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  #41  
Old 08-01-2014, 05:13 PM
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strongmanmike (Michael)
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I am thinking an easy way to check if your seeing is genuine sub arc sec or not might be to look visually through a small scope (6' or 8") at high power (or at a high powered image on a screen?) and see if you can detect any effect of the seeing ie is the image moving or blurring at all?... if you can then I would suggest it probably isn't sub arc sec seeing..?

Of course, this sort of situation is stuff of dreams (has anyone seen it?) and I suspect would only occur regularly at the very best locations on Earth, probably high isolated mountain peaks for example?

I do remember a fantastic night at Mt Campbell (780m ASL), just outside Canberra, back in 2006, I (and the CAS President) were using both the 6" Starfire and 12" SCT and the steady moments showed some perfectly still views in the 6" but they only lasted for a few seconds at a time (which makes a big difference) but while also pretty good, the image never quite settled perfectly in the 12". So, the resolution of a 6" is about 0.75" so I am guessing I was getting several seconds at a time of sub arc sec seeing...? To enjoy hours of this (like at La Palma and Chilean sites) would be simply breathtaking

Mike
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  #42  
Old 08-01-2014, 07:13 PM
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Peter Ward
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Of course you get (sort of) sub-arc second seeing....the question is...how long for? and over what aperture?

Paul, the resolution of your DS images is nothing unusual, hence I'd say you enjoy average seeing of about 2 arc sec (read: like the rest of the planet at sea level)

However seeing is not such simple a subject...

You are also probably getting small isoplanatic patches that regularly support sub arc second views....hence the great planetary images (interested readers can Google Babcock's work here).

However these patches can easily drift over larger scales during longer time periods, and also lose coherence at larger apertures.

Increasing the air density only makes this worse (ie sea level)

But to be blunt..I seriously doubt you get classically defined sub arc second seeing.

There is no co-incidence in the scientific community placing metre class optical telescopes at sites well *above* most of the atmosphere, and not at sea-level.

The seeing there is simply better.

Last edited by Peter Ward; 08-01-2014 at 08:42 PM.
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  #43  
Old 08-01-2014, 07:55 PM
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LewisM
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I get sub-arc hour at my location, occasionally, when I don't have 8/8ths stratus and embedded cumulo-nimbus. I am not at sea level either, I am proudly 12 metres above it, where it will make six-eighths of five tenths of nothing of a difference.

But, at my image scale and focal length, I can get pretty darned round stars. They might FORM a round star after pinpoint oscillating around for the 20 minute exposure, but hey, they are round!
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  #44  
Old 08-01-2014, 10:31 PM
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Here is my guiding. Average suburban back yard, EQ6, Lodestar and Orion ST80.
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  #45  
Old 08-01-2014, 10:49 PM
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RobF (Rob)
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Are those correction indicators on your tracking graph Bart? How do you get those to display?
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  #46  
Old 08-01-2014, 11:25 PM
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Click on the arrow on the bottom left hand corner of the graph window and hover over plot and select show corrections.
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  #47  
Old 08-01-2014, 11:58 PM
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Andy01 (Andy)
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Quote:
Originally Posted by Screwdriverone View Post
Looks Nice Paul,

I can only wish for results like that.

I feel like smashing this setup. Currently imaging Eta Carina. BUT, after drift aligning at least 3 times and getting a fairly flat PHD graph (even with pretty much SFA drift) I am getting some sort of SW drift in every second image????

Here is a pic of the garbage I am seeing now. Almost the entire night is a write off, I am not sure if it is balance or alignment or levelling or all three?

I seriously need to pull the finger out and install the pier and build the freaking obs, this portable garbage wastes soooooo much of my time and sanity and gives absolutely bull crap inconsistent results it makes me want to take to it with a baseball bat.

There. Rant over. Back to see if eggs are on the menu with my latest sub......

Cheers

Chris
Hey Chris,
Hope it's not a dumb question but why is you graph in Ra/Dec not Dx/Dy as recommended for the PHD graph/alignment procedure?
Cheers
Andy
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  #48  
Old 09-01-2014, 08:49 PM
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Screwdriverone (Chris)
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Hi Andy,

Ummm, I dunno (sorry, dumb answer ). It is always like that?

I don't use PHD for alignment procedure, apart from watching the drift when I turn off the guiding and adjust the Alt/Az screws on the HEQ5 using a meridian star and one in the east as low as I can go, etc.

I may take a look at this next time out and see what it does.

Chris
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  #49  
Old 10-01-2014, 12:08 AM
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Quote:
Originally Posted by Bart View Post
Here is my guiding. Average suburban back yard, EQ6, Lodestar and Orion ST80.
Much is masked at 400mm FL.... 1000mm would be better.... infact...2000mm would be a excellent benchmark to really establish seeing at any one location.
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  #50  
Old 10-01-2014, 01:12 AM
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I had a pretty steady night in Albany the night before last. here is my guide graph. OAG at 2.5m FL guiding at 1.2" / Pix.
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  #51  
Old 10-01-2014, 02:03 AM
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strongmanmike (Michael)
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Quote:
Originally Posted by Joshua Bunn View Post
I had a pretty steady night in Albany the night before last. here is my guide graph. OAG at 2.5m FL guiding at 1.2" / Pix.
Yeah, that looks pretty tight Josh, what equipment are you using?

