GaryG

Hi Tony,

You won't get diffraction spikes in a refractor - the effect in the image you posted looks to me more like pinced optics. By that i mean the cell that holds the lenses in place normally has grub screws to hold/align the lenses, when the cell gets cold it shrinks fractionally and pushes the grub screws into the lenses.

I have seen this on my 90mm refractor but only when it got to a sub zero temperature.

If you're very brave you could try loosening the screws by a very small fraction of a turn but i think a better option would be to use a dew heater which will lift the temp of the cell and lenses so hopefully remove the effect you are seeing & any dew!. That's my plan for my 90mm scope.

Gary