Hue variations with BW400CN on RA-4

Discussion in 'Color: Film, Paper, and Chemistry' started by Michel Hardy-Vallée, Sep 13, 2007.

  1. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    So now that I can print RA-4 at home, I decided to use my BW400CN for what they were made for, namely RA-4 printing. First reaction: blimey! they are nice, no grain, and smooth tones. It's weird to have an entire colour chain but to produce shades of gray in the end, but "toning" is much more simple :D

    Second reaction: why is it that certain areas of my print have a cooler tone than others? Anybody ever noticed something similar?

    It's hard to tell whether it's related to densities. I would suspect that different shades of gray may vary in apparent hue. After all, color dyes are not perfect. But I'm wondering if that would be related to processing instead. I'm sorry I can't post a scan right now, but I'll try later if I can make it visible. I'm confused, and I wonder whether it's metamerism playing a trick on me.

    I'm using Supra Endura in Kodak chems, processed in a Unicolor drum on a motor base. I use a stop bath between dev and blix.
     
  2. boyooso

    boyooso Member

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    color crossover /-)
     
  3. Discpad

    Discpad Member

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    It just indeed might be a bit of metamarism from the dyes: What kind of light (sun, incandescent, fluorescent) are you viewing the print with?

    Also, if you develop your own C-41, the orange contrast mask may be slightly "off."

    A better workflow for you, if you like chromagenic film, is to try Ilford XP2 and use conventional B&W paper... It allows you to use fiber prints, too!

     
  4. bob100684

    bob100684 Member

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    this is something I noticed when working with bwcn on an optical minilab as well! I think there is crossover with this film. Also do your filter settings change with over/underexposure? Ours did at the minilab.
     
  5. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    Yes, the colour balance is noticeably different with exposure. What is colour crossover?
     
  6. Discpad

    Discpad Member

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    Film exposure, or exposure of the paper? -- Be specific.

    Color crossover is where the three (red, green, blue) curves do not align, but instead "cross over" each other.
     
  7. bob100684

    bob100684 Member

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    Its been a few months since I worked at the lab, but it was the film's exposure that varied the color cast on the print. We were confused at first b/c we color corrected to make them neutral on the monitor, finally we turned off the accs which makes descisions on basline color corrections for how things will appear on the print processor's monitor and sure enough there were differences between under neutral and over film samples.
     
  8. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    OK, here's what I noticed: from the same negative, prints exposed at different times have different colour balance. For example, the one at 14secs @ f11 has a more cyan cast than the one at 9 secs @ f11. That part is not surprising to me.

    What is surprising, on the other hand, is that on the same picture, the one I printed at 10secs @ f11, say, some parts thereof are more cyan, and other ones are more red.
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    Well, there are two thoughts that come to my mind here. The film itself cannot have crossover per. se. It is a single layer film with a 'black' dye former.

    The paper can have crossover or reciprocity. You may be seeing reciprocity, but that is an awfully short exposure time over which to see such a color shift. In any event, with color, you keep the time constant and vary f stop, not the other way around. This eliminates reciprocity.

    Also, process variations can cause both crossover and color shifts. If you are not using a steady temp, time and a good enlarger with transformer, you can get shifts.

    PE
     
  10. Bob Carnie

    Bob Carnie Subscriber

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    Michael
    I would not worry too much re the crossover, It is natural occurance printing this way.
    You will find the more contrast range on the original negative the more *cross over* you will see .
    To get less *cross over* a flatter negative will be very helpful.
    This is the same problem printing scala on Ciba material. the flatter the original image the better nuetral can be achieved.
    I do not think you are doing anything wrong, just your negative may have too much contrast.
    You can take advantage of this *cross over* problem with time and make negs to look a certain way on colour paper.
    Trying to get a nuetral step wedge on colour paper from a silver step wedge is one of the most difficult tasks one can imagine.
    If you do a colour ring around on paper from a negative, less exposure with identical colour balance will give you a more cyan cast, more exposure with identical colour balance will give you a more red cast.
    Bob



     
  11. Photo Engineer

    Photo Engineer Subscriber

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    Bob;

    A change in color balance is not normal for Kodak paper. It should not happen, otherwise color balance would shift constantly.

    If it does, something else is going on.

