Kaiser Fototechnik Pro lightboxes used 5000k tubes but a custom formulated proprietary paint for the reflector surfaces that compensated for the spikes and dips in the tubes AND the diffuser.Originally Posted by Drew Wiley
Kaiser Fototechnik Pro lightboxes used 5000k tubes but a custom formulated proprietary paint for the reflector surfaces that compensated for the spikes and dips in the tubes AND the diffuser.
Yes, that's what needs to be done. I had to batch up my own special liner white paint to do that. Nothing is trickier than "white". You also have to understand how specific white pigments age.
There was a little more to it then just special paint. Their boxes were pretty thin so the tubes were very close to the diffuser. So besides 5000K tubes each tube had a 5mm silver stripe down the length of them that was opaque and eliminated a hot stripe the length of the tube when looking down onto the diffuser. Tubes were also extremely high CRI as well.
Yeah, avoiding hot spots in thin boxes is difficult. My own critical light box is sometimes used for backlit copy work (LF chromes), so needs to be completely even.
Back to the light over the fixer tray, as I said I look for stains + uneven development, will the whites separate and leave a line between whites and border, and no Dmax in the blacks as the print will be drying down...
The color correction is not critical for B/W as long as the whites are fairly neutral to spot stains etc, but maybe for toning... Color viewing is a whole different matter and much more critical... For B/W, just a light bulb has worked for many for the post electricity period. .. ;-)
Steve K
The problem with b&w evaluation, at least in my case, is the fact that a degree of color (warmness/coolness) is integral to the process, and I am very particular about that with respect to specific images. Then there is the effect of toners, and potentially of split toning. A poor viewing light (like nearly all CFL's) can lead to misjudgment from metamerism. A basic tungsten bulb has a continuous "black body" spectrum without a bunch of spikes and voids to it, so works better. But I never really know for certain until I re-evaluate a complete dry print the following day, when my eyes are fresh (and NEVER after doing something like I am at the moment, looking at a computer screen). Now for some hypocrisy ... I gotta go do a test strip, then a big color print.
I sold Linhof cameras and matched, at the factory, Rodenstock lenses=a lot of both! To what was called a super studio. The studio was owned by a major department store chain in the mid west shooting color catalog shots by multiple photographers all day long, 6 days a week on 45 chromes. Every shooting position had to have matched lenses, lights, light boxes to every other shooting position so that all chromes matched in color as one page might be shot by several photographers at different shooting positions.
One day I visited there new studio which was in a building that had been a former super market. They had Knox light boxes, the great big floor standing ones with two boxes, a horizontal and a vertical one at each photographer’s position so that chromes could be evaluated.
The boxes had masking tape with numbers written all over the illuminated surfaces. Numbers on each box varied widely.
Being curious, I asked why? The answer was that each tape spot showed the variation in K and output across the surfaces from the manufacturer’s spec.
They quickly replaced all of the boxes.
The funny thing was that I was there on a very hot, sunny day. The supermarket had lots of windows that the studio painted black to keep sunlight out and blocked curious bystanders. While we were talking there was a very loud explosion and glass all over the place. The black paint caused some of the windows to explode!
BTW, the first order for matched lenses was for Apo Ronars, but they were shooting three dimensional objects on a flat table and put multiple items on the table to be shot at the same time to be separated by the art department later. But things at the edge just weren’t as critically sharp as at the center. So they then ordered matched Makro Sironars and eliminated that problem.
Depends on the print...
Some are best viewed in total darkness
How I achieve true DMax is to leave the test strip drying about 30 sec too long in the toaster oven. True deep neutral black every time, once you clear the smoke out of the room.
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