Go Back   IceInSpace > Equipment > DIY Observatories

Reply
 
Thread Tools Rate Thread
  #61  
Old 02-05-2020, 08:22 AM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
So a question, I'd be interested to hear the opinions of you ladies and gents on whether or not you think putting the scope at 8-9m above ground is a waste of effort in terms of getting better resolution images. I've read and heard that getting above the ground based level seeing conditions has a positive effect on the FWHM of your images.
Who thinks it's possible compared to having the scope at ground level?


Josh
Reply With Quote
  #62  
Old 02-05-2020, 10:33 AM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,625
Incredible attention to detail Joshua. Love the weather system, cabling and dust extractor. It is almost a military installation. Nice work and I am sure once you have it airborne it will produce years of service. Just one thing. Make sure you can reach the AAG cloud sensor. I am on my third one in 12 years. I run my continuously which is recommended but wonder if that lessens the life of the units.

As to the seeing effects at ground as opposed to 8 meters up; whilst I have read there can be significant gains made it would depend on the size of the scope installed, what the focal length/image scale will be and the local seeing conditions. I suppose it also really depends on what you intend to do with the system in the long run. Is this going to be a research grade system, will you be trying to attract scientists to use the equipment at hire? If not I guess you have to ask yourself if it is worth the effort to elevate the rig. Can't answer that for you.
Reply With Quote
  #63  
Old 02-05-2020, 04:18 PM
noswonky (Peter)
Registered User

noswonky is offline
 
Join Date: Jul 2010
Location: Blue Mountains, NSW
Posts: 142
Quote:
Originally Posted by Joshua Bunn View Post
So a question, I'd be interested to hear the opinions of you ladies and gents on whether or not you think putting the scope at 8-9m above ground is a waste of effort in terms of getting better resolution images. I've read and heard that getting above the ground based level seeing conditions has a positive effect on the FWHM of your images.
Who thinks it's possible compared to having the scope at ground level?

Josh
No personal experience with this, but a couple of years ago we had a professional astronomer speak at our club and he was talking about this issue. His team was operating a small observatory in Antarctica and they had done testing which confirmed that most of the air causing seeing issues was just a few meters off the ground. So they elevated the equipment to get above it.

Of course Antarctica is a very different environment so I donít know if this would apply at other sites.
Reply With Quote
  #64  
Old 03-05-2020, 02:19 PM
marc4darkskies's Avatar
marc4darkskies (Marcus)
Billions and Billions ...

marc4darkskies is offline
 
Join Date: Mar 2007
Location: Quialigo, NSW
Posts: 2,838
Quote:
Originally Posted by Joshua Bunn View Post
So a question, I'd be interested to hear the opinions of you ladies and gents on whether or not you think putting the scope at 8-9m above ground is a waste of effort in terms of getting better resolution images. I've read and heard that getting above the ground based level seeing conditions has a positive effect on the FWHM of your images.
Who thinks it's possible compared to having the scope at ground level?

Josh
Quote:
Originally Posted by Paul Haese View Post
...
As to the seeing effects at ground as opposed to 8 meters up; whilst I have read there can be significant gains made it would depend on the size of the scope installed, what the focal length/image scale will be and the local seeing conditions. I suppose it also really depends on what you intend to do with the system in the long run. Is this going to be a research grade system, will you be trying to attract scientists to use the equipment at hire? If not I guess you have to ask yourself if it is worth the effort to elevate the rig. Can't answer that for you.
What Paul said!

My approach to building an obs has always been entirely empirical and based on half a dozen or so basic dos and don'ts and the number of dollars I have AND the fact that I'm an engineering ignoramus.

Dos & don'ts:
  1. thermal mass is bad, mmm-kay! So no concrete pad for me .... and don't put your obs next to a house (ooops! ... but my excuse #4 below))
  2. a pier footing should be substantial and isolated from the observatory structure
  3. the telescope pier should be >=5mm thick buttressed aluminium or steel tubing anchored to the footing and be about 250mm in diam to minimise deflection and resonance .... and it should NOT have a bird cage on top!!!
  4. should have convenient access (the older you are the more important this becomes!)
  5. should allow adequate ventilation
If I was an engineering genius, like you , would I build a tower obs? Probably not, because I've never seen anything definitive to say that seeing is noticably better at greater than 3m above ground level (the aperture of my scope is about that). I can imagine it may be better, but I'd be guessing that it would be marginal at best compared to normal seeing conditions.

Having said that, unless No. 4 in my list above rings true for you, I'd press on.
Reply With Quote
  #65  
Old 03-05-2020, 07:19 PM
ericwbenson (Eric)
Registered User

ericwbenson is offline
 
Join Date: Sep 2009
Location: Adelaide, Australia
Posts: 206
Hi Joshua,

You mention you have read about ground level seeing, have you seen this article:

Altitude, Elevation and Seeing by Rene Racine
https://ui.adsabs.harvard.edu/abs/20....401R/abstract

In it the author develops a model to account for altitude of the site, and the elevation of the telescope to predict the seeing using data from 23 professional sites (including Siding Springs). His model agrees quite well with the data (~0.1" residuals)

A few years ago I entered the model into a spreadsheet with his best fit parameters, attached is the chart I made.

Notice most of the gain is the first 3 meters.The front of my telescope aperture is about 3m above the ground (in a dome) at 425m above sea-level near Arakaroola, and the best seeing I get is about what the chart says: ~1.1"

So according to model the 425m ASL doesn't do much, but the 3m does, I find this is not exactly what my experience tells me. My C11 or C14 at 2 meters elevation with the dew shield on in my backyard in Adelaide gets way worse seeing on average, although it can be very good (<1.5"), sometimes.

