Interneg calibration insanity efforts in process

Discussion in 'Color: Film, Paper, and Chemistry' started by Mike Wilde, Apr 27, 2010.

  1. Mike Wilde

    Mike Wilde Member

    Aug 10, 2006
    Multi Format
    Well, I was born in the mid 60’s, around the time my paternal grandfather retired. He bought himself a modest camera to record special events, like taking himself and Gran on a ship back to England to meet up with his WW1 buddies.

    It was an Agfa Contessamat, in a leather case. The camera was used exclusively to shoot Kodachrome. I never saw it set for other than auto with existing light. For indoor shots it was paired up with an Agfa folding fan flash holder and M2B and M3B flashbulbs. My father would borrow the camera for summer vacations as well. Mostly my dad shot double 8 Kodachrome movies.

    I have inherited a ton of slides, and edited the collection down to about 900 slides and keep them in carousels. Grandpa was no great photographer, and his legacy of a 36 exposure roll would be 5 to 10 keeper slides at best. With him growing up using modest box cameras, the concept of the need to focus was not always remembered, nor the need to move the aperture back to auto after using flashbulbs, when back under natural light. There are rolls that had a Christmas, summer picnics and fall leaves on the same roll, like Gran had to remind him to bring the thing out with them. My dad’s slides are not as poorly shot, but he mostly would use the movie camera and only take the occasional still.

    I can remember this camera being around the house as a tween,, but have no idea what became of it. Mom had bought an Instamatic a few years earlier, when I was perhaps 5, and I was given her old 620 box camera to play with, without film. So I guess the instamatic won out. Mom wanted the memories recorded, but not to have to fiddle with a camera. She is still that way.

    Well recently I have been scanning the old Kodachrome slides to aid my mother, now 86, who is trying to organize a lifetime of shoe boxes of photos and newspaper clippings, and is making quite good progress. There are now summer vacation albums, Christmas albums, a school pictures album for each child, etc. Some years it appears the slide are the only still of an event.

    Seeing these old slides more often has given me a couple of bugs of motivation. One was to get another Agfa Contessamat, and the other was to print some of the slides.

    I found the camera at a camera show a few weeks ago. The leather case is beyond repair, but the camera itself is in pretty good shape. $10 seemed a fair price. The CdS meter still appears to be metering correctly, and so the auto aperture works. The shutter speeds are limited to 1/125, 1/60, 1/30, and B. 1/30 and B are sticky. A wipe of the shutter blades with naphtha on a cotton swab and exercising it has the 1/30 and B working better but not reliably yet. A deeper cleaning will need to be done. I just have not got there yet.

    In the past I have fiddled with duping slide films and have bought up outdated Ektachrome SE slide to slide dupe, and Fuji CDU-II slide to slide dupe, each $5 for /100’of bulk 35mm film. I have calibrated them for use on a Bowens Illumitran to get the exposure and filtration sorted out.

    Printing the slides is a possibility now too. At the same camera show I picked the Contessamat I also picked up for $5 an outdated roll of 100’ of 35mm Fuji IT-N C-41 interneg film.

    This film is tungsten balanced, and Fuji gives little information apart from exposure being recommended at 10 seconds, and local laboratory calibration being required. Fuji says it reacts similarly to competitive products, and should be kept in the fridge, which I had no idea if it had.

    I have not used interneg before. So I set up a calibration rig. My Minolta Autobellows unit and a 50 f/3.5 Macro lens with the slide duper on the rail gives the required optical path. I set up a 20W 12V compact halogen lamp in front of the slide illuminating diffuser to provide a fixed intensity tungsten light source. The tungsten source was switched with an enlarger timer, while the lens was stopped down and shutter held open with the rig otherwise in the black in the darkroom.

    I got out mu copy of Kodak Copying and Duplicating, which is a wealth of technical knowledge on this subject in one manual. It gives extensive information on calibrating Kodak’s interneg products.

    From the book I was able to guess a required starting brightness by metering a grey slide from my Lici analyzer in front of the test rig light source at the same target distance with the camera meter, to give a reading of 1/8 at f/8 iso 125, or something similar to set the lighting level. The lens was then recommended from the text to be f/5.6 at 10 seconds as the first guess. I went with f/4 to account for the bellows factor once the lens went into the bellows for full frame focusing.

    This test rig, when grey slide metered equated to an EV10 value with a 125ISO film speed setting. Quite serendipitously my copy camera lights give an EV or 9+2/3, so once calibrated it should just be a matter of balancing for the different temperature of the copy camera lights to use this film to make internegs from colour copy on my Polariod industrial copy camera.

    The first pass filter pack was what was stamped on the Fuji box, 80Y and 50M, with a 2B UV as Wratten gelatin filters placed upstream of the Macbeth transparency slide I used to calibrate my slide to slide dupe process. Exposures were 5, 6.3, 8, 10.0, 12.7, 16, 20.2, and 25.4 seconds, since I suspected the film may have lost speed since expiring in 2002.

    I processed my test shots in a litre of Kodak’s Flexicolour C-41 developer that Ron Mowrey gifted to me. I hope to use this trial’s test data to better characterize my home brew C-41 developer’s action in the future.

    The density of the grey patches of the Macbeth slide were read in a Macbeth TD-504 transmission densitometer with Status M filters for C-41 film that I was given a few years ago.

