TUBE CURRENT
Tube currents are temporary aberrations that can sometimes be a great problem. Cooling down a telescope (to the outside temperature) before a viewing-session should not leave much room for this problem. Some telescopes (closed Catadioptrics, SCT/MCT) sometimes need a long cooldown or even don’t reach equilibrium due to a fast cooling from evening-temperature to night-temperature.

The above image shows a 1 wave tube-current at 1 wave intra-focus (left) and 1 wave extra-focus (right) and in-focus(middle). Notice that all images show the plume in the same direction. The direction is upwards in the telescope. The images were calculated for a 30% obstructed telescope since this type of current is common in such systems. The left-image shows a three-spiked effect that is only clearly seen on one side of focus.

Once more the left image is the perfect image (non-obstructed) the right has a 30% obstruction and 1 wave of tube-currents. The main effects are washing out of detail/color in upward-directions.