This one is being trotted out with ever increasing frequency these days as manufacturers release new cameras with more pixels per square inch than ever before. Especially Nikon, who seem to have decided everyone needs to print at A3, with the D800 at 36Mpixel and even the new entry level Nikon DSLR the D3200 packing 24Mpixels.
I currently use a D700 most of the time which “only” has 12Mp spread across a 36mm sensor (“35mm” sensors and film are actually 36mm – go measure it if you don’t believe me ). It performs really well at high gain (the so called “ISO”). I was concerned about the performance of the D800 at high ISO ratings – if I switched, would I still be able to take pictures in relative darkness, handheld and so on?
Now, sure, if you took the same image at a high ISO rating with a D700 and a D800 and zoomed both to 100%, the D800 image would have more noise. But! You zoomed the D800 image more. A lot more. Zoom the D800 image to the *same* magnification as the D700 image at 100%, and what you’ll find is that the noise is the same. It makes sense – if you divide the same physical area of sensor into 3 times the pixels, but then squash the image down by a factor of 3, the extra noise is lost in the re-sizing. There will be some loss due to inefficiencies and the borders around the photo-sites sure, but on this comparison, the D800 shot looks better than the D700 (D3 on the test) to me (and about the same as the canon 5d MKIII):