aristo cold light question

Hi ,

I recently acquired (for free!) an aristo D2 cold light. I'm sure it’s moderately ancient (product# 3 026 410). It does work, although with a HALTING lack of consistency in print times (as in stop printing right now before you waste another 10 sheets of paper!). The same print time will yield wild variances in print brightness. Once when I took off three seconds, the print went even darker! I've had my challenging print sessions, but this is ridiculous! Time for a beer.

My home darkroom is under construction, so I've been using the college darkroom, now that all the students are away. The enlarger draws power from a designated transformer which regulates the voltage @ 120V. Would an additional voltage regulator be required to keep the light constant? Would this explain the problem?

The other question revolves around that other mysterious power cord that appears to do nothing at all. I believe this is for the "thermo”. Can someone explain what this is, how it works and how it might be contributing to the problem?

Any other ideas? Replace the tube?

Thanks!

CJ Jordan (troy)

The cord helps keep the temperature consistent. Cold lights need to be kept at an elevated temperature to produce repeatable results. I had the same problem with mine until I figured out what that odd little extra cord did. There could be other problems but I'd bet plugging in the thermo will get you where you want to go.

Cold light tubes change intensity as they warm up, thus print exposure changes.

If you were to make successive prints with no processing time, all except the the first few would be the same. If you fully proess each, say a four minute process, and make a new another print, it will be the same as the first.

The Aristo dimmer runs the tube at a reduced voltage thus minimising start up to end of print variances. It is a variable dimmer and you can reduce the light up to threee or four stops.

The themal cord plugs into wall ac 110 volt and warms the tube so start up and run light output are more the same . 15 minutes required to fully warm up.

High inductive loads at start will will slowly destroy some electronic timers. The Aristo contactor is a relay designed to isolate the timer and cold light.

Another way to work is turn the lamp on and use a mechanical shutter or cardboard and metronome timer to make the exposure. Do not turn off between prints. Consistency will be as perfect as your timing.

Any diffusion head will make the same prints as a cold light. The whole thing is a pain unless you want to experiment.

A compensating enlarging timer (like one made by Zone VI or Metrolux) will use a photo-diode inside the lamp housing to compensate for brightness changes. It works and delivers very consistent results. Any cold light can be modified to work in such an arrengement.

The best bet would be to use a compensating timer. From what I can see, Calumet no longer offers the Zone VI compensating timer. They appear to have one 220volt version available. As of a couple of weeks ago, they no longer had extra sensors available, although they claim they stillplan to carry them. I have the Zone VI timer, and I like using it. But from what I've read, the Metrolux is probably the better timer. There are sensors available, etc..

As far as whether or not to use a stabilizer along with a compensating timer, you might give Aristo a call. (See www.aristogrid.com.) They provide good technical support.

Take a look at RH Designs StopClock Vario.
http://www.rhdesigns.co.uk/darkroom/html/stopclock_vario.html#note

It has a light sensing probe that is mounted under the cold light. The timer reads this and modifies exposure to compensate for the amount of light output. Consistent printing is then the norm. I have an Aristo 12x12 head on a Durst 138S converted to process 8x10 negatives. The timer has many other advantages. Go to APUG.org and search on RH Designs for more detail and user reviews from others.