    The density data of the 6 boxes of grey on the Macbeth slide for the different exposures were plotted on a sort of a H-D curve as shown in the Kodak copying manual.

    I measured the density of the original slide and correlated the density of the six patches to the equivalent steps that photographing a reflective q-13 or q-14 step tablet copy camera target would give. The steps of a q-13 refection step target I have were verified by making transmission measurements and subtracting the paper base density. The Macbeth slide patches yielded steps equivalent to q-13 steps1, 2, 3.5, 13, and 26 (normally a q-13 stops at 20).

    The plots the first time though showed that I had overexposed on even the shortest shot by at least 1 stop. It also showed that the green layer was plotting below the red layer, and that the blue layer was at too high a density. The curve shape did show a modest upsweep in the highlights, but not as pronounced as the data in the Kodak book suggests that interneg films should have, so I am guessing that the special interneg masking layer dyes are fading as the film has aged or been poorly stored or both.

    I was a bit long on the developer on this first test so the slopes of the density curves were steeper than desired, but I did have images to measure, which made me happy with the first pass results. (The stop bath was in the tempering bottle, and not the wide mouth jug ready for a fast pour)

    On the Macbeth grey target slid patch that is clear the measured negative density was actually a bit less than that for the slightly grey target patch. This is classic overexposure as texts I have read discussed. I have never actually seen show up in data I have measured before, though.

    The second test shot had the filter pack adjusted to cut the magenta filtration density to try to raise the green curve, and add yellow filtration density to try to lower the blue curve. This new pack was 30M, 100Y,and 2B UV. Adjusting for filter pack changes the target exposure was now centered at f/5.6-/f/8 for 10 seconds. Again the same bracketing of exposure times was done.

    This second pass test negatives, after reading the patches negative density, allowed for curves to be plotted. The curves this time around plotted with the red curve with the right step 3 density (about 1.4) corresponding to the 20 second exposure. The blue and green curves for this exposure were plotted. Green was now above the red, but maybe a bit too close to blue, and blue had come down about right, but was maybe still a bit high. I was close enough to make a density difference measurement calculation between the density of steps 3 and 13 as the Kodak manual suggested. I interpolated the needed step 13 density data from the curves. Red and green had DD’s of .77 with blue as .42.

    From the manual I know I want red DD to be a bit lower, green DD to be a bit lower, and blue to be quite a bit higher, if this products from Fiji reacts similarly to what Kodak made. The Kodak book suggests from tables how you can change filter packs to achieve the target density differences , and then to subtract off neutral density to adjust the exposure time. The result of these calculations was that the third round of exposing will be targeted around 12.7 seconds at f/8 with a modest filter pack of 10M +20Y, which I substituted to be 10R +10Y, along with the 2B UV filter to minimize the filters in the image path..

    The results are drying and will be ready to be interpreted tonight when I get home.

    I know that I am crazy to go to these efforts, but also am viewing this as a great learning circumstance. I now know so much more about colour film dye structure, and how to manipulate it. I can see myself using this to figure out filtration on all sorts of strange things in the future.
  2. Mick Fagan

    Mick Fagan Subscriber

    Sep 13, 2005
    Melbourne Au
    Multi Format
    Great stuff doing that.

    In my own case I have used a colour enlarger head on it's side, with a like set-up to yours camera wise.

    By using the colour head I could make very subtle changes and get colour virtually spot on.

    I also used this same set-up for making transparencys from colour negative film using Kodak print film, which is now discontinued, although I still have 4x5 boxes in the freezer.

  3. OP
    Mike Wilde

    Mike Wilde Member

    Aug 10, 2006
    Multi Format
    Mick - Yes, I have experimented with the enlarger head. I have a 'spare' chromega D head to go with my Omega D setup. I wanted a brighter source that was closer to my copy lights fixed colour on the 'process type' polaroid with 4x5 and 35mm backs. Then I know what filters to put in front of the lens, and leave the lights bare and unfiltered.

    The most recent iteration of f/8 20s 10R +10Y pointed to good DD's for red and almost for green (within 0.03 tolerance range), with blue needing a bit more slope. The tables point to -02M and -34Yfilter adjustments. This will result in negative yellow, which is a first for me. Turn my brain to the positive and negative colour wheel:

    M R
    B Y
    C G

    10M + 20Y
    -2M + -34Y
    8M +-14Y
    Add nd 14 units.
    So now it looks like 22M+ 0Y +14C.
    Now next I will figure out the new filter factors for adjusted exposure time.
    I'm getting closer.

    My older (10yo- grade 4) son is quite the young artist. We are running out of space to store his 'good' stuiff.

    The principal at his school is suggesting that he should consider an arts focussed school for senior public, which for us is grades 7 and 8.
    The arts school wants a portfolio to review prior to acceptance. So I think the copy stand will go into service with one dupe film or other to make copies of some of his earlier or oversized stuff, so that we don't have to raise the bed to fit more stuff under it, and still have a page of 35mm or 4x5 transparencies to present as a part of the portfolio.
  4. Photo Engineer

    Photo Engineer Subscriber

    Apr 19, 2005
    Rochester, NY
    Multi Format

    It sounds as if your color balance is off a bit. It is also critical to get the curve right wrt the upsweep. Of course, the film may also be going bad as well.

    I myself use Portra VC pulled 1/2 stop and exposed to daylight on my enlarger (100C/30M) at 1/2" f22 to make a 4x5 from a 35mm negative.