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#1 Lacaille

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Posted 24 October 2020 - 12:05 AM

..on planetary imaging, you may have heard of the central importance of good seeing for producing the best images.   I thought I would post a sequence of images here that emphasise how seeing can change during a night, and that periods of good seeing may be fleeting.  You may think that someone like Kokatha Man, posting superb images here, is lucky to have good seeing, where he works in South Australia.  However,  he spends many hours imaging, travels widely with his scope to find areas of clear skies, and the results that we see here are the outcome of many, many hours of work, waiting for the elusive periods of good seeing.  (As the saying goes, the more he practises, the luckier he gets!).

 

There are apparently regions of the world where the seeing tends to be generally good - where I am in Canberra is not one of them!  The images below were taken during a session with Mars on the night of 20th October.  There was not a cloud in the sky throughout, but the seeing varied quite dramatically during the session.   I had been hoping to collect a nice sequence for an animation of 2 h, but as you will see, it was not to be.

 

I was using a C14, ADC, Barlow 1.5X, and ZWO290MM with RGB filters. I present only the R images to show how the seeing varied.  Note that I do not present these as evidence of superb seeing at any point - the best seeing I had was just OK.

 

First you have a period from 1056 - 1113 (UTC) of mediocre seeing.

 

Then at 1121 things go rapidly downhill to very poor (1130).

 

Things suddenly get briefly better around 1155, then go pear-shaped again for another half hour (1218-1230), until, just as I was about to give up for the night  (not in disgust, for I have become a philosopher as a result of nights like this, and accept the gifts of the Seeing Gods with stoicism), things suddenly got better and I rattled off the last four RGB triplets. At this stage, I should probably have stayed up, but I could barely keep awake.

 

Seeing changes 2020.jpg

 

I think the lesson is that, like anything else, you have to be out there practising.  You have to put in the hours.   Depending on your region, you may need to wait longer than others for the brief periods of good seeing.  Seasons may vary, and years - we seem to be having a bad year in south Canberra this year.  Seeing can also differ over fairly short distances - here in Canberra it can vary between the northern and southern halves of the city.

 

Regards

 

Mark


Edited by Lacaille, 24 October 2020 - 02:33 AM.

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#2 Tom Glenn

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Posted 24 October 2020 - 12:17 AM

Nice post Mark.  How many times have we seen posts in which a relative newcomer essentially says "I can't possibly have this poor seeing all the time, can I?", or "I should be taking better images than this", when the reality is they haven't put in even a fraction of the time necessary to get good results, or even make an assessment of the seeing quality.  Then, there is also the simple truth that most experienced imagers only bother posting their good results (for 100% understandable reasons.....who wants to post garbage!).  This leads some to believe that these individuals always enjoy success, which is simply not true.  And finally, there are a handful of lucky individuals, who truly do live in locations where the seeing is very good for much of the year, but these situations are not representative of the average either.  The net result is that beginning imagers will make incorrect conclusions from what they see here, and will often come away thinking there is some "processing magic" that they must be missing.  


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#3 Foc

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Posted 24 October 2020 - 01:21 AM

Nice collection.  Good or bad seeing the terms we all use on CN are usually subjective judgments and our expectations and standards can change from year to year or month to month as well as from place to place. I certainly have similar seeing where I live and from my experience this year might have thought 1130 as being not that bad seeing until shown otherwise by your images on either side of the seeing spectrum.  I guess the upside is that even if seeing seems bad each night if you keep out there long enough doing the captures you have a decent chance of a post worthy capture as well perhaps of a grumpy partner!


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#4 Tulloch

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Posted 24 October 2020 - 02:08 AM

That's really interesting, quantitative evidence of qualitative observations. It would be really interesting to line these up with minute-by-minute weather data, such as atmospheric pressure, wind speed, turbulence, jetstream, who knows?

 

I wonder if the BOM keeps data like this?

 

Andrew


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#5 KiwiRay

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Posted 24 October 2020 - 02:14 AM

This is really instructive, Mark - thanks for posting.  When I started imaging in 2015, I would go out for a few minutes, take some 40 s videos, stack a few hundred frames, and then wonder whether I could ever get anything better than the resulting (at best) below average-looking images. Practice, persistence, patience, and a bit of good luck are the recipe for acquiring images that you'd feel satisfied in sharing with others.  You were out for two hours, and still didn't catch any very good seeing - I'm not sure everyone appreciates the amount of work that goes into imaging and processing before we even have something good to share.


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#6 Lacaille

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Posted 24 October 2020 - 02:43 AM

Thanks for the likes and kind comments.  

