Cold Light head and 'thermostat' usage

Greetings!

I recently acquired an Omega D-II enlarger for free from a very kind man who offered it up to a good home. The enlarger came with an Aristo Cold Light head (which im assuming has v54 lamp due to it working very well with VC paper) installed and I'm wonder about the usage of the heater part of the unit.

Aristo mentions keeping it running 5-10minutes before usage, and that it "should be left on continuously for the duration of any day or working session."

The wording on that line is a bit confusing to me, 'duration of any day'.

Does this imply it is better or safer to leave it on even when its not in use or expected to be used? While thats not my main question it leads me to what I really wanted to ask:

Is it safe (or suggested?) to leave the heater running overnight or for periods of time I do not expect to use the head? There are times I can imagine accidently leaving the unit plugged in..

What are your habits of use with this function? Any problems or issues youd care to share relating to the thermostat?

As of right now I've been plugging the heater unit in as I mixed chemicals, filled trays found negatives to print etc.. about 10 minutes, did my printing session (usually 2 or 3 hours) then unplugging the heater unit.

Thanks

we let ours warm up as suggested, and then turn them off when done.
as ours is a gang lab and no one is there after class it makes sense to turn off. I believe the directions you are referring to, may be in a commerical setting when people are in and out.

Cold light heads have a tendency to vary light output much more then other types of lamps. This fluctuation is due to not only temperature of the lamp but also minor voltage fluctuations. The reason for this is that cold lamps are inductive types of electrical load and other lamps represent resistive loads. Resistive loads have light output proportional to the input voltage supply. Inductive loads are not proportional to the fluctuations since they have a step up transformer incorporated in their design. This step up transformer increases the input voltage by many orders of magnitude.

Not only should the lamp temperature be allowed to stabilize but also some form of voltage regulation will be beneficial if you want absolute repeatibility. Some years ago Zone VI developed a cold light stabilizer that worked on a feedback signal from the actual light output. These seemed to be the best means of control yet developed. Subsequent to that other manufacturers have developed feedback types of controllers. Metrolux is one such manufacturer.

Donald Miller said:

Metrolux is one such manufacturer.

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MetroLux is the product. It is made by Metered Light, formerly Redlight Ent. It is sold by Calumet or directly, meteredlight.com

The Zone VI stabilizer worked well, but at the expense of brightness. It took about a stop of operating headroom. Closed loop controllers don't require this headroom.

Loose Gravel said:

MetroLux is the product. It is made by Metered Light, formerly Redlight Ent. It is sold by Calumet or directly, meteredlight.com

The Zone VI stabilizer worked well, but at the expense of brightness. It took about a stop of operating headroom. Closed loop controllers don't require this headroom.

Click to expand...

I have the metrolux II timer. It is a hotrod. cannot imagine working with a coldlite with out one.


lee\c

Christopher Colley said:

Aristo mentions keeping it running 5-10minutes before usage, and that it "should be left on continuously for the duration of any day or working session."

The wording on that line is a bit confusing to me, 'duration of any day'.

Click to expand...

No doubt this is referring to a "work day" and is probably directed toward a commercial or institutional user where the enlarger will be used throughout the work day. It sounds like you're doing fine simply by turning it on a little ahead of time as you prep for a printing session. Turn it off when you're done.

As a matter of safety I have everything in my darkroom on a master switch. All equipment is powered down when I'm done. That way nothing is left to chance. I have this thing about unattended heaters.....

thanks for the replies thats the kind of information I was looking for as I havnt really had much experience beyond these past 5 or 6 weeks with a head like this.

I have a Zone VI head, but no stabilizer for it. Can anyone tell me whether the Metrolux controller will work with it, and if so how much it costs, and alternately whether a thermostatic temperature control using the built-in heater would provide stable enough output to avoid using an intgrator or output-based controller? I could pretty easily cobble up a thermostat, but I don't have a lot of money.

the metrolux II has a probe that is also for sale that is used with the Zone VI head. the sensor is placed in the head of the coldlite and reads the lux of the light when the light is on. you just have to ask for it when purchasing the timer. It will add about $30 to the price. This is not a cheap timer. They cost about $350. the advantage to this timer and probe is that it makes the timer and coldlite a closed loop system. that means if anything happens to the power during an exposure and it affects the lite output, this timer will slow down or speed up depending what it needs. to your question, I think that if you cycle your Zone VI head occassionally by pressing expose you can regulate the output and keep it warm without any trouble. Years ago, the first Aristo head I bought had a temp control built in it. You had to leave the head on in the focus mode for about 15 minutes at the start of the session to warm it up. I don't remember if I had to recycle thru out the printing session or not. I probably did not and was probably not told to do so at that time.

