Thermals or Atmospherics?

When you can just never seem to keep images sharply focused in your telescope, is it due to the atmosphere or that your scope has not yet acclimated to the outdoor temperature? To find out, shift the focus slightly inward. Just inside focus you can see turbulence in the upper atmosphere, usually a fast moving, horizontal flow. Now shift the focus still further inside. Way inside focus you can see the thermals in your scope; just to make sure, put your hand in front of the tube and watch the heat waves radiating from it. Also, atmospheric effects are often continuously variable - one minute the image is okay, then it looks as though you're viewing through a glass of water, then it's okay again, etc.