Sensor Noise

• As more pixels are placed on a sensor, their size gets smaller and the amount of random noise they generate increases. Since the D80 has a 10-megapixel sensor while the D70 has a 6-megapixel sensor, the random noise generated by the D80 sensor is louder.
  
  

Dark Noise

• When the shutter on the camera is open for longer than 1/60 of a second, additional modes of noise come into effect. Surprisingly, the D80 generates much more dark noise than the D70.
  
  

Moire

• Moire is a digital artifact created by an interaction of the pattern of the pixel sites and patterns on the object being photographed. Testing indicates that Nikon does a better job of compensating for them in the D80 than in the D70.
  
  

JPEG Conversion Artifacts

• When using higher compression rates to store the photo as a JPEG image, artifacts such as box structures can be created. As each new iteration of the camera is developed, Nikon does a better job of controlling JPEG conversion artifacts.
  
  

"Stuck Pixel" Noise

• The "stuck pixel" noise occurs when a pixel is always on. This is more noticeable when taking long exposures. The D70 and D80 compensate for this problem equally well.