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  1. #1
    retro film's Avatar
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    Are the film specification sheets accurate?

    I feel like theyre not accurate (but they should be, as with any technical data reference). For example, I was looking at the Kodachrome 25 data sheet, and the spectral sensitivity curve for the magenta forming layer seems too low. It seems like with sensitivity that weak for the green layer, any neutral grey objects shot under the correct lighting would appear pinkish due to access magenta dye.

    Can anyone comment on this? are the sheets accurate? Is my suspicion correct?

  2. #2
    Kevin Kehler's Avatar
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    Well, there is two things going on here - one, film manufacturers are using $100k+ machines to make determinations as opposed to most of us who just eyeball it. Second, they generally are testing to a specific standard, one which most of us are not using. So, I have always found ISO speed ratings to be very liberal and found much better to use my own rating for films. I don't doubt the film meets the test criteria but the test criteria are not real world scenarios, they are manufactured scenarios that the real world does not replicate.

    In short, trust the sheets for a start and then develop your own knowledge, based on your shooting style, location in the world, development method and printing style.
    Once a photographer is convinced that the camera can lie and that, strictly speaking, the vast majority of photographs are "camera lies," inasmuch as they tell only part of a story or tell it in a distorted form, half the battle is won. Once he has conceded that photography is not a "naturalistic" medium of rendition and that striving for "naturalism" in a photograph is futile, he can turn his attention to using a camera to make more effective pictures.

    Andreas Feininger

  3. #3

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    The official sheets are very accurate, but determined according to company and industry standards, so you have to learn how to read them.
    and what the implications are for your personal use. You are only partially correct. The greens of earlier Ektachromes were in particular infected with quite a bit of magenta, and Kodachrome was engineered in an entirely different manner; but if you were an advanced color printmaker in something like dye transfer during that era, you knew that you had to do certain things differently with Kodachrome than Ektachrome. Looking at a slide on a proper lightbox or projector, you wouldn't spot anything off. Kodachrome 25 was famous for neutral grays, but sometimes had minor issues with warmer neutrals or warmer "spring" greens. Dye sensitivity in these curves is not synomymous with how that respective hue will actually look in the end result. It's quite a bit more complicated than that. You also have to note at what
    color temperature standard they made these charts to begin with.

  4. #4
    AgX
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    I know several sheets that a wrong. At one company I assume malafide intention (or blatant ignorance) at another ompany I assume negligence.

    Furthermore there are no fixed rules how to make up such data sheets. As result it is often difficult to compare films from different manufacturers.

  5. #5
    Photo Engineer's Avatar
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    I know that Kodak attempts to make their data sheets accurate. It does take some skill in reading spectral sensitivity data, as it depends on the light source used for exposure.

    If the film works though, it works!

    PE

  6. #6
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    Also, who's to say that just because sensitivity is lower in one dye vs another that the dye coupling chemistry won't account for that? Kodak knows what they're doing.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

    http://www.flickr.com/kediwah

  7. #7
    Europan's Avatar
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    Eastman-Kodak had false curve toes with their black-and-white reversal films PXR and TXR. Actually, the entire curve was simply shifted out of the base density of log 0.23 in order to pretend clear lights.

  8. #8
    Photo Engineer's Avatar
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    Quote Originally Posted by Europan View Post
    Eastman-Kodak had false curve toes with their black-and-white reversal films PXR and TXR. Actually, the entire curve was simply shifted out of the base density of log 0.23 in order to pretend clear lights.
    How interesting. Can you show us a reference?

    Thanks.

    PE

  9. #9

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    EK has a reputation for maintaining the highest technical standards and I would hesitate to suggest that they published false data. They have far more to risk than to gain. If I found an inconsistency I would study it further to see if there was some factor which I missed.

  10. #10

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    Can you name another company that has worked harder on accuracy than EK? I don't think there ever were any. When they went under, a world standard of quality was lost.

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