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@tc88You are correct. In fact, DxO publishes normalized figures for this exact reason. The normalized ISO performance of the D800 is virtually identical to the D4 up to ISO 12,800.The D800 also has higher normalized color depth and dynamic range compared to the D4.
TTJ: great graphics! and very good point about printing on-site. One question: as to on-site events printing I would think you could consider a DX sensor such as the one on the D7000 or D5100 if you don't need high ISO. I have found they are adequate to at least ISO 800 and a refurbished D5100 body should be quite cheap.
You are correct. In fact, DxO publishes normalized figures for this exact reason. The normalized ISO performance of the D800 is virtually identical to the D4 up to ISO 12,800
TTJ: The D400, when it arrives, should be good for about one stop higher ISO than current DX sensors. But I also expect it will be 24mp. A D700 should work fine; if you can find one with a history you can trust. Any more manufacturer reconditioned D700 or D3 models appearing or one someone had and didn't use much?
The fact remains, when you downsample an image, the noise disappears. Comparing the D800 at 36mp to the D4 at 16mp isn't as fair as seeing what the 36 downsampled to 16 looks like; else, why don't we see how good the 16mp files looks upsampled to 36?
If you believe it is correct to take every sensor, and re-size them to 8mp and effectively remove 8-28mp of output of data? Then all you really need is to help Nikon with it's compact digi cam sales and skip the DSLRs.