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  1. #1

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    Portra 160 VC or color negative exposure experts?

    Hi from Barcelona, this is my first post here...

    My question is:

    How does exposure affect Portra 160 VC's tone if we talk just about color temperature?

    I'm testing it and found it goes both warm and cold with overexposure depending on the kind of light in the scene, and there's no optimal ISO rating: there are optimal ISO ratings depending on the kind of light... I find the best, cleanest, most accurate colors, are obtained after incident metering at 160, 80 and 40, depending on the nature and direction of light, and looks like the change in color temperature is more than visible with a 1 stop variation...

    Has someone got similar results?

    Cheers,

    Juan

  2. #2
    markbarendt's Avatar
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    Welcome,

    With negative film you are getting 3 separate exposures, R,G,B.

    Exposure choice just gets them all on the film at some brightness level, it doesn't change the film's temperature response.

    Color correction/balancing is an expectation/requirement of the process during printing.

    You can also use filters on your camera to change the color balance.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  3. #3

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    Thanks for the welcome, Mark...

    Indeed I used a B+W 81B filter on my Nikkor 105 2.5 for all the shots in the test, those under direct sun and of course those in the shadows... Have you used that filter? Its tone is a soft, warm delicate yellow, very mid afternoon sun-like, instead of the usual Nikon A2 I use for landscapes for an even warmer look: I prefer the B+W for skin (less amber...) My test was done by noon, so the direct light used was neutral, and not as warm as to consider my filtering excessive... I used that filter to replicate my real shooting...

    I did test two different scenes under direct frontal sun, two under lateral direct sun, and two in the shadows, and each pair showed exactly the same results... If you have a serious test where no tonal change regarding color temperature: cooler or warmer frames can be seen when comparing N, N+1 and N+2 (incident metering) I'd like to see it...

    Thanks a lot!

    Cheers,

    Juan

  4. #4

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    It is worth noting that if one of the color components starts to shoulder off (or behave in some other nonlinear manner) at a given amount of exposure, then the color balance would shift. I don't know how this applies to Portra 160VC.

    When I look at the Portra characteristic curves, I do see the green curve having a noticeably different slope than the others.

  5. #5

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    You can look at the Portra film curves here:

    http://www.kodak.com/global/en/profe.../e190/e190.pdf

    They are all linear if you stay off the toe, so colors should be consistent unless you under-expose.

  6. #6
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    I have to add that if you shoot in too warm or too cold light and want to correct it in printing - and you don't have filters with you when shooting - then overexpose a bit. This way you can stay off the toe for every curve. There is more linear reserve for overexposure. OTOH, if you shoot at correct color temperature, box speed gives you guaranteed results.

    You can overexpose as much as the filter factor for the appropriate filter would be, or maybe a little less. For example, if you overexpose two stops when shooting in 2800K tungsten light, you get the blue curve at the same place you would get with 80A filter (IIRC). Red curve gets overexposed severely without the filter, of course, but it can withstand it much better than two stop underexposure in blue curve.

  7. #7

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    Quote Originally Posted by Tim Gray View Post
    It is worth noting that if one of the color components starts to shoulder off (or behave in some other nonlinear manner) at a given amount of exposure, then the color balance would shift. I don't know how this applies to Portra 160VC.

    When I look at the Portra characteristic curves, I do see the green curve having a noticeably different slope than the others.
    Hi Tim,

    I agree with you... There is a shift in color balance... Certainly it must be based on slight higher under or overexposure in one layer...

    To be precise about my test:

    My scenes (warming filter on always: just one third of a stop so I metered at 160 always anyway...) under direct sun show underexposure at box speed (160 incident), and a cool (blue-magenta) shift giving sick, dark greens, and slightly unbalanced skins... If the sun is right behind me, +1 is great, with vibrant sunny mood (+2 clearly washed out), and if the sun is lateral, +1 is cold yet, and +2 is perfect: warm and with open shadows and saturated colors.

    But my scenes in the shadows are just the contrary: at box speed (160 incident and filter on) are warm and very nice, and +1 and +2 produce colder results! (+2 more than +1, but +1 clearly cold)... Identical on the two soft light scenes I did!

    This made me remember sometimes there are crossed opinions about exposure and overexposure of color negative film: while the common belief is overexposing a stop, some people say they prefer not doing it because the best colors are found at box speed: all my previous tests for years were done giving the highest importance to direct sun... But now with different light scenes to be sure and also twice to double check results, I can't forget what I see... Direct sun likes overexposure, but soft light doesn't... I can't imagine the technical reasons, but they're here... And I didn't scan home: I'm checking pro lab prints: they scanned after I told them not to correct anything while scanning, and knowing I was looking precisely for color variations produced by different exposure values...

    I'll shoot for some time like this... Of course AE can be very bad here, and even any in camera metering, as a one stop variation from incident is very noticeable... I have years experience in color balance and in selective color in photoshop, and I know that even if we can do things, once the scan is too cold, no matter what we do, it will never look warm and real sunny and happy even if we place the skins just where we want... That's why I'm being picky with this...

    Maybe someone shooting Portra 160 VC can use three frames in the middle of a roll to try this recipe and tell us later if those frames came out great...

    Direct sun, incident+1 with warm filter... Lateral sun, incident+2 with warm filter... Shadows or overcast, plain incident with warm filter...

