Jack,
Have been looking at the images of your neon lines again and something is puzzling me. They are obviously taken with the same camera but why are they different in that in one image there are three bright lines (plus fainter lines) but in second image only two are visible. Also I’ve noticed along with the doubling effect on the right hand line the fainter line next to it to the right again is still a single line,if doubling effect was caused by the collimating lens being pulled to one side then this line too would be distorted.
Regards
Alun