Re: Imaging in the Wind


Robert Chozick
 


Picture of wind shelter 
Robert 


On Jul 22, 2021, at 5:45 PM, Robert Chozick via groups.io <rchozick@...> wrote:

The temporary conduit solution works very well and is anchored with stakes and ropes. We use this at the Okie Tex star party and get gusts close to 60 miles an hour all the time setting up for a weeks time. You can set up the conduit and tarp shelter in less than an hour and it’s stores in a small area. I will find some pictures and send them. 

Robert 


On Jul 22, 2021, at 3:40 PM, W Hilmo <y.groups@...> wrote:



I think so, too.

 

The problem is that my wife would prefer if I not sink fence posts into concrete for a temporary solution.  My fear is that without a really solid anchor, our wind would simply blow it away.  We’ve been seeing 30ish mph for the last couple of weeks, but it can get significantly higher than that with little warning.

 

Also, if the fence were upwind, which is would need to be to function, any wind strong enough to move it, would blow it right into the scope.

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Robert Chozick via groups.io
Sent: Thursday, July 22, 2021 11:25 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Imaging in the Wind

 

A simple fence enclosure model would help greatly. 

Robert 

 



On Jul 22, 2021, at 1:04 PM, W Hilmo <y.groups@...> wrote:



I just wanted to follow up and say that using the motorhome as a wind block made a huge difference.

 

Based on the below results with the 175 refractor, I assume at this point that the mount itself is probably not the issue.  I have the rig set up on ground that is quite solid, and am using the 10” diameter portable field pier.  The pier height is 32” from the ground.

 

I’m wondering if the issue is that I leave the mount set up on the pier all the time.  In the last couple of weeks, our temperature has varied between 45F and 115F.  I suspect that the thermal cycling may affect the turn buckles.  It seems like they could be tighter than they are (although I find that if I tighten too much, it bends the hooks at the end of the turn buckles so that they open up).  I don’t adjust them often because I have a really good APPM model, and would need to recreate it each time.

 

I have plans for an observatory with a proper pier with a deep underground footing, but that won’t be until sometime next year at the earliest.  I’m going to need to find a temporary solution for between now and then. 

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of W Hilmo
Sent: Tuesday, July 20, 2021 4:44 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Imaging in the Wind

 

Interesting.  If I can get tracking like you are seeing, that would be great.  If I unplug the encoders, I’ll either need to set up guiding or program a PEM curve.

 

Out of curiosity, what you are using for a pier?  I am using the portable field pier, and if the whole thing is shaking, perhaps I could tighten the turnbuckles a bit.


Oh, and one other thing that may be interesting, or may be nothing, I never get tight stars that are elongated.  I either get tight, round stars, or I get big elongated blobs.  I also get satellite lots and lots of satellite trails, and they are generally straight lines.  I was thinking that these satellites just happened to coincide with some strong gusts.

 

-Wade

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Roland Christen via groups.io
Sent: Tuesday, July 20, 2021 4:32 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Imaging in the Wind

 

You can unplug the encoders and see what you get.

 

I got 30mph wind gusts here last couple of days with my 175 refractor on a 1600 encoder mount. Got round stars. Was watching the autoguider graph and saw only 1 arc sec or so deviations during a gust.

 

Rolando

-----Original Message-----
From: W Hilmo <y.groups@...>
To: main@ap-gto.groups.io
Sent: Tue, Jul 20, 2021 1:25 pm
Subject: [ap-gto] Imaging in the Wind

I've been doing a bunch of experimenting to transition from guided imaging with an SCT, to unguided imaging with a first class refractor.  Coincident to this, I'm imaging in a particularly windy area, which I moved to a few months before I received my AP130GTX.  Previously, I lived in an area with lots of overcast, but little wind.  It was also sheltered by being completely surrounded by forest.  My current location is wide open and completely unsheltered from the wind.

As mentioned, the scope is an AP130GTX.  The mount is an AP1600 with Absolute Encoders.  I'm finding that on calm nights (which are rare this time of year), I get nice, round stars at 10 minutes unguided.  With our typical winds, which are around 30mph over night, I get blobby and elongated stars.  Last night was windy, so the subs were all soft, with poor eccentricity.  I'm trying to determine how much of my soft stars are the the result of turbulence higher up, versus the mount and scope getting buffeted by the wind.

When I was blinking through the subs, I found the image that I've attached below.  It's interesting because there are crossing satellite trails at very different angles, that show signs of significant vibration.  I am guessing that what is happening here, is that the system is getting buffeted by winds, and the jaggies are due to the absolute encoders trying to quickly make corrections.  But I would be interested in other thoughts.

For tonight, I'm going to image the same field, but I've parked my motorhome up wind of the mount to act as a block.  The motorhome is parked 90 degrees to the prevailing wind, and is as close as I can get it while still keeping the roof at about 20 degrees elevation from the scope.  We are forecast for similar winds tonight, and the wind today seems consistent with yesterday.  I'll be curious to see if the results improve.  I'm not sure yet if turbulence as wind goes over and around the motorhome will be more than offset by sheltering the mount.

I am planning for an observatory, and have been thinking all along of a roll-off roof.  I suppose that if tonight's data looks good, perhaps I should be thinking about a dome.  Since I'm not planning on building the observatory until next year, I am also planning on experimenting with different wind blocks (presuming I can find something less than the motorhome, which can stand up to our winds on a regular basis).

If anyone else has dealt with this, I would be interested in how people have dealt with this.  I suppose that I could switch to only wide field imaging during the windiest times of the year, but if possible, I would like to mitigate things.

-Wade


--
Roland Christen
Astro-Physics

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