    PE
     
  12. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    Thanks for all the suggestions.

    PE -- most of my printing times are between 10 and 17 seconds, and I don't change time after I get the densities right. But I'll stick to one time + aperture change, given that I have enlarging lenses with continuous aperture.

    I will look on the side of my processing, though. My temp control system is the tap, but at least I have an accurate thermometer. I have a Unicolor drum, and it's not as sharp as a Jobo system.

    Bob -- I'll try the step wedge. I have both a projection wedge and a contact wedge. I noticed indeed that getting a nice balance between the cyan and the red is touchy. This particular negative is indeed contrasty, going from a shadow to a light source.
     
  13. Michel Hardy-Vallée

    Michel Hardy-Vallée Membership Council Council

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    Oh, I've used XP2 on silver gelatin, but for the present exercise I was interested in getting a "neutral" gray (as far as that is possible) on colour paper. Given that BW400CN is designed for colour printing, I wanted to give it a shot, and see what look it can produce.
     
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  15. Bob Carnie

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    Sorry Ron
    But I have made colour ring arounds in every Lab have worked at for colour correction purposes, this date backs from 1976, with basically all the offerings that Kodak produced , Agfa and Fuji.
    If you take a normal negative and get a perfect balance , and then do a density change only you will notice that the darker print has a red cast and the lighter print has a cyan cast.
    In fact this hold true for inkjet colour ring arounds as well.
    That is why all experienced colour correctors will get density first before adjusting colour. This is a common fact with colour correctors. Try a ring around on any normal negative with a full colour range and unless one is colour blind this shift in colour is present when the density is off proper balance.
    The very first thing that I would teach any potential colour corrector is to do a colour ring around which includes density, so that they can see this very effect.
    The problem Micheal is experincing or notice ing is classic problem of silver negative on colour emulsion, and not an imbalance in his process, unless of course he is not following proceedures.
    This imbalance is why Harmon has introduced the new RC and Fibre paper so that photographers can choose a dedicated black white paper rather than trying to mimic Black and White on a colour emulsion.

     
  16. Photo Engineer

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    Bob;

    I have only done this kind of work since about 1961 in production at the Cape and later research at Kodak. It was all very carefully controlled with constant times and varying just f stop for density. I have found that color balance stays the same as density varies.

    In fact, I just did a series from f5.6 - f22 at 12" with Endura and had neutral scales in the scene and had no problem. I processed my own film and paper and I did it with Portra 160 VC and Portra 400 VC. It was an exposure series from ISO 25 - ISO 1600 on both films.

    So, if you do see crossover or shifts, I have found either the film or paper has had a variable process. Either that or the film or paper has a crossover problem (very rare) for one reason or another. I have seen crossover in both film and paper though, but it would be rare for these to get by QC at Kodak.

    So, I guess my experience over the years differs from yours.

    Remember one thing though that might mitigate this. The 'professional' papers made by EK has a soft magenta toe to prevent having blue-cyan highlights. If you darken a print, it will have a less cyan cast than the lighter print (opposite of what you describe) as you move skin higlights up off the toe. Lighter objects in professional papers tend to be pinker than those in photofinishing papers. This is a deliberate design feature.

    PE
     
  17. Bob Carnie

    Bob Carnie Subscriber

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    Ron
    You are right our experiences are different.

    I am looking at a ring around in my colour correction area and I do see a red cast on minus 30 density or 1 stop, as well I see a cyan cast on a plus 30 density or 1 stop.

    Why this is so I am not sure but it has been a consistant for my whole printing career in many colour shops.
    The technical aspects I will leave to the experts at the manufacturing plants, but asthetically when colour correcting this has always been the case no matter what paper stock being used.

    Cross Curve issues were very prevelant with interneg materials and I spent many hours banging my head calibrating and interneg emulsion, 6121 and the dreaded 6118.
    We used dye step tablets over silver step tablets and used three different methods to try to balance each emulsion.
    In the end plotting got you close and then doing a interneg of a grey background that was lit from white to black in an even gradation was the defining way of seeing the cross curve. It always showed itself in the transition from highlight to shadow.

    I think Micheal is seeing that difference that you suggest as being an inherent part of the design of the paper.
     
