[The_bluester (Paul)]

Just a thought with the ED72 based on something I recently observed. I have not had a chance to re test yet. I was getting some odd bloating with mine (With an OSC camera) on bright stars, most noticeably the redder end of the spectrum.

While it was still in summer, I had one night that cooled rapidly and had really heavy dew and the scope dewed up really badly afte I went to bed (I had not got a heater on it at the time, who would think you would need it with a string of 30 degree days?) and it appears that it managed to wick moisture in between the objective elements (Air spaced)

It might well be why I was seeing what looked like tilt in some of the corners as there was a nearly complete ring of liquid water between the elements around the edge so parts of the lens were air spaced as they should be and parts had liquid separating them. I used it last week and even with a heater it dewed up and I realised that there was condensation AND liquid in between the elements.

I figured I knew what Skywatcher's response to it would be warranty wise with obvious water between the objective elements so I took a breath and disassembled the objective to dry and clean it yesterday. I might go again, I can see a tiny bit of haze still there after cleaning with cotton balls and isopropyl alcohol (Even the Bintel magic juice was leaving a residue)

If I go again I will go cotton balls and isopropyl then a rinse off with plenty of distilled water and let them air dry, but it is pretty good so I might not bother. Any marks are really obvious when you have the lens cell out as each lens is in focus when viewed from the other side so any smudges or stray wisps of cotton ball are really visible. If flats deal with it I will leave it alone. if anyone is thinking it, it is hard to see the two elements being indexed together, there is an O ring under the locking ring and the first half a turn or so as you loosen it (And again when tightening it) rotate the first element under the tension of the O ring so indexing the two would be a tricky affair, there were no obvious index marks either.

Hopefully I see some clear sky to test it properly soon, with more heat to ensure it does not do it again!