[avandonk]

Gary the faint reflection nebula intensity is barely above noise hence the fridge. In fact the vertical and horizontal banding of the sensor is what you are seeing. Without dithering it would be far worse. That image needs far more data and a larger dithering radius.

As you can well imagine a 300mm lens made of Magnesium Alloy will contract with temperature. The depth of field of the Canon 300mm lens is tiny about 2mm at 6M at f/2.8. I used to have to adjust the stepping motor that focuses the lens all night. Melbourne can start of at 20C in the evening and by morning it is down to 2C. This of course happens on lovely clear nights. Keeping the lens temperature constant is by far the best solution. I should have thought of it years ago.

The title was an attempt at wordplay.

Bert