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  1. #1
    David Lyga's Avatar
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    Kelvin & contrast

    There is a difference in contrast when taking pictures under daylight (shade) and indoor tungsten roomlight. When I shoot a roll of BW film under both conditions this situation inevitably manifests.

    Why? I think that it has to do with the bluishness imposing a very slight fog veil over the outdoor image. Even looking at something under the shade, and then immediately placing a K2 (yellow-green) filter over your eye to judge the same scene, shows a slight increase in contrast when using the filter.

    I took photos of a gray scale with color patches under both conditions at the proper exposure. Obviously, the colors imparted somewhat greater contrast with the K2 but the gray scale ALSO did the same. The difference was not much but was at least half a paper grade.

    I prefer the tonal rendition under the lower Kelvin. Indoor tungsten lighting seems to just differentiate the tones better and are actually more believable when printed. It's frustrating to see a roll with negatives with differing contrasts. Are my assessments correct? - David Lyga

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    David Lyga's Avatar
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    I apoligize for the double posting: I was trying to eliminate the % from the first's title and replace it with an ampersand. I was not able to this in edit mode. I thought I had lost the post and reposted with the title corrected. - David Lyga.
    Last edited by David Lyga; 03-23-2011 at 06:51 AM. Click to view previous post history.

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    Wouldn't this have more to do with a given film's spectral sensitivity than haze? Of course, distance is an important factor when outdoors since there is more haze between you and the subject as distance increases, but if you are talking about a subject right in front of you and comparing clear daylight to tungsten I would assume haze to be a negligible factor and instead consider spectral sensitivity.

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    If a film's sensitivity and contrast rendering are different in different areas of the spectrum, this could be true.

    David Kachel mentions this in his articles and I have observed an increase in contrast of Tri-X when using a #25 filter, meaning that the strongly red light source seems to render more contrast than "neutral," unfiltered light.

    This could be caused by sensitizing dyes, differences in emulsion layers etc. Modern films are very complex and there are many possible causes to look into. Since unmanipulated silver halide crystals are not usually sensitive to green and red light, the things done to make them so would likely be the place to look, however, not in the nature of the silver halides themselves.

    Best,

    Doremus Scudder
    www.DoremusScudder.com

  5. #5
    David Lyga's Avatar
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    To clarify, I am not talking about haze, Michael R. The gray scale was only about 3 feet away. There really IS an increase in contrast and it is, I believe, beneficial when it comes to printing. And Doremus is correct when he says that it is NOT in the nature of the silver itself: Just place a K2 filter in front of your eye and then quickly remove it (in shaded conditions). There really IS something about bluish light that lightly veils contrast. I have always noticed this even without taking the photographic process into account. I simply can see (and perceive) better with lower Kelvin temps. The tones just 'fit' better. I am neither scientist nor philosopher but the warm light is more accurate both in tonal values and in subjective perception. - David Lyga.

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    Sorry about that - I read your post but then mysteriously forgot about the part where you described the test you performed.

    A film's rendering of values is obviously influenced by its spectral sensitivity. But leaving film aside, I'm still puzzled as to why the human eye would see/perceive more contrast in a grey scale under lower temperature light at close distances.

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    Quote Originally Posted by Michael R 1974 View Post
    ...I'm still puzzled as to why the human eye would see/perceive more contrast in a grey scale under lower temperature light at close distances.
    If there's an answer, it's probably in Livingstone's book, Vision and Art: The Biology of Seeing. Highly recommended.
    Bruce Watson
    AchromaticArts.com

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    I'd think it has to do with spectral sensitivity of the film, which also ends up affecting the effective speed of the film. Shooting indoors under tungsten light can be thought of as equivalent to shooting through a yellowish filter (which your TTL meter might not compensate for properly). It increases contrast a little bit and reduces the amount of light reaching your film. For motion picture, Kodak gives daylight and tungsten ratings for its B&W film. For the most part, I think they tell you to rate it 1/3 of a stop slower indoors, e.g. 250 outdoors, 200 indoors.

  9. #9

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    David, the eye is more sensitive to yellow light than blue, that's why you can see much better at night with 2700-3200k headlamps on your car that 6500 or higher ones. The european countries had a reason for mandating yellow tinted bulbs decades ago.

    Not that this is relevant to film.

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    There are two different issues here that we should be careful not to conflate.

    First is the question of whether different colored light (be it filtered or "warmer" due to lower color temperature) has an effect on the contrast rendering of a particular film. If this effect exists (and I think it does), then it is a characteristic of the film, i.e., how it reacts to different colored light. I would speculate that there is different contrast rendering in the differently sensitized emulsion components that explains this.

    Second is the way the human eye works; what its spectral sensitivity is and how we perceive visually. Human eyes are most sensitive in the green/yellow area of the spectrum, as mentioned above. Another characteristic of the eye is that it cannot focus red and blue wavelengths at the same spot, which causes the "vibration" one "sees" when pure red and blue are juxtaposed, and why we may see more "sharply" when we filter out one or the other of the extremes (e.g., looking through a yellow or orange filter). This also explains the "sharpening" effect of yellow-tinted sunglasses.

    The film sensitivity/contrast issue is easy to test and then use in the field. David has made a good start by shooting his gray scale with a yellow filter. I test all my filters this way and find that different films react differently to different colors, and that the most extreme filters, i.e., the deep reds, blues and greens, are the ones with the most effect.

    If you are interested, I've detailed my views on metering through filters and my testing methods here a time or two. A quick search should turn them up.

    As I mentioned earlier, David Kachel talks about this in great detail. Check his article for more at http://www.davidkachel.com/historical/zsfilter.htm


    Best,

    Doremus Scudder

    www.DoremusScudder.com

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