Originally Posted by
Diane Miller
The patch tool, or Spot healing brush used on more than a spot, will preserve any noise, whereas a low opacity clone will smooth out noise.
A great way to see any cloning artifacts like this is to make a Curves layer above the stack and bring the contrast way up (LL point moved right and UR point moved left) then change the mode to Luminosity. Patch or redo the cloning in that view then toss the Curves layer. A similar approach works for cloning in very light or dark areas.