Noise in clear blue skies can sometimes become an issue for landscape photography. Push and pull saturation just a little and noise becomes more apparent. Use a circular polarizer to darken blue skies, and noise may also come through more strongly. Avoiding under-exposure is key to keeping noise in blue skies to a minimum, as is keeping ISO as close to base value as possible.
The Nikon D700 has been to date the best camera I’ve owned for minimizing noise in blue skies. To see how the D7000 compares at its base ISO settings, I shot the next set of shots. You can click on each image’s thumbnail for a full resolution version, or you can click on the upper-left blue sky crops to see a swatch that has been normalized to the same equivalent resolution (at 12MP in this case) for an apples-to-apples comparison.
All shots were captured at identical or equivalent exposure settings and white balanced. Different lenses were used (35mm f1.8 for the D7000 vs. 50mm f1.4 for the D700), but in my experience, these lenses are fairly close in color rendering, and small differences can be offset through white balance adjustments.
D7000 @ ISO 200
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D7000 @ ISO 200, upper left crop
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D7000 @ ISO 100
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D7000 @ ISO 100, upper left crop
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D700 @ ISO200
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D700 @ ISO200, upper left crop
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Why should we worry about noise in blue skies? It turns out that if you perform Black and White conversions with a heavy emphasis on the red channel to get a dark rendering of a deep blue sky, noise can really come through, as these samples show.
D7000 @ ISO 200, B&W
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D7000 @ ISO 200, B&W, upper left crop
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D7000 @ ISO 100, B&W
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D7000 @ ISO , B&Wupper left crop
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D700 @ ISO200, B&W
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D700 @ ISO200, B&W, upper left crop
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Overall, it seems the D7000 at base ISO and at ISO 200 compares quite well with the D700 when it comes to minimizing blue sky noise. In the end, for color photos, as prints they do not exhibit noise as much as we can perceive on a computer screen. For B&W images, a little more care is required.