magenta cast in the shadows

Discussion in 'Color: Film, Paper, and Chemistry' started by jbl, Feb 13, 2012.

  1. jbl

    jbl Member

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    I've had a few rolls of C-41 from time to time show a distinct magenta cast in the shadows of the positive (scan). Often, I can correct for a color cast, but it seems that in these cases the darker areas of the frame (corresponding to the thinner areas of the negative) have a different color cast than the brighter areas.

    Since it happens with some rolls and not with others, I'm assuming this is a processing error on my part. Is there any way to know what part I messed up?

    Thanks,

    -jbl

    EDIT: I've been checking my notes on this and I think I may have seen this more with Portra 400 than with Ektar or with Fuji Pro 400H.
     
    Last edited by a moderator: Feb 13, 2012
  2. Greg Davis

    Greg Davis Member

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    Are you maintaining 100 degrees during development? Are you reusing any of the chemicals? What brand chemicals are you using?
     
  3. jbl

    jbl Member

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    I'm using the Rollei kit. In the most recent case, the chemicals were freshly mixed.

    Is it possible to know if my temperature was off or if my development time was too long? Would one manifest one way or the other?

    -jbl
     
  4. frotog

    frotog Member

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    Without running control strips and doing the sensitometry anybody's guess is as good as the next person's. It's very hard to keep c41 in control at a lab let alone a home drkrm.
     
  5. Greg Davis

    Greg Davis Member

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    Kodak recommends measuring the temperature immediately after development to be sure it was at temperature during development. If there is a significant difference between the temperature before and after development, then your control needs to be improved.
     
  6. markbarendt

    markbarendt Subscriber

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    One possibility is a bit of underexposure.

    When you print from the straight line portion of all three curves your color balance is normally either globally good or bad.

    When film is underexposed, you can easily end up printing off one or two of the toes of the 3 color curves. In this case the shadows will show problems and the rest will be okay, or vice versa.
     
  7. jbl

    jbl Member

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    Thanks for the help everyone. Some more data.... I've seen this with two rolls of Portra 400 I processed myself a couple of months apart with a different mixing of chemicals (same concentrate, just two batches of working solution). I've also seen this with a roll of Reala I shot back in July that was processed commercially at a decent lab (it was at a fairly good local camera store, not at a mini lab). I'm attaching a few examples of this.

    portra-1 is the example from August that I processed. portra-2 is the example from the other day that I processed. reala is the example from July that was commercially processed. Only one of these photos is any good :smile:.

    -jbl

    portra-1.jpg
    portra-2.jpg
    reala.jpg
     
  8. markbarendt

    markbarendt Subscriber

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    The color issues appear to be global not just in the shadows, and given that and the variety of places it's happening, my guess is now that it's in the digital processing.

    Have you asked this over on DPUG ?
     
  9. iranzi

    iranzi Member

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    I want to report similar problems I've been having with Portra 400. No problems with Pro 400H or Ektar (i'm processing Reala later on, we'll see how that goes).
    Only the darkest grays and browns seem to be affected. It's not as drastic as in the above examples, but still, there's quite a bit of violet in places where it doesn't belong. Film underexposure could have caused something like this. But Portra 400 is famous for great exposure latitude, up to ±2 stops shouldn't produce significant change, and my negatives are nowhere near these limits.
    I'm using Fuji 5-liter C-41 kits and Fuji Crystal Archive and Crystal Archive Type DPII papers in Kodak Ektacolor RA4. All Portra rolls in question came from the same box and are presumably the same emulsion batch.
     
  10. Athiril

    Athiril Subscriber

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    Take a screen shot of the scanner histogram of the scan preview (no this is not something for DPUG) this will see relative densities and if there is a problem with exposure or processing.


    But given it's home processing vs your processing with similar results, and the squizzing at the image in an editor and looking, they all appear underexposed or possibly underprocessed (short time, low temp or under replenished), they're unlikey to have the exact same fudge up as you, so I'd guess underexposure.


    If you're relying on your camera to do the metering, take the same exposure readings and put it in a digital camera, or compare it to a light meter if you can borrow one or have one, it should tell you if it's off by a fair bit.
     
  11. Lamar

    Lamar Member

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    I've seen the same in Ektar scans when underexposed. The shadows shift to purple. Didn't matter if I developed or a lab developed. I started shooting to make sure the shadows had enough exposure and I don't really see it often any more. Ektar can handle quite a bit of overexposure. This does bring up a subject I posted on quite a while back about the Ektar data sheet giving exposure settings for ISO 50 film, not it's box speed of 100. If you look at the recommended exposure settings for given lighting in the datasheet it's the same as Velvia 50. Things that make you go "Hmmmmmmmm".......



     
  12. Lamar

    Lamar Member

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    I just checked some of my Portra 400 scans and I see the same purple shift in dark, underexposed areas. It becomes more noticable when you boost the lower end of the tone curve to lighten the dark areas. I don't think it has anything to do with your processing, it's more a trait of the film when scanned. I can't say if the same thing would happen when using traditional printing techniques.

     
  13. markbarendt

    markbarendt Subscriber

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    A color exposure is actually made up of 3 separate exposures, one for each color layer.

    The layers don't always balance so to print we adjust color balance by adjusting the luminance of the layers separately.

    In a typical photo as long as you are printing from the straight line portion of all three layers you can do a fair job of balancing.

    The problem comes when we reach the toes. Since the layers don't always get balanced exposure we skew things to balance the mid tones and then the toes won't balance. The luminance on the toes don't balance at the same place the straight lines do so you start getting color casts in the shadows.