 

That's really interesting, quantitative evidence of qualitative observations. It would be really interesting to line these up with minute-by-minute weather data, such as atmospheric pressure, wind speed, turbulence, jetstream, who knows?

 

I wonder if the BOM keeps data like this?

 

Andrew

Not sure Andrew.  One thing that occurred to me after posting, though, is that there is the additional factor of local temperature. I had cooled the scope to within one degree of ambient at the start of my session, but if the temperature started to plummet midway through the session I expect I would have got tube currents causing the appearance of bad seeing.  So there is another factor to consider.  I do recall that better temperature management, on the advice of Darryl back in 2017, was one of my breakthrough steps.  I haven't yet taken Darryl's advice to fit a thermocouple probe permanently into the scope for continuous measurement, but I will need to do that.

 

This is really instructive, Mark - thanks for posting.  When I started imaging in 2015, I would go out for a few minutes, take some 40 s videos, stack a few hundred frames, and then wonder whether I could ever get anything better than the resulting (at best) below average-looking images. Practice, persistence, patience, and a bit of good luck are the recipe for acquiring images that you'd feel satisfied in sharing with others.  You were out for two hours, and still didn't catch any very good seeing - I'm not sure everyone appreciates the amount of work that goes into imaging and processing before we even have something good to share.

Ah yes, I remember my days of running off a single short video and waiitng for something good to happen!  As Tom says, I was always looking for the "processing magic" unicorn to intervene!

 

By the by, some of us have requested that the pinned posts at the top of the Forum be updated to give folk starting out more up to date resources. It would be nice if that were done as everything gets turned over in the big reorganisation.

 

Regards

 

Mark


Edited by Lacaille, 24 October 2020 - 02:44 AM.

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#7 Vega700

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Posted 24 October 2020 - 02:55 AM

Interesting Mark. For me I take note of weather patterns when the seeing is good and installed my own weather station at home, and periodically check when the similar weather patterns occur. Then I don't waste time and after several years I have a pretty good idea when the good seeing will occur. For over here in the west the best time seems to occur once or twice a week.


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#8 Kokatha man

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Posted 24 October 2020 - 03:31 AM

An excellent example of how seeing fluctuates & that despite everything, it is doing those long grinds after you decide to set up & image that brings more opportunities Mark...of course, there are times when you realise it isn't worth hanging around...but the number of times when it looks mediocre & then sometime during the night there's a little or even longer window of opportunity...on October 9th it was a 300 second single r-g-b sequence right at the end that this occurred - & of course it can regularly not happen at all! :(

 

Re-collimating after the seeing turns to the better is not uncommon for us also btw... ;)


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#9 RedLionNJ

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Posted 24 October 2020 - 11:31 AM

Well-said and nicely demonstrated, Mark.  I'm sure you have a ton of worse images you could have displayed, too!



#10 Lacaille

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Posted 24 October 2020 - 07:09 PM

Well-said and nicely demonstrated, Mark. I'm sure you have a ton of worse images you could have displayed, too!


What makes you think that?

Seriously, though, I have some stuff that hardly looks like it was taken by the same bloke with the same gear, largely because of poor seeing (but at times due to technical errors e.g. overpowered Barlow for the pixel size and conditions).

#11 Lacaille

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Posted 24 October 2020 - 07:27 PM

Re-collimating after the seeing turns to the better is not uncommon for us also btw... ;)


Crikey! You guys! Going to have to lift my game!

#12 Astroroo

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Posted 25 October 2020 - 12:47 AM

Great combo Mark.

 

Last week I was imaging Mars religiously every night from Sunday to Thursday and best conditions were indeed on Tuesday (20 Oct).  I've made over 60 RGB runs starting at 10 and finishing at 2 - raw stack below is from 12:58 UTC (so shortly before our midnight).  Seeing stayed consistently good for the next hour and a half.. which is unusual for Canberra of late.  I was stacking as I was recording and moving cropped clips to external drive for archiving.

 

Yet to start WinJUPOS treatment, think about putting together animation once post processing is all done.  Agree that one needs a lot of patience and self discipline in this art, glad I've collected all this data while the planet was over 20".  The rig is now indoors waiting for clear weather again.

 

Regards,

Seb

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#13 kevinbreen

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Posted 25 October 2020 - 05:30 PM

If you are just starting out.... stop!!
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#14 dcaponeii

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Posted 25 October 2020 - 05:55 PM

If you are just starting out.... stop!!

Oh ye of little faith!!


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