutes of continuous lamp ON time.

 

[ic-racer]

With lamp behavior like that, split grade printing was nearly impossible to refine. However, a simple Ilford MG filter holder solved the problem, eliminating the need for two exposures.

 

[Mainecoonmaniac]

I haven't done split grading with a cold light head before, but I've heard the bluish light is not fully compatible with VC paper. Isn't VC paper's sensitivity made for tungsten 3200°K light? Maybe you should switch over to a tungsten bulb head?

 

[ic-racer]

Depending on the cold light lamp type, the Ilford filter set may lump the contrast range toward the high contrast end (that is #3 not much different from #5). This can be somewhat remedied by a Yellow filter.

 

[ic-racer]

In terms of split grade, two-exposure printing. I got a range of ISO(R) from 45 to 190. Emphasis on the blue end of the spectrum requires a certain precision in determining the blue exposure time. That is, small changes in blue exposure can have big effects. It also follows, that small changes in cold light output during the blue exposure, can have very noticeable effects when comparing test prints to final prints (where is the 'knocking head on wall' emoticon...)

 

[MarkL]

Everyone...thanks for your generous help. I took a closer look at the head and it's a Zone VI and I labeled it d2-hi. So being Zone VI it should have an officially installed light sensor inside, but the bulb could be ancient! I still need to have a look at where it's aiming and also see if I can tell if it's the newer bulb or not. Meanwhile, last night I printed again, this time never plugging in the heater. For each print, just before exposure, I turned on the light source for 30 seconds. The results seemed more consistent. The second was slightly lighter. I should mention, that this was for 8x10 size and I only mixed the 1+9 Ilford multigrade developer to 1 ounce + 9 ounces for the two prints and developed each for a full 3 minutes. The prints are not dark, and I calculate that 1 ounce of developer should be enough for 3 prints. 1 liter (33.8oz) does 100 8x10's, so 1 oz. should do 3 8x10's.

ChuckP: Maybe I better try a higher brightness setting, although the unit should show a red light if it's not stabilized!

This is frustration that "non-analog" printers don't have to worry about. How boring!

 

[john_s]

The original tubes in the Zone VI single tube head back in the days when good paper was graded paper had a large increase in light output as the tube heated itself. Having the internal heater switching off during exposure did little or nothing to stop this. The Stabilizer, or later the Compensating Timer, made a huge improvement in consistency.

Some (maybe all) newer tubes* are different. In my case, I have a two-tube Aristo VCL4500 and the light output actually decreases as the tube gets hotter, like ic-racer's post above. A compensating timer is still worthwhile in my opinion but it's not as critical as in the old days, especially if you can get into a rhythm of on-times and off-times.

* by "newer tubes" I mean the ones that have a wider spectrum. The original ones were rather blue and suited graded papers well.

 

[AgX]

If someone knows the basics of that regulator inside that box, I would like to know. I never bothered with such head, but this thread made me curious due to the peculiarities of that thing.