  18. Bob Carnie

    Bob Carnie Subscriber

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    Ron
    I just reliezed that I mistakenly mentioned the wrong code numbers so before you slap my wrists, 6121 and 6118 are transparancy films which I used along side their equivialants in interneg film for making multi image photocomps before the introduction of PS. I forget the code numbers for the negative material but do not forget the grief they gave me balancing in for nuetral tones.
    The transparancy did not have anywhere near the problems in balancing that the interneg to colour paper did.

    The trans were used to go for advertising and usually were scanned rather than printed from the composite.
     
  19. Photo Engineer

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    The internegative films were notorious for difficulty in printing.

    They had an upswept shoulder to compensate for the toe in reversal products and if you didn't hit that upsweep just right, things went bad. Also, reversal films have a bit of crossover built in, as you can see from the "G" series on Kodak's web site. This gives a 'warm glow' to slides. Kodachrome dupes are very hard to make and give a very bad over-under color shift.

    So, if you are talking about prints from slides via any interneg, I agree 100%, but otherwise I would have to agree to disagree.

    You must admit that a 30 color shift is a bit much. One stop??? That is just not permitted. Kodak's limit was under 0.1 log E. I forget the aim release value, but it was pretty small.

    PE
     
  20. Bob Carnie

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    Hi Ron

    No , I meant a noticable colour shift with a stop shift in density not 30 pts of colour, actually it is noticable with a 5D change *30d change equals 1stop change, my ring arounds are all done with 2.5 colour differences and 5D changes.* I am also talking subtle colour changes that maybe are not significant or obvious for some work that is heavily biased in one direction*
    Kodak manuals back in the 70's described colour ring arounds and I have sworn by them as colour guides and am totally not embarrassed to use them.
    They are really significant when you are trying to tell the difference between colours that are mixtures of two colours for example*yellow green is hard to distinguish from green or even green cyan* with a properly executed colour ring around in your working space these different colour casts are easy to pick out.

    BTW I am really quite glad that I never have to work with internegative film again.

     
  21. Photo Engineer

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    The color ring arounds are quite familiar to me. We had to make some of those to illustrate the use of new papers or films.

    If you wish, I could post some of my results, but I would add that with some work, I have been able to make internegatives that match camera film exposures with no problem. I do it on-easel with the appropriate color balance. For Portra 160 VC for example, I use 100C and 30M and do a 15" pull C41 and match exactly the in-camera exposure of the same film for color balance.

    I guess I don't follow your color shift information as it is in terms unfamiliar to me. I would expect the worst deviation to be less than a 10 in c, m, or y. Usually it is less than 5. In the case in point it is in that range.

    I have coated films that failed this test, but they are truly outside of the Kodak release specs due to crossover in the upper scale.

    PE
     
  22. Photo Engineer

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    Here are 6 pictures exposed in camera at 1 stop intervals. I made prints at 12" with my standard filter pack. The only change was in f stop.

    From left to right it is Portra VC 160 at 25, 50, 100, 160, 200 and 400.

    Hope looking at the neutral scale helps.

    PE
     

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    Last edited by a moderator: Sep 17, 2007
  23. Photo Engineer

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    BTW, the above are direct scans of the negative. I have the prints of these as well to post if anyone is interested.

    PE
     
  24. Bob Carnie

    Bob Carnie Subscriber

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    The darkest image, the grey card definately looks red to me as compared to the grey card in the lightest image. yes/no?
     
  25. Photo Engineer

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    If that were so, then the greens and cyans would have become desaturated. I can only say that it is darker.

    PE
     
  26. Photo Engineer

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    Here are the scans of 8x10 proof sheets from the negatives above. Each name indicates the f stop change from 5.6 - 22.

    They were all exposed, as indicated above, at one standard filter pack and 12" exposure time.

    These are all from Portra VC 160 exposed from ISO 25 - 400 and therefore you will have to select the correct exposure of film to match the paper.

    The 160 exposure is at the top (left) of the scene.

    The first post shows the film response as scanned with no changes and this post shows the paper response to the film over the ISO range selected when printed at 1 stop intervals. There is no significant color shift. My conclusion is that one of the B&W dye based films should do as well or better. This is based on myriads of experiments like this.

    PE
     

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