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February 10th, 2010, 11:06 AM | #1 |
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ISO vs noise levels
Having just acquired a 5D Mkii, I was looking for info on the merits of manually setting the ISO vs Automatic when I came upon this ISO vs Noise Level graph.
Canon 5D Mark II Noise Levels vs. ISO - Canon Photography Group It would seem that the 5D respond best when set to it's "naive" ISO settings (100, 160, 320, 640, 1250) than to intermediary settings which it apparently must extrapolate. Strangely enough, according to the graph, the 5D Mkii shows less noise at ISO 1250 than at ISO 125, after which things get exponentially nosier from ISO 1600 onwards. In the mean time my question remains unanswered: when shooting video, what is the merit of setting the ISO manually vs the automatic settings. Ironically, this digital camera is forcing us to think "celluloid" all over again. cheers to all
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February 10th, 2010, 02:28 PM | #2 |
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Well, issues of noise aside, the primary advantage to setting ISO manually vs. auto is that it prevents the camera from changing exposure mid shot.
In terms of noise, yes you can minimize the noise by using the native ISOs, so that's one reason to do it. Another reason is that on auto the camera will often use a higher ISO than necessary in dark shots - it's trying to make the whole scene brighter when you might be fine with the overall look being dark. Setting it manually lets you decide what portion of the image is most important in terms of exposure. None of this, other than the native ISO noise issue, is any different than any other pro video camera. Auto anything is generally to be avoided if you care about getting the best possible shot and maintaining shot-to-shot consistency.
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February 10th, 2010, 07:56 PM | #3 |
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Hey Kalunga thanks for the link. Those are some interesting results. From that test it looks like it's a good idea to keep your camera set at ISO 640. By the way I think you are mistaken about "native" ISOs (the most popular ones are 50, 100, 200, 400, 800, 1600, 3200). And yes, stay away from Auto mode.
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February 10th, 2010, 11:02 PM | #4 |
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February 10th, 2010, 11:04 PM | #5 | ||
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There are just so many things wrong with the "testing" for the graph to have any useful information. I don't even know where to start. For one, analyzing test frames with the lens cap on is fine if you know how to correlate that with actual performance. Clearly the tester who made that graph does not. Furthermore, the bend in the curve occurs at exactly the arbitrary tonal level selected by the tester. Other levels would have bent the curve in other places, which obviously removes all meaning from the graph. Even for a still photographer, it has no correlation to anything useful whatsoever, but that goes several times over for video use.
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In any case, fixed exposure/brightness only applies to raw photographers. For video use, exposure has to float with ISO to retain fixed brightness, and in that regime, ISO 1250 has far more noise than ISO 125. Anyone with a camera knows that already. |
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February 11th, 2010, 12:50 AM | #6 |
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February 11th, 2010, 01:24 AM | #7 |
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February 11th, 2010, 01:32 AM | #8 |
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Thanks Daniel for the insight.
So much for "point and shoot" :)
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February 11th, 2010, 04:15 PM | #9 |
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February 11th, 2010, 04:38 PM | #10 |
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I touched on some of the reasons in post #5 above. The test conditions are with the lens cap on, raw stills, converted in ACR, with arbitrary settings. This results in a chart of completely arbitrary results. If he had measured the raw data directly, instead of with ACR, and correlated the bias frame measurements with the conversion gain for each ISO setting, the he could have created a chart with useful information. There's really no useful information in this chart at all for video shooters, though it's misleading for still photographers as well.
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February 12th, 2010, 10:19 AM | #11 | |
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February 12th, 2010, 05:06 PM | #12 |
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Here are my purely personal non scientific observations, after using the 5DmkII for a bit more than a year.
Stills and video look best at ASA 100. Stills and video start to show grain/noise at ASA 400. Stills and video are acceptable up to and including ASA 1600. So the way I use the camera is always shoot at 100 if you can. It is fine to go to 400, 800 and 1600 though it will add some grain/noise. Only if you really have to go higher than 1600. Like I said this is from looking at and working with video and stills professionally for about a year. And it is only my personal esthetic opinion, and it is how I use the camera. In low light I try to use a fast lens f1.4 prime or f2.8 zoom, rather than up the iso past 1600. |
February 12th, 2010, 06:04 PM | #13 | |
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February 12th, 2010, 06:28 PM | #14 |
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That's true, but the trade off is 1/3 stop clipped highlights. For example, when you set the camera to ISO 160, what it actually does behind the scenes is use ISO 200 (metered for 160), then reduce brightness by 1/3 stop. If the picture profile settings are set for enough contrast that the 1/3 stop isn't used anyway, then the loss of highlights wont be noticed. It's the exact same thing as ISO 50, except ISO 50 clips a full stop of highlights (and reduces noise by a full stop).
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February 12th, 2010, 06:37 PM | #15 |
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Yeah but I'm shooting full manual and don't rely on any in camera meter so whatever it does behind the scene doesn't matter as long as I get less noise in my video.
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