the metrolux timer will do several things besides count time. It has memory channels that can be used to store exposure information. With the probe for the coldlite head you can chose real time or Lux mode. Lux mode is influenced by the light that the probe senses and is really UNITS and not seconds. there are 2 Lux channels and 3 sub channels in each Lux channel. There is the real time mode also and there is a % mode that is programable for dry down compensation. There is 2 buttons that move the digital display up or down. You can speed this up by pressing the up button and and then pressing the other button also. This puts the display into a hyper mode and speeds up things quite nicely. Obiviously the same can happen with the down button. The Metrolux II timer can be used as a shutter checker and a small densitometer. There is another device that allows you to replicate the exposure from a known time to another enlargement size. A foot switch is something I can not live without also. Plus the foot print is quite small and mine hangs on the wall. I use the Metrolux II timer with the two tube Aristo VCL 4500 coldlite head. I am very happy with this set up. If you have futher questions, feel free to ask me, maybe I know the answer. (disclaimer: I have no monetary function with the Metrolux II company just a happy customer)

lee\c

For your Zone 6 head, consider the Stop Clock Vario by RH Designs. It has a light probe and in every way is as good as the Metrolux (I've had one), but with F-stop timing (as well as conventional seconds). I only use the Stop Clock now.

Hmm.

One more time -- I have very little money to spend. $350 is more than I have into my enlarger to date, close to my total outlay on processing equipment in the past two years including tanks, reels, changing bag, etc. It's probably more than I'll be able to spend on my initial supply of paper, filters, and paper developer. If I need a $350 timer to get good results from the Zone IV head, I'll spend $200 to replace the missing condenser glass and reinstall the hot light head, buy a cheap metronome at a music store for $30, and wire up a foot switch for $15; at least I know for certain I can get good prints from a condenser head, having done so more than twenty years ago.

What I had in mind was a way to simply stabilize the head temperature using the built-in, separately powered heater. My head has an output for an integrator or stabilizer, but didn't come with anything but a pair of power cords, one for the light and one for the heater. If it would be adequate to wire a simple thermostat into the heater circuit, which I could do for $25 to $50, only power variations would be an issue for the head, and I can handle those with a $60 computer UPS, I think (I'd have to check if the "modified sine wave" output is actually capable of operating a cold light, but I have no reason to believe it wouldn't) -- though there is the issue of whether a UPS can supply enough current to meet the lamp startup draw (I don't know what the Zone VI draws, but I can easily find out what a UPS can supply).

"to your question, I think that if you cycle your Zone VI head occassionally by pressing expose you can regulate the output and keep it warm without any trouble. Years ago, the first Aristo head I bought had a temp control built in it. You had to leave the head on in the focus mode for about 15 minutes at the start of the session to warm it up. I don't remember if I had to recycle thru out the printing session or not. I probably did not and was probably not told to do so at that time."

well, you asked a question as to how much they cost and I gave you an answer. I am sorry you dont like this answer. In the body of the answer I gave you a way to regulate the cold lite head which may help you and your photograhpy. You seem to want to "geek" the thing up and that is your right. I also went on to tell you some of the other things this time would do. I also never said that you had to have something as well made as the Metrolux II timer to get good prints. That is your statement.

lee\c

Sorry, Lee, you weren't the only one I was responding to -- I mixed in responses to other answers about how my light output would change with this and that. If the light output isn't steady, I won't get consistent print exposures, which means the information from a test strip won't be valid ten minutes later when I'm ready to expose a whole sheet of paper -- and did I mention I'm on a very small budget, such that a dollar a sheet for 8x10 multigrade RC is a strong temptation to continue my existing, hybrid workflow (and buying in larger quantity is practically impossible)?

So no, Lee, you didn't tell me I needed to "geek" the thing up to get good prints -- but that's the gist of the combination of the responses I got. Unfortunately, this head does not have a temperature "control" as far as I've been able to tell, just a heater.

Hmm... Perhaps I shouldn't assume, but actually open the beast up and *see* if there's already a thermostat in there. If so, it'd probably be adequate, barring voltage fluctuations, to simply turn on the heater as soon as I wheel the enlarger into the "darkroom" and let it warm up while I get the trays and such ready.

When I was using an Aristo cold light head with heater, I made sure that the heater was plugged in 24/7.

I think all modern Aristo heads have thermostats. But that won't keep the temp accurate enough to keep the light constant. Years ago I had an Aristo, and used it without a compensating timer. I installed a cheap dial thermometer in the head, with the probe just above the light tubes. I aimed for 100 degrees. If too cold, I turned on focus a few minutes. If too hot, I waited. Not at all satisfactory, but better than no thermometer (I guess). Voltage stabilization isn't the problem. As the tubes are illuminated they get hot, and heat affects the light output. Best solution--get a compensating timer.

It a matter of degree. How consistant do you need it? I use a MetroLux because I couldn't get repeatable highlights with a coldlight without it. A percent change will change the highlight. If you don't care about that, you might get a thermostat to work, especially if you had a fan blowing air around in there. IMO the biggest variable to affect light output is the phosphor temperature. One can cool a tiny spot on the grid of the coldlight and there will be a little dim spot there until that part of the tube warms up.

I know that $350 is a bunch, but you might try to find a used MetroLux 1. Seems like I saw one here for sale a while back for $80. They can be made to plug right into a Zone coldlight.

Give Mr Moore a shout.

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

Okay, $75 is still out of my range (yes, I know photography is supposed to be an expensive hobby -- but I have to do it cheaply anyway, and while I can't cut costs much on materials, I can and must on equipment), but it looks like he's now talking about trades -- I dropped him a line.