Halogen lite ramping -- how to deal?

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jstewart

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Folks,
I recently began using a color head with halogen light source.. previously I'd been using a cold lite head.

With the halogen source, I notice there's a significant amount of time that the lite takes to completely "die out".. maybe half a second or so.

This is interfering with my practice for translating test strips to final exposures. My test strips are done like this: I cover a segment of paper and expose it.. then trip the switch on the timer to cease the exposure. Then I move the mask and turn the timer back on to expose a wider strip.. etc for 4-5 strips over a 30 second or so total exposure to the first strip. This means that all the strips actually get measureable additional exposure due solely to the ramping of the halogen lite, with the greatest effect on the first few strips.

I think it makes a difference because my draft print, exposed with the best looking test strip, looks very different than the test strip I used to estimate the exposure.

I guess I could remove the effect of the ramping by using a card to obstruct the light path at the designated time, but I was wondering if others have already dealt with this problem, and how.

Thanks in advance.

Jim
 

Nige

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I've experienced similar 'frustration' but it's never been that much of a difference that has caused me to much grief as I usually do a final test print (small piece of paper) as my choosen time and filtration settings before using a full sheet of paper.

An alternative exposure method is too use multiple 'shots' of a set time. So if you did a test strip you might give it 5secs, another 5secs, etc, then when selecting your time, you expose the print in the same manner, shots of 5secs, that way the paper gets the same amount of lamp ramping as the test strip did.

Edit : forgot to add, ignoring the lamp ramping could be an alternative for reducing exposure for dry down... :smile:
 

Neal

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Hi Jim,

This has always bothered me. I don't know if it matters, but I have made a set of carboard slats. I expose each test strip separately for the time desired. Probably unnecessary, but it makes me feel good.

Neal Wydra
 

Dave Mueller

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I leave the enlarger on for the entire set of test strips, and slide the card when the timer beeps. I wrote a quick program for the old Radio Shack Model 100 "laptop" to use as my enlarger timer, it beeps in f-stop intervals. The first time, in full stops (eg 16-8-4 total seconds), the next time through in 1/3 stops between what I feel are the best full stops. When the timer beeps, I just slide the card over a little. The lines aren't perfect, but I figured that by leaving the bulb on all the time, it would prolong it's life a little. I never noticed any problems with the bulb dimming when turned off, but I try to get most of my exposures in the 16 to 32 second range which is large in comparison.
 

David A. Goldfarb

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I leave the light on for the full time and slide the card like Dave does but using the timer's metronome to time the segments.
 

Bob F.

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I do a hybrid... I use a metronome to time exposures and use a black card to interrupt the enlarger light to start/stop the exposure as you suggest, but use my notebook PC to calculate the fractional f-stop times for each individual exposure - you can easily time to the nearest 0.5 second this way.

Without the computer you could use a table of the type that has been published in a few books (there must be one on the Web somewhere) but this would be difficult to read in the dark... my notebook has a safelight screen over the display.

The only way to really deal with it, I would guess, would be to use a computer based timer that can be calibrated to allow for the ramping - I've no idea if such a creature exists, but if it doesn't, it should...

Cheers, Bob.
 

nolindan

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I tested for the effect of progressive exposure Vs separate exposures with the simple experiment of making a test strip each way and then comparing the two. I did 12 strips at 1/10th stop intervals with a 5+ VC filter. I could not see any difference between the strips. I was rather amazed. The equipment was a Beseler 45 MX, standard GE 212(?) enlarger lamp, Ilford MG IV and an f-stop timer of my own design.

I would suggest making two strips with your setup and comparing the two, as I am sure YMWV.

Shameless plug for an f-stop timer kit: http://www.nolindan.com/da/fstop/kit/
 

Wally H

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I use a kodak step wheel so it doesn't matter....
 

stevewillard

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I have also noticed the ramping, but have found no difference between the test strip and the final print. The test print has proved to be a good predictor for densities in the final print. Perhaps color negative papers are less prone to halogen ramping.

You may want to also try stopping down to reduce the level of light. Ramping under lower light may have less effect. Other thoughts that come to mind is the manufacture of the lamps. The characteristics of the lamp may vary from manufacture to manufacture. The power source may also be part of the problem have longer than usual ramping up and down times. It could also be a faulty voltage stabilizer as well that is causing the problem. Run two prints back to back using the same exposure and see if there is any difference. If there is then the stabilizer is your guy.

If you could try your papers and exposure methods using another enlarger. If it does not happen then the power supply or lamp is suspect. Try different types of papers. Perhaps some are more receptive to ramping than others.

In any case you should try to isolate and characterize the problem before switching to new printing method. It may be something completely different than what you thought, and thus, requiring a different solution.
 

Maine-iac

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I recently began using a color head with halogen light source.. previously I'd been using a cold lite head.

With the halogen source, I notice there's a significant amount of time that the lite takes to completely "die out".. maybe half a second or so.

After reading your post, I paid attention to this, and sure enough, it does take 1/2 second for the lamp to die out.

However, the reason I've never noticed it being a problem, as I further investigated, is that it's that way all the time. So if I'm doing a test strip with 3 second intervals, each exposure is really 3 1/2 seconds. If I set my print exposure for 10 seconds at full Magenta and 10 seconds at full Yellow, then I'm really giving it 10 1/2 seconds at each. But since it's consistent in all steps of the process, it can be totally ignored. It's just that in your head, you know that whatever you're exposing is getting 1/2 second more exposure than your timer tells you it's getting, but so what? The consistency is the key.

Larry
 

Fotohuis

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If you only want to do B&W printing, rebuild it with Split Grade from Heiland. 100% reproducible: HLX on, shutter open 00 (Y), 5 (M), shutter closed, HLX off.

Further you have in one measurement optimum time and gradation. All sensiometric values are stored in the Heiland console. It is very easy to print directly, without calibration, almost 100% results.

best regards,

Robert
 
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