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The new Nikon D7000 is out, and a lot of previews has touted the "native iso" of D7000 to be 100.

What does this actually mean? I'm assuming it means it performs at its best at iso 100, which means if you're ok to sacrifice light sensitivity, you'll get really great images...?

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See also photo.stackexchange.com/questions/9263/… –  mattdm Mar 28 '11 at 0:04
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up vote 13 down vote accepted

As I understand it the "native" or "base" ISO is the sensitivity you get without amplifying the analogue signal you get from the sensor. It becomes important when the native ISO is higher than the lowest available on a camera (e.g. the base ISO is 140 and the lowest setting is 100). In this case the camera is likely to overexpose the image (as you can't unamplify the signal to recover the highlights) and the non-amplified signal is more likely to be affected by the read noise of the electronics (then read noise of the electronics is roughly constant so if you have a small signal the read noise is higher by comparison).

As already stated it's unlikely to actually be noticeable in images however if you always strive to use the lowest ISO the camera offers whenever possible, you may be wasting your efforts as the image quality may be just as high/slightly better one setting up.

For further reading:

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From what I gather, it appears to be yet another silly measurement for gear-heads to obsess over.

Here is a pretty good overview that I found regarding both Native Iso and Base Iso.

Obviously from the tone of my answer, I'm not really keen on such qualitative measurements. I suppose if you need a way to stack-rank compare bodies it might be valuable, but in my opinion it needlessly complicates things with criteria that aren't really that important.

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I saw that posting too, seems as reasonable an explanation as any. Anyways, I tend to agree with you, it's generally not really meaningful in actual practice, it's something for measurebators to argue over. –  John Cavan Sep 16 '10 at 21:45
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I have to agree. The more I learn about photography gear, the more I realize how little all the micro-measurements matter. Distortion, slight vignetting, base/native ISO, etc. are all pretty meaningless in the real world. Those that do have a visible effect can usually be corrected in post-processing these days, often automatically with the advent of lens profiles for various software. They may matter for scientific purposes, but its unlikely any scientific project would use any commercial grade equipment. –  jrista Sep 17 '10 at 16:15
    
Knowing what the native ISO of your camera is only marginally useful, yes, but knowing what determines native ISO is important to understanding how sensors work, which is worthwhile IMO –  Matt Grum Apr 30 '11 at 20:24
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ISO is changed by applying gain at the analog stage of the signal (which, incidentally, is why you can't change the ISO in raw), and the base ISO is the amount of gain at which the signal-to-noise ratio is the maximum.

In practice, the one at which the image is the cleanest. But that part is already obvious to everyone.

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