Quote:
Originally Posted by multiweb
I reckon it was due to the primary temperature not being uniform. You might have had a hot or cold spot under the fans maybe. I had similar issues by applying gentle heat to a newt primary. Unless it's evenly spreadout you get those temperature differentials that causes stress in the glass and it translates to wonky star shapes.
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Definitely possible in some cases, but unlikely in mine.
I opened up the observatory, pointed the scope towards the sky and left it for an hour or so to cool down... never turned the fan on. Fiddled around for a bit, ran auto focus got a HFR of about 1.3px. Turned the fan on and ran AF again and got a HFR of over 2px. Then I noticed the elongation. Turned the fan off again, ran AF, HFR of 1.18px, no elongation... proceeded to image for hours with no on-axis elongation (off-axis is another story, as I mentioned above)
The fan was on for all of a minute or two, I don't think it was on long enough to deform the mirror and when I turned the fan off, I don't think it was off long enough for it to have recovered from that if that had been the case.