AP1100AE PHD2 guiding with wind


ap@CaptivePhotons.com
 

Been a lot of PHD2 discussion recently, so what's one more... 

Dry season is starting soon here with more clear skies, but it usually comes with some wind.

I realize the real fix for wind is a wind break, but some of us just have to be out in it... 

So far I am getting really good guiding, 0.20-0.30 if the wind is calm and the seeing good.  I've hit 0.18" at times for goodly periods.  Really good, and not very sensitive either, I have tried short exposures, long exposures, with a model, without a model. I am sure I could screw it up, but all the reasonable stuff just works.

But the season change brings me to the question: Is there anything you would recommend changing to respond to light wind, the kind that moves the OTA around a bit, say 3-8mph with a C11 and dew shield on it.  In particular do shorter exposures help, or do they fight the encoders?  Longer?  Bigger min moves? 

I do realize the encoders only "see" movement within the mount's mechanism, not shifts that also involve the tripod, etc.  And some of that movement is brief impulse that bounces back, and some may be an actual shift that guiding has to take out.  It's not a simple issue. 

That's why I am wondering if experience has any guidance for the best approach in calm vs windy?

My first inclination is do nothing, but there are folks out there who have probably seen and fought every problem so... advice?

Linwood

PS. And yes, when Is see a girl with a dog on a bicycle blowing past, I will bring the mount inside.


Roland Christen
 

Windscreen is most effective.

Rolando



-----Original Message-----
From: ap@... <ap@...>
To: main@ap-gto.groups.io
Sent: Wed, Oct 13, 2021 7:50 pm
Subject: [ap-gto] AP1100AE PHD2 guiding with wind

Been a lot of PHD2 discussion recently, so what's one more... 

Dry season is starting soon here with more clear skies, but it usually comes with some wind.

I realize the real fix for wind is a wind break, but some of us just have to be out in it... 

So far I am getting really good guiding, 0.20-0.30 if the wind is calm and the seeing good.  I've hit 0.18" at times for goodly periods.  Really good, and not very sensitive either, I have tried short exposures, long exposures, with a model, without a model. I am sure I could screw it up, but all the reasonable stuff just works.

But the season change brings me to the question: Is there anything you would recommend changing to respond to light wind, the kind that moves the OTA around a bit, say 3-8mph with a C11 and dew shield on it.  In particular do shorter exposures help, or do they fight the encoders?  Longer?  Bigger min moves? 

I do realize the encoders only "see" movement within the mount's mechanism, not shifts that also involve the tripod, etc.  And some of that movement is brief impulse that bounces back, and some may be an actual shift that guiding has to take out.  It's not a simple issue. 
That's why I am wondering if experience has any guidance for the best approach in calm vs windy?

My first inclination is do nothing, but there are folks out there who have probably seen and fought every problem so... advice?
Linwood

PS. And yes, when Is see a girl with a dog on a bicycle blowing past, I will bring the mount inside.

--
Roland Christen
Astro-Physics


Robert Berta
 

Roland is right....a windscreen is first thing to consider. Of course a dome or roll off roof observatory helps but when I move away from my home setup to a star party I have a few tricks and things I have noticed.

First....I have a 1100 that is used interchangeably with a 11" SCT and Hyperstar and a 6" APO refractor. With a guide scope and various equipment both are fairly close in weight. I noticed that the 11" with dew shield tends to be more susceptible to wind gust issues than the 6" refractor. The 11" with the large dew shield has a larger sail area although the refractor is longer.
Some things I do to minimize wind includes positioning my full size van as a wind break. My mount in the field at star parties uses a modified Meade Giant Field tripod rather than the pier I use at home as it is easier to deal with uneven ground. I setup on grass (eliminate effects of heat off paving) but to prevent the mount from sinking into the ground and screwing up polar alignment, I use 12" squares of plywood under each leg (can also be used with a portable pier) and sometimes set the tripod leg tips on antivibration pads from Celestron (other companies also have them). Besides cutting vibration down to at least half of what it was before, they also work to fight the effects of wind gusts. They consist of an inner and outer cup of hard plastic with a Sorbothane filling that acts as a very effective damper. Placing a metal tripod leg tip on concrete or blacktop will make vibration worse. On grass/dirt  a piece of wood or the even better, the antivibration pads will interrupt the hard connection with the ground and dampen vibration. Some tripod tips are bare metal...others have rubber tips which is better but not as good as the antivibration pads.


ap@CaptivePhotons.com
 

Robert Berta wrote:

  • Roland is right....a windscreen is first thing to consider. Of course a dome or roll off roof observatory helps but when I move away from my home setup to a star party I have a few tricks and things I have noticed.

I actually built one last winter, heavy 2" PVC, heavy moving blankets hanging to take the energy out of the wind.  It did help, until one night the 3-5mph gusted maybe 15-25 and blew it over and tore it apart.  Staking it down would solve that of course, but I also found out how much trouble it was to erect and remove every day.  I' may go there again, but not looking forward to it.  It's hassle enough to set up the mount and OTA.

I'm completely prevented from anything permanent by HOA rules. I investigated putting in a natural hedge barrier to put the telescope inside -- nope.

I need to move. 

  • First....I have a 1100 that is used interchangeably with a 11" SCT and Hyperstar and a 6" APO refractor.

A 6" APO is next on my wish list.  Jealous. 

  • (Vibration dampening steps)

I've actually become a big fan of my wooden (Berlebach) tripod.  I had metal before, and I find wood much more "dead".  I set up nice beds for three pavers, with sand and gravel beneath them, and away from any foot or road traffic. A nice side effect is dropping the tripod spikes in holes in the pavers I land within a few arc minutes of polar aligned before I even start. Plus these wide connections at the top I think help kill torsion much better than the like tube-in-bigger-tube of some tripods for legs.

But until I get energetic again and build a new wind screen, and buy into erecting it each day, and taking it down… I was curious if there are guiding settings that work best.  I guess I'll find out as the season picks up.  One advantage this year is I have a anemometer near the mount, so I can look back and if some subs are bad, or guiding bad, I can confirm if the wind changed.  Also wakes me up if a raindrop hits, stratum 1 time server, etc.  I'd call it "Astro" the three legged dog but Astro-Physics may object. 😊

Thank you!

Linwood