    Yet I'm curious about the chemical / optical reasons for that "inverse" behavior depending on the kind of light...

    Could it be something about the scanner detecting a much colder image when the scene is a non-direct sun one? If it's that, what really matters is that the scanners work like this, and the direct scan prints are beautiful even before any digital treatment of color...

    Let's wait for some other members opinions and results...

    Cheers,

    Juan

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    Quote Originally Posted by Robert Budding View Post
    They are all linear if you stay off the toe, so colors should be consistent unless you under-expose.
    Agreed, they are linear, but I'm seeing different slopes for sure. I fitted to the plot and the blue curve is definitely steeper than the other too. I would think that means that at higher exposures, the blue layer is denser compared to the others than at lower exposures. But maybe I'm reading too much into the chart.

    Also, you linked to the older Portra sheet. The thing I'm talking about is more evident in e-4040.

    Also, Juan, did you have a gray card you are using as a color reference in your shots? I would think that is important for this kind of test...

  9. #9

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    Quote Originally Posted by Tim Gray View Post
    Agreed, they are linear, but I'm seeing different slopes for sure. I fitted to the plot and the blue curve is definitely steeper than the other too. I would think that means that at higher exposures, the blue layer is denser compared to the others than at lower exposures. But maybe I'm reading too much into the chart.

    Also, you linked to the older Portra sheet. The thing I'm talking about is more evident in e-4040.

    Also, Juan, did you have a gray card you are using as a color reference in your shots? I would think that is important for this kind of test...
    I didn't include a gray card this time both because I did it shooting unknown people in the street, and because I didn't want to print the gray card neutral (should always appear warm because of my filter, and there would be no way to decide exactly how warm...), so my goal was finding the point of exposure where a given scene looks just like I saw it, and not the usual colder renderings... And indeed I did include some grays and neutral tones (floor, buildings, etc...) and on them it's easy to see the color temperature variations... Every image was (quickly and handheld) done at N, N+1 and N+2, and I did two scenes for direct sun, two for lateral sun and two for shadows, and on each couple the results are gradual on those neutral tones, and identical... And yesterday I checked my Sekonic with all my cameras and everything is spot on...

    Another thing that surprised me, is that finally the best possible amount of light I found for every kind of light scene, curiously was EXACTLY the amount of light I use for B&W... For B&W I use N for soft light, and +1/+2 for direct sun (with shorter development) depending on the angle of light... I don't know if I should think this is strange or logical...

    The skins change, and the neutral tones change in an even more visible way, but the green tones (grass, trees, bushes) are the ones that suffer the most evident underexposure at box speed on direct sun... I'd say the green layer is the most sensitive to underexposure, or the one that requires more light or more precise exposure, or the one with less latitude... One stop before there's a bit of blue present in all greens (totally unreal grass tone), and one stop after the best value, the green and all the rest are weak and washed out (green goes to yellow...)

    I'd like to see someone else shooting with these metering values, and then comment... This is the first time in all my life that I feel I can get the best tone from a color negative scan without any trace of doubt... Just as if I was using slide film... Not just the skin, but the whole mood is "sunny" as we see the real world...

    Cheers,

    Juan

  10. #10
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    Quote Originally Posted by Juan Valdenebro View Post
    Thanks for the welcome, Mark...

    Indeed I used a B+W 81B filter on my Nikkor 105 2.5 for all the shots in the test, those under direct sun and of course those in the shadows... Have you used that filter? Its tone is a soft, warm delicate yellow, very mid afternoon sun-like, instead of the usual Nikon A2 I use for landscapes for an even warmer look: I prefer the B+W for skin (less amber...) My test was done by noon, so the direct light used was neutral, and not as warm as to consider my filtering excessive... I used that filter to replicate my real shooting...
    If I were shooting slides I'd probably use the filter like you suggest, because in that situation you are using the camera to expose the media that will become a finished product.

    With negative film things are different, the negative is only an intermediate step, it requires another exposure and color correction, no if's, and's, or but's.

    A very slight tweak to that color correction will replicate an 81B. (Instructions to a good lab will also get this result without the need for an 81B.)

    Quote Originally Posted by Juan Valdenebro View Post
    I did test two different scenes under direct frontal sun, two under lateral direct sun, and two in the shadows, and each pair showed exactly the same results... If you have a serious test where no tonal change regarding color temperature: cooler or warmer frames can be seen when comparing N, N+1 and N+2 (incident metering) I'd like to see it...

    Thanks a lot!

    Cheers,

    Juan
    There would be temperature changes if you had, for example, underexposed the blue layer in one shot then increased exposure.

    Robert Budding provided a link to the Kodak data on this film, on page 8 at the top corner notice the characteristic curve and that there's no shoulder shown in the graph, essentially they ran out of chart before the film ran out of straight line. The over-exposure latitude of C-41 film is huge.

    This is important because once you get all three colors exposed well (off the toe & onto the straight line portion of the curve) your color balance becomes stable. For normal contrast scenes you would have to over-expose 3+ stops before color casts might start again so exposing for the shadows essentially makes an easy to print negative.

    This is the reason many people overexpose C-41 a bit all the time.

    For large color temp changes an 80 or 85 filter would provide real value, for your example of slightly warming the scene I wouldn't bother; I'd just adjust at the enlarger because I'm already adjusting, there is no extra work.
    Mark Barendt, Beaverton, OR

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

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