|
Some people are no doubt wondering why a temperature difference makes collimation difficult... when there's a warm layer in front of the mirror you'll get a plume of hot air rising and cold air around the outside falling, this will destroy the precise image needed to see diffration rings, and when they do momentarily appear they will be distorted by these air currents. If you watched them and believed what you were seeing to be true then you'd end up chasing your tail trying to get these rings to be centered. As the boundary layer gets better or worse then the amount of distortion changes. There's really nothing that can be done until all the boundary layer and other tube current related convection stops.
regards, Bird
|