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Old 01-09-2013, 08:01 AM
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Lee
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Is this bad seeing??

The last couple of nights have been frustrating.

Friday night I decided to image M74 and its supernova, the problem being it doesn't clear my roof until 11.30pm, and then at 20 deg alt. So a particularly low surface brightness galaxy, low in the murky light pollution, and the results aren't pretty! Guiding was all over the place too - I suspect a combination of poor seeing/low altitude and backlash in the Dec axis.... I had some pretty crazy graphs.

The first graph is guiding in the wee hours of Sat am.... I'm sure I was chasing the seeing, it did improve by adjusting up the min move to 0.5 (no image of this)....

The second graph is from about 20 hours later.... no guide output though, higher up on Dec 0. It shows I need some polar alignment adjustment with the overall dec drift, but the oscillations can only really be seeing - am I correct??

These graphs are a scale of 2.1 arcsec/pixel.

Last night I could only manage FWHM values of 4-4.5, when earlier in the week at the same location, 2.5-3.... hair pulling stuff!

The last two nights have been very warm compared to recent, and very dry.... from what I've read dewey nights are often better seeing? Maybe I should have stayed inside!
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Old 01-09-2013, 01:26 PM
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Shiraz (Ray)
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hi Lee. Seeing has been very variable here as well - last night started out at a bit under 3 and ended up over 5 arsec FWHM (ugly). Your graph looks like the sort of excursions I get in bad seeing. As far as I can tell, there is nothing much to do but put in the Ha filter or bin it 2x2 and get some low res colour on something that you might get good lum results on later. With your very low noise camera, you could also possibly try running some very short subs (eg 20 seconds) on something bright and see if that helps
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Old 01-09-2013, 03:44 PM
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h0ughy (David)
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i noticed antares was flickering so badly to the west last night that it was almost disappearing and the scintillation was extreme. but looking at the graph suggests to me something is also not right with the drift alignment on the mount as well?
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Old 01-09-2013, 04:31 PM
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Colour is over-rated

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Quote:
Originally Posted by Shiraz View Post
hi Lee. Seeing has been very variable here as well - last night started out at a bit under 3 and ended up over 5 arsec FWHM (ugly). Your graph looks like the sort of excursions I get in bad seeing. As far as I can tell, there is nothing much to do but put in the Ha filter or bin it 2x2 and get some low res colour on something that you might get good lum results on later. With your very low noise camera, you could also possibly try running some very short subs (eg 20 seconds) on something bright and see if that helps
I had some up to 5 too.... I think I packed up then!
The main problem was my PHD settings chasing it, then backlash catching up, so big correction, then rinse/repeat so it oscillated away....

My AF routine would normally report a HFR value of 1.5-1.8 or so at critical focus, last night more like 2.3-2.5 (10s exposures).


Quote:
Originally Posted by h0ughy View Post
i noticed antares was flickering so badly to the west last night that it was almost disappearing and the scintillation was extreme. but looking at the graph suggests to me something is also not right with the drift alignment on the mount as well?
Yes - I need to adjust azimuth.... previously I've been pretty happy just letting PHD guide it out, this amount has never caused field rotation over an hour or more... I'm planning to tighten it up.
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Old 03-09-2013, 06:56 AM
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Better seeing tonight.... it shows clearly in the PHD graph.... this is another graph with guide output disabled. Guiding itself was much better also, few hiccups, but certainly no multi-pixel deviations I've seen recently.

HFR values of images were improved by about 30% too....

Quite a dewey night... Does dew = better seeing in anyone's experience?
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Old 03-09-2013, 07:52 AM
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h0ughy (David)
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no dew doesn't mean better guiding - not in my experience but being dewy means the air was a lot calmer - now that would make a difference
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