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Old 30-06-2019, 07:35 PM
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codemonkey (Lee)
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I fixed it!

So excited. Finally, after so long. My elongated, blurry stars were caused by... drum roll... my primary mirror fan.

I swear I tested that on an out of focus star at the very beginning of all these issues. Maybe the star was too out of focus?

Tried it again tonight on an in-focus field at the change was immediately apparent.

So now I'm capturing some more data on NGC 5128 and it's looking much better than before. Unfortunately it's getting a bit late in the season for NGC 5128 now and we only have a couple of partially clear nights scheduled this week...
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Old 30-06-2019, 08:38 PM
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Slawomir (Suavi)
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Fantastic news Lee, really happy for you and well done on your perseverance
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Old 30-06-2019, 08:47 PM
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Atmos (Colin)
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I know this has been the name of your existence for quite some time Lee so I’m glad it’s finally fixed
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Old 01-07-2019, 07:06 PM
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Thanks guys! Yeah, this has significantly impacted the quality of data lately, and has caused me to not image numerous nights so it's a relief to finally isolate the primary cause.

After turning the fan off last night I saw some of the sharpest subs I've ever seen, with FWHM of L down to high 1.5" Of course transparency was rubbish and I got fogged out, but that's not a surprise here at this time of year.
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Old 01-07-2019, 10:03 PM
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So is something loose allowing vibration transmission or is the fan faulty and excessively vibrating?
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Old 03-07-2019, 12:30 PM
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codemonkey (Lee)
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Quote:
Originally Posted by ChrisV View Post
So is something loose allowing vibration transmission or is the fan faulty and excessively vibrating?
Not sure yet, just established that turning the fan off improves FWHM significantly and fixes my on-axis elongation. Solution right now is: I turned the fan off.

Unfortunately it looks like this isn't the end of my woes (can't be, right? That'd be too easy!)... my recent issues had been across the whole field, so I was looking on axis when the subs came in. Now that I've had a closer look, I appear to have issues off-axis... think it's tilt at the moment but not sure.
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Old 03-07-2019, 04:24 PM
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Quote:
Originally Posted by codemonkey View Post
Not sure yet, just established that turning the fan off improves FWHM significantly and fixes my on-axis elongation. Solution right now is: I turned the fan off.
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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Old 03-07-2019, 04:33 PM
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codemonkey (Lee)
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Originally Posted by multiweb View Post
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.
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.
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