D4 vs 1Dx (Imaging Resource), RAW, ACR, 6400-12800

Started Sep 4, 2012 | Discussions thread
Lance B Forum Pro • Posts: 31,394
Re: D4 vs 1Dx (Imaging Resource), RAW, ACR, 6400-12800

bobn2 wrote:

2) The exposure is not the same for different cameras resulting in not valid comparisions of noise,

I have to disagree. If these two cameras were to shoot a similar scene, then the aperture, shutter speed and ISO would be what was actually used and therefore the result would be as shown.

The exposure is the combination of scene luminance, shutter speed and f-number only . If the scene luminance is the same (and I can't see any good reason why it should be different if the light positions and luminance remain the same) then the only way that the exposure can be the same is if the EV (combination of shutter speed and f-number) is the same. Here it clearly isn't, so the conclusion can only be that the lighting is different or the exposure is different or both. Whatever, the difference is enough to spread doubt on the validity of this test.

No not at all. Remember, not all cameras have identical ISO at a given ISO. So, the Canon may indicate ISO 6400 but actually be ISO 6700 and the Nikon may indicate ISO6400 but actually be ISO7000 or whatever. Therefore, to get a similar exposure for both, you would need to use slightly different aperture or shutter speed.

The actual exposure is important since it directly controls the amount of noise in the image.

It matters not whether they are off by a 1/3rd of a stop or whatever, it matters what was required to get the desired result just as you would if you used either camera in a particular scene in real life. The thing is, one may have slightly different ISO equivalent requiring slightly different shutter/aperture/ISO being required, but the point is, the end result would be the same.

You have a strange idea of how the cameras would be used in 'real life'. In real life in low light you have the constraints of smallest f-number and slowest shutter speed you can use. Those are absolute, and what matters is the result that a camera gives with those constraints. ISO is irrelevant. If you are wide open, and can give a maximum of 1/30 second, you use the ISO setting that gives you that, and it might be different on different cameras.

It's not a strange idea at all, when taken into context of what I said above. These cameras ISO's are not 100% accurate, so in real life on your Nikon D4 you may select ISO6400 but actually get ISO7000, so you would need to adjust one camera's shutter/aperture combo to equal correct exposure or to be the same as the other camera on test. So, my meaning of "real life" scenario is that to get equal exposure, then one will have different shutter/aperture combos, due to the slightly differing ISO, to get the same perceived exposure. This is generally only out by a small amount

The strange idea is that your exposure in low light is dictated by the ISO setting, not the slowest shutter speed and widest aperture you can use. There is no 'perceived exposure', all there is is the actual exposure, and that is what you want to be as large as possible to minimise noise. I'd guess what you mean by 'perceived exposure' is image brightness, which is set entirely by the tone mapping used in development.

No, the testing criteria is what dictates the ISO being used, you are reading things into it in order to boost your desire to find fault for some reason. The cameras were tested to ISO6400 and ISO12800 etc, so when they are set to these ISO's in order to test them to that ISO then an appropriate shutter/aperture to get a correct exposure. However, if camera A's ISO is supposed to be ISO6400, but is actually ISO5600 and camera B's ISO is supposed to be ISO6400 but is actually ISO7000, then when you set the aperture to say f8 and 1/125sec on each camera, then one will be more exposed than the other. Now, if you are testing both cameras at ISO6400 for testing purposes, like in the test that the OP, then to compensate, one camera will have to have a slightly different aperture/shutter combo to achieve the same exposure. I would assume that the testers would alter shutter speed rather than aperture in order to keep the same DOF.

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