There is a warm up and afterglow associated with some types of lamps, most notably tungsten. This increases the red output of the lamp and makes prints more cyan. The longer the light is on, the more the afterglow as the filament cools down.
Originally Posted by jd callow
I use halogen lamps.
As do I in my durst, but I'm unsure of what was used in the Beselers and Omega's I've used.
I have eight 250W halogen bulbs in my head. When I first starting printing I was using all three settings liberally like 90Y 50M 30C and very long exposures were the rule. I had no clue about what I was doing. I burnt out all eight bulbs in less then 6 months. Now my settings are more like 10Y 15M 00C, and I adjust the aperture so that my exposure vary between 5 to 10 seconds. I have not burned out a bulb in three years, and I am printing all winter long.
A lot of things I am noting here are based on memory and observations over long periods of time so the degree of accuracy is questionable. However, I am getting to a place where my sales demand that I can fill orders fast so I need to spend sometime quantifying all of these issues, if indeed, they really exist.
Recently I got a batch of 20x24 Fuji CA paper paper that significantly deviated from settings I have recorded in my database for my master print. I was very surprised. I do have a JOBO ColorLine 7000 color analyzer that I have never used. It has the ability to create a virtual master (VM) YMC setting, and then I can calibrate each batch of paper with respect to changes from the VM settings. These are called batch adjustment (BA) settings and could be recorded on the applicable box of paper. All settings in my database for the master prints would be VM settings. When I would set up my colorhead for a print, I would first set the VM setting and then add in the adjusts for the BA setting of the paper I am using. I think the JOBO will also compute print density setting using the same model. Of course, this is just another idea I will be playing with.
Just for the record I would never recommend a color analayzer for fine-art photography. They are designed for rough production lab work, but used in the manner I just outlined above, they may be a very productive tool.
2,000 watts of lighting, sounds like an 8x10 enlarger.
I don't know what you call long exposures, but in my book a long exposure is one where you set the timer in minutes, something like 5 or 7 minutes for an exposure. This is for mural enlargements using a 10x10 horizontal enlarger.
With a conventional vertical enlarger with 2,000 watts of go juice, unless you were enlarging with a 380 or larger lens at f64 or so, I wouldn't expect anything longer than about 25 seconds, 45 seconds tops, for the size of enlargements you are talking about.
Yes, the lights can go out, when one goes you do have to replace the whole 8 globes.
I would suggest with your reasonably short exposures for a 2,000 watt head, you may be getting minor colour changes due to lamp temperature fluctuations.
The best 2,000 watt tungsten head enlargers, always had a shutter in the head. That way the lamps stay on permanently (so to speak) and when you press the button your integral timer trips the shutter and away you go.
If you place a quite sensitive light meter under your enlarger, place some extra diffusion material above the sensor, then trip your enlarger in total darkness and watch the meter change as the exposure ticks on towards a minute.
I have the original Jobo Colorstar analyser made by Lici, it has a digital readout and I know that a powerful colour head will still be warming up for the first 5 to 10 seconds. In fact all tungsten lamps do, but with a power source as you have the effect can be noticed by paper more easily, than with a single tungsten lamp enlarger
I forgot about the afterglow effect of all of those lamps, it is there, and with 8 globes a glowing
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A friend runs a pro-lab near where I live in the UK, he spent many years as a Durst engineer and he taught me many years ago that to overcome slight colour shifts at different enlargements adjust the aperture to keep the actual exposure time constant. All his printers were adjusted so that the exposure was constant regardless of the lens used, and they did the same with their LF enlargers.
Using this constant exposure time method means that any warm up and after glow is constant, and with older papers helped overcome reciprocity too.
What Ian says is what I also do (or try to do) but sometimes due to magnification I just cannot do it, I have to change exposure time. But, within those limits, color balance is unchanged as is filter pack.
However, there have been many reports of recent deviation in Fuji CA filter packs. I have to assume this is their new CA II paper which uses new emulsions. It was reported on at the ICIS conference in 2006 here in Rochester. Apparently, the filter pack change is not trivial.
Last edited by Photo Engineer; 06-07-2008 at 11:50 AM. Click to view previous post history.
Reason: Bad error in phrasing.
I heard the paper changes were to optimise for digital printing, i.e. lambda & frontier but the paper is now more difficult for optical printing.
Originally Posted by goldie
The changes made it all round better.
Even without afterglow, which most people do have to deal with so it will factor in, you're going to run into paper reciprocity.
A good rule of thumb is to adjust F/stop rather than exposure time, but this will then start to affect sharpness at either extreme of the lens.
I'd say that you'll run into paper reciprocity shorter than 10 seconds and longer than about 60, it'll be minimal within this range.
With B&W paper, I've heard you still get about 1/6 stop of reciprocity every time you double exposure. It will be different with color paper, but probably not too different.
Kodak and Fuji papers have gotten much better than other competitors' (are there any even left?) in terms of minimizing color shift with changing exposure, but IT IS STILL THERE. If anyone would like, I'll post samples. I was using "Ultrafine" paper back in '05, probably rebranded Mitsubishi or Konica or Agfa, and it had very pronounced color shifts with changing times.
The newer papers have probably been heavily optimized for short exposures; there'll be little to no improvements over a minute, as they're working on optimizing paper for quicker exposure in digital machines, and really couldn't care less about people dodging and burning in the color darkroom. If Kodak cares so much about color darkrooming, then why did they discontinue the 5x7 size?