Mike
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  #52  
Old 10-01-2014, 03:23 AM
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Thanks Mike, Using a PME, Planewave 12.5 CDK and internal guide chip on an STL11000.
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  #53  
Old 10-01-2014, 07:56 AM
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Quote:
Originally Posted by SkyViking View Post
Hi Paul, it is certainly an interesting debate. I have often wondered how the conditions rate at my site, but there is not much to compare with as these things are not discussed often.
Your guiding graph is very helpful in that regard. I have calculated the numbers for our respective guiding systems as follows:

Camera: ST-1
Pixel size (microns): 7.4
Binning: 2
Focal length (mm): 580
Resolution ("): 5.26
RMS (pixels): 0.106
RMS ("): 0.56

Camera: Lodestar
Pixel size (microns): 8.2
Binning: 2
Focal length (mm): 1273
Resolution ("): 2.65
RMS (pixels): 0.100
RMS ("): 0.27

I changed binning to 2x2 and as a result your RMS of 0.106 now corresponds to 0.5" (so twice as high as I thought, had it been 1x1).

I would think that if you do have sub-arcsecond seeing but your guider resolution is 5.26"/pixel then you might not be getting the full advantage of it? I don't know though since guiding works on a sub-pixel scale. But based on these numbers I'm actually thinking of going to 1x1 binning on my guider. I only bin to get higher sensitivity, but when the guide star is bright enough I'll try 1x1 instead - it's worth a try at least.

When speaking of seeing I consider this to be measured as FWHM over a certain period of time. That is what determines the final resolution of a deep sky image, which must be what we care about. For deep sky purposes FWHM must be measured with exposures equal to or greater than the guiding frequency. I'd say planetary imaging is different because exposures are a lot shorter and as a result of lucky imaging much finer detail can be picked up. I have taken planet images with the ToUCam that show much better resolution than the ~2" I get with longer deep sky exposures.

I'd be interested to know your FWHM's on typical deep sky exposures, are they sub 1"? If they are then you could comfortably be imaging at an image scale of say 0.3-0.5"/pixel (Nyqvist sampling) and take absolute killer images in terms of resolution.
I have used 1x1 at times in the past Rolf. If I had a good guide star it did seem to tighten up guiding results. No doubt that is from the higher resolution from the guide cam. That's a good reminder. If I get a good guide star I think I will use 1x1 next time as well to see if I get better results.

Greg.
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  #54  
Old 10-01-2014, 09:40 AM
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strongmanmike (Michael)
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Originally Posted by Joshua Bunn View Post
Thanks Mike, Using a PME, Planewave 12.5 CDK and internal guide chip on an STL11000.
Ah well, that explains it then

Mike
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  #55  
Old 10-01-2014, 10:21 AM
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Quote:
Originally Posted by Joshua Bunn View Post
I had a pretty steady night in Albany the night before last. here is my guide graph. OAG at 2.5m FL guiding at 1.2" / Pix.
Nice. Direct guide? or via the guide port?
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  #56  
Old 10-01-2014, 10:21 AM
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multiweb (Marc)
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I remember only a handful of nights in Oz with so called perfect seeing. Usually if it's real good you look up naked eye and you can tell straight away. No need to measure anything. It's quite obvious. Stars are just 'hanging' there. The view through a finder will be dead still. Again very obvious. Your guiding will flat line. As far as FWHM I get different readings using different programs so I don't know what to believe anymore but the best I got was around 1.5. The difference between 1.5 and 2 or 2.5 which is more the norm is quite dramatic. Realistically I get between 2 and 3 most nights, sometime 4-5 if the jetstream is out there. In the Pyrenees mountains in summer, over 1000m, on an good night the sky is very still. More than anywhere I've seen in Australia. The best I've seen would have been at 3000m in Winter. It's a bit like staring at a window in space. Nothing moves. But at -25c it would be a serious commitment.
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  #57  
Old 10-01-2014, 10:48 AM
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strongmanmike (Michael)
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In the Pyrenees mountains in summer, over 1000m, on an good night the sky is very still. More than anywhere I've seen in Australia. The best I've seen would have been at 3000m in Winter. It's a bit like staring at a window in space. Nothing moves. But at -25c it would be a serious commitment.
Ah Pic du Midi..? that was my dream location when I was a young budding astrophotographer in the 80's, the planetary images taken from there have been some of the highest resolution examples in the World, even before the digital age.

Mike
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  #58  
Old 10-01-2014, 01:12 PM
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multiweb (Marc)
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Ah Pic du Midi..? that was my dream location when I was a young budding astrophotographer in the 80's, the planetary images taken from there have been some of the highest resolution examples in the World, even before the digital age.
Yes it's a good location. Walked up there a couple of times. My avatar in my IIS profile was actually taken in the coffee shop on the top platform.
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  #59  
Old 10-01-2014, 01:31 PM
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strongmanmike (Michael)
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Yes it's a good location. Walked up there a couple of times. My avatar in my IIS profile was actually taken in the coffee shop on the top platform.
Walked..?? I thought you needed to take the cable car?
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  #60  
Old 10-01-2014, 03:43 PM
stevous67 (Steve M)
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Yes it's a good location. Walked up there a couple of times. My avatar in my IIS profile was actually taken in the coffee shop on the top platform.
Wow!

Steve
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