Thread: Color shift at different F stops

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  1. #1 Color shift at different F stops 
    Senior Member david evans's Avatar
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    Hey guys,

    I was trying out a new lens and noticed something really interesting. Not sure if it's the lens or the ND, but what I did was shoot at F8 and then F2 and the skintones look much more natural and interesting to me at F2 (pinkish and less yellowish than at F8). In order to get the same exposure I used a Heliopan gradual ND, but I wasn't expecting the end result to be so different.

    I don't think it's IR getting in there (because of the strong ND at F2), because I have the rawlite OLPF, which has a very good IR cut... and well, it just doesn't look IR to my eyes. IR would've messed up the entire image.

    Here are two DNGs that show exactly what I mean. Besides the sharper look of the F8 DNG, you'll notice a more yellowish skintone, compared to the more natural and pinkish color of the F2.

    Can you guys please download these two DNGs to see if I'm looking at this the right way? White balance is a little high compared to the "correct" color temperature.

    F8
    https://www.dropbox.com/s/jcxvges580...00000.dng?dl=0

    F2
    https://www.dropbox.com/s/czndb80h15...00000.dng?dl=0


    After some basic CC, I was able to get both skins to match:



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  2. #2  
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    Bottom corrected frame tint is pretty off from the top. Too much magenta.

    Most lenses have less contrast wide open, and almost all ND filters affect color and contrast to a significant degree. The difference is not surprising. A good DP knows equipment in and out, down to every filter, lens groupings, coatings etc and how they will affect the image and will choose accessories accordingly.

    Optics with the least amount of artifacts are prohibitively expensive, and are often rented.
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  3. #3  
    Senior Member david evans's Avatar
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    Quote Originally Posted by GeranSimpson View Post
    Bottom corrected frame tint is pretty off from the top. Too much magenta.

    Most lenses have less contrast wide open, and almost all ND filters affect color and contrast to a significant degree. The difference is not surprising. A good DP knows equipment in and out, down to every filter, lens groupings, coatings etc and how they will affect the image and will choose accessories accordingly.

    Optics with the least amount of artifacts are prohibitively expensive, and are often rented.
    Hey Geran,

    yeah, bottom has much more magenta which is (I imagine) why I like the skin tones so much. I'm much more of a magenta guy on skin tones (sorry about that, Fincher). But yeah, everything else seems a bit affected by it too. But it does look like a simple situation to solve in post.

    so in your opinion, the increase in magenta on the bottom image is ND related?

    EDIT:

    Of course, less contrast and a softer look is to be expected at low apertures. What I didn't expect was the increase in magenta, but still... Nothing to worry about and an easy fix in post.
    Last edited by david evans; 10-23-2019 at 02:36 PM.
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    The F/2 shot is also much later in the sunset. That will shift your hues considerably. You can tell by how her face is getting blasted by light compared to the F/8 shot, and how much longer her shadow is.

    With that new information it's hard to say how much of an effect each variable is having on the image, but yes, in general ND filters will change the color balance of lighting entering the lens. A more controlled test would answer the question.

    Blackmagic cameras all tend green to various degrees, so I would've added some pink back into her skin as well in the F/8 image.
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  5. #5  
    Senior Member david evans's Avatar
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    Quote Originally Posted by GeranSimpson View Post
    The F/2 shot is also much later in the sunset. That will shift your hues considerably. You can tell by how her face is getting blasted by light compared to the F/8 shot, and how much longer her shadow is.

    With that new information it's hard to say how much of an effect each variable is having on the image, but yes, in general ND filters will change the color balance of lighting entering the lens. A more controlled test would answer the question.

    Blackmagic cameras all tend green to various degrees, so I would've added some pink back into her skin as well in the F/8 image.
    Geran, just to clarify, both shots were taken exactly at the same time. It was literally just lower the aperture and rotate the ND.
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    Interesting. Well, if that's the case, then your filter is imparting a rather large amount of color shift on your image. I guess it's just hard to see the shadow of her head in the f/8 image.
    F/2
    f2.JPG
    F/8
    F8.JPG
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    David, I don't know which camera you use, in my experience the old pocket and micro have a strong magenta shift with large apertures.
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  8. #8  
    Senior Member david evans's Avatar
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    Quote Originally Posted by Max Minoia View Post
    David, I don't know which camera you use, in my experience the old pocket and micro have a strong magenta shift with large apertures.
    Hey Max. I'm using the Ursa Mini 4.6k and I've heard about problems with the first units about magenta cast and vignettes and slower fstops but never at fast apertures. I'm incline to the ND but will try the test again with a different ND. Thanks!
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  9. #9  
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    It’s the filter for sure.

    A variable ND which is what you used to get your different exposures works by using two polarising filters.

    As you polarise then more you get a heavier ND effect.

    But they are also notorious for colour casts.

    The sooner you get off then the better.

    Sure sometimes you really need the convenience of them but they suck on affect colour and resolution.

    JB

    Whoops just noticed you said gradual ND.

    Heliopan are also a popular variable ND. Did you mean variable or gradual.

    JB
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  10. #10  
    Senior Member david evans's Avatar
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    Quote Originally Posted by John Brawley View Post
    It’s the filter for sure.

    A variable ND which is what you used to get your different exposures works by using two polarising filters.

    As you polarise then more you get a heavier ND effect.

    But they are also notorious for colour casts.

    The sooner you get off then the better.

    Sure sometimes you really need the convenience of them but they suck on affect colour and resolution.

    JB

    Whoops just noticed you said gradual ND.

    Heliopan are also a popular variable ND. Did you mean variable or gradual.

    JB
    Hey John. Thanks for helping. It's a variable ND from Heliopan. After reading a lot of reviews, I ended up buying it because a lot of the reviews stated it had no color cast. I'll try to do a comparison to see at what point in the rotation the red shift becomes apparent.
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