Thread: Is overexposing by 2 stops the same as using ISO200 on BMCC/BMPCC?

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  1. #1 Is overexposing by 2 stops the same as using ISO200 on BMCC/BMPCC? 
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    Hey peepz,

    tell me. Is it?
    I havent done testing on that.
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  2. #2  
    Senior Member DPStewart's Avatar
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    No.
    If anything it is the opposite.
    Also - it all only applies if you are shooting in ProRes as the RAW image is exposed the same no matter which ISO is used. The ISO data is just metadata in RAW and you can change the ISO later in post with perfect normal results.

    When shooting in ProRes you can UP the ISO setting to get a brighter exposure just like on any camera.
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  3. #3  
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    Quote Originally Posted by DPStewart View Post
    No.
    If anything it is the opposite.
    Also - it all only applies if you are shooting in ProRes as the RAW image is exposed the same no matter which ISO is used. The ISO data is just metadata in RAW and you can change the ISO later in post with perfect normal results.

    When shooting in ProRes you can UP the ISO setting to get a brighter exposure just like on any camera.
    mm why is it the opposite? If raw is only metadata but changing the ISO to 200 down from 800 gives a perceived darker image then shouldn't exposing correctly but for a 200 iso image mean you over expose by 2 stops?
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  4. #4  
    Senior Member DPStewart's Avatar
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    Quote Originally Posted by Ryanite View Post
    mm why is it the opposite? If raw is only metadata but changing the ISO to 200 down from 800 gives a perceived darker image then shouldn't exposing correctly but for a 200 iso image mean you over expose by 2 stops?
    This is a matter of wording.
    The original question was "is over exposing the same as..." - implying that you are over exposing the image as in ETTR, not "exposing FOR an image". If it was worded that way then it wouldn't be the opposite. Perhaps I was being the Grammar Nazi, but I have had folks ask it both ways.
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  5. #5  
    Senior Member LochnessDigital's Avatar
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    I think what Dane was trying to say was ISO settings are irrelevant in RAW. What matters is what you're doing at the sensor level.

    If you shoot 800 and then shoot 200 without doing anything else, the exposure to the sensor didn't change, so the images will be the same.

    But if you rate the sensor for 200, your light meter will tell you to expose 2 stops brighter images than if you had your meter set for 800, yes.
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  6. #6  
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    Quote Originally Posted by LochnessDigital View Post
    I think what Dane was trying to say was ISO settings are irrelevant in RAW. What matters is what you're doing at the sensor level.

    If you shoot 800 and then shoot 200 without doing anything else, the exposure to the sensor didn't change, so the images will be the same.

    But if you rate the sensor for 200, your light meter will tell you to expose 2 stops brighter images than if you had your meter set for 800, yes.
    Ah yeah, it is how you interpret the question haha.

    I'd have it set to 200 in raw then use false colours on a monitor to expose correctly to achieve exactly 2 stops over.
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  7. #7  
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    Sorry Dane, I am not a native speaker, so this was lost in translation I guess.
    So my workflow for very low key stuff atm is: Exposing an image like I want it to be @800ISO (in ProRes) at T5.6. Then when the shot is about to roll I open up to T2.8. (Of course I will check before that nothing clips that I dont want to be clipped.)
    Thanks guys, I will try 400 and 200 ISO for my next low key shoots.
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  8. #8  
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    Quote Originally Posted by Rotbart View Post
    Sorry Dane, I am not a native speaker, so this was lost in translation I guess.
    So my workflow for very low key stuff atm is: Exposing an image like I want it to be @800ISO (in ProRes) at T5.6. Then when the shot is about to roll I open up to T2.8. (Of course I will check before that nothing clips that I dont want to be clipped.)
    Thanks guys, I will try 400 and 200 ISO for my next low key shoots.
    Do you mean change the ISO instead of opening up the stop as a means to ETTR? That's not the same at all.

    Shooting Prores log at 200 ISO is ill advised unless you're certain you don't need that information down at the bottom. You're just going to crush the blacks 2 stops, it's much easier to push information down in post than it is to bring it up.

    If you're shooting raw there is a caveat for shooting at lower ISOs. It's been a while since I used the pocket so correct me if I'm wrong. Essentially the histogram represents sensor saturation and is always the same but the zebras are based off of the debayer so shooting at 200 ISO will never show clipping on 100% zebras. I believe you need to set zebras at 100% for 800, 90% for 400, and 80% for 200. Maybe 5% less just to be safe.

    Best really to draw your own conclusions. Just go out and shoot a fairly high dynamic range shot and without changing the physical exposure roll through the ISOs and see how it affects the signal distribution.

    Good Luck
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  9. #9  
    Senior Member Frank Glencairn's Avatar
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    Quote Originally Posted by Rotbart View Post
    Sorry Dane, I am not a native speaker, so this was lost in translation I guess.

    Thanks guys, I will try 400 and 200 ISO for my next low key shoots.
    Yeah, basically that's what I do for moody dark shots.
    I set the camera to 200, light till i'm happy, switch back to 800, and shoot.

    Have a look: https://frankglencairn.wordpress.com...ergiversation/
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  10. #10  
    Quote Originally Posted by Frank Glencairn View Post
    Yeah, basically that's what I do for moody dark shots.
    I set the camera to 200, light till i'm happy, switch back to 800, and shoot.

    Have a look: https://frankglencairn.wordpress.com...ergiversation/
    I'm a bit confused... You're talking about RAW ?

    TBH, I don't fully understand this hole idea of overexposing by 2 stops after you're happy with the lighting...

    EDIT : I took a look at the link provided and man, are those frames eyecandy. The cinematography award is well deserved.

    I think I got it : when you're overexposing by 2 stops, you basically want to have cleaner blacks when bringing down the exposure in post. Is that it ?
    Last edited by Stefan Antonescu; 04-30-2018 at 10:53 AM.
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