Note his model is possibly optimistic since he used only very good sites to fit the parameters. Sites in compromised areas (cities, rough topography, bad jetstream, etc) may not perform as well.

I think in my case being on a very steep ridge/hill, ~75m above the surrounding area (it's like a 75m tall pier?!?), does have a big impact as it gets the dome above the inversion layer that can form in the area. Compared to observing from the village itself, we know this can make a huge difference which I don't believe is captured in the model.

The problem I would see with higher elevation (very tall exposed pier) is wind shake. Even though you have a small sail area for your tower/pier, the vibrations induced by wind on a long thin member can be difficult, if not impossible to predict. So unfortunately you are entering uncharted territory with this design.

If you build the full height version (6-8m), can you cut it back down to 3-4m if it's too woobly? (I am presuming you have access to a crane to install the darn thing in the first place).

Best,
EB
Attached Thumbnails
Click for full-size image (Seeing vs Elevation and Altitude.jpg)
69.0 KB34 views
Reply With Quote
  #66  
Old 04-05-2020, 12:20 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 16,347
I suppose the end of my larger scopes must be about 2.4 metres off the ground. Hard to say if the ground effects are influencing the images at all or not. What is noticeable is the seeing and its effect on a long focal length scope.

Poor seeing is absolutely shocking and so bad the scope basically can't be focused.

So I suspect its a mild effect. I have put a fan on the scope in the past to disperse any ground effect and I could not see any difference.

I have a small concrete slab, a pier concrete slab that has a lot of steel in it and 914mm deep and about 900 x 900 or so. Then a Pegasus pier which is around 1.2 metres tall then the mount and scope.

Never had a problem from wind or shake or any vibrations. Solid as a rock.

Observatory is lightweight pine framing and colorbond roof and walls with aircell insulation. The roof has gaps around it due to the roll off structure so there is a small amount of airflow through that.

Spiders love the place. So do the mossies.

That's the observatory at home, at my dark site its simply a 200mm x 5mm thick steel pipe set in the ground 600mm and rapid set concrete then pavers for a floor. Again never had issues with vibrations. After all our mounts are well balanced.

Greg.
Reply With Quote
  #67  
Old 06-05-2020, 12:12 AM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
Thankyou for your replies everyone.


Paul, thanks for writing, I dont want to be servicing or pulling it down from that height, so I have to think of as much as i can now

The dust extraction is actually a fan (2 now, one axial the other centrifugal), that blows air into the room and out through small gaps, keeping the inside air pressure a little above atmospheric. Hopefully this keeps out most of the dust.


So it appears true that there are resolution gains, even if small, by elevating the telescope. It will certainly be an interesting first few nights of data capture to see how things go. For sure, to make use of any resolution gains, one would need a telescope that can take advantage of that, and so focal length and image scale play a significant role here.



Ill be imaging at 2.5m F.L. with an image scale of 0.73"/Pix. One of the guys I spoke with was Russell Croman, he has a RCOS 20" in an elevated observatory, and he said he recons he got about (don't quote me or him on this) 0.25" better FWHM in his elevated dome.


Hi Eric, thankyou for writing. I can't say I have seen that article, but that is an interesting graph you have supplied. It's possible i could reduce the height if i really needed to, but that is a lot of work
My first course of action would be to sheet the outer frame in sheet iron to protect the pier from the wind, and see how that goes.


Josh
Reply With Quote
  #68  
Old 08-05-2020, 08:08 AM
Pepper (Steve)
Registered User

Pepper is offline
 
Join Date: Dec 2018
Location: Tamworth
Posts: 235
I may have missed it somewhere but how are you powering this facility? Solar or on the grid?
Reply With Quote
  #69  
Old 08-05-2020, 08:29 AM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
Hi Steve.


I haven't posted that yet, it'll be in the next post. But it will be with 20 solar panels and a lithium ion phosphate battery bank.
Josh
Reply With Quote
  #70  
Old 08-05-2020, 08:57 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 19,676
Impressive fabrication Joshua. You seem to be a jack of all trade. Your workshop looks like a naval shipyard. It's huge. Can't wait to see how it all fits together at height. I like that shaded perspex for the all sky camera.
Reply With Quote
  #71  
Old 08-05-2020, 11:17 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
Thanks Marc. The workshop is great, very fortunate to have the space and equipment to build the observatory. The perspex is kind of experimental, we'll see how it goes 😁
Reply With Quote
  #72  
Old 31-05-2020, 08:01 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
An update for you all who are interested...


The changes from my last post are an undercoate and topcoate of paint everywhere inside and out, white on the outside and flat black on the inside.


The other addition is I have added all the enclosures that will house the electronic equipment and conduit to go between everything and all around the Observatory. All the wires are in conduit for organisation and to keep rodents away from cables. I chose to use large conduit and a junction box on every corner so there will be no problems pulling cables around corners or if I want to add more later on.

I have separate conduit for Ethernet, 240 volt AC and various voltages of DC electrics.
Next is to add the wires, the fun part


The white conduit bellow the enclosures is for air ventilation for cooling electronics, the air comes from the 2 fans in the Observatory, which is pulled from outside.


Cheers Josh
Attached Thumbnails
Click for full-size image (PSX_20200531_184954.jpg)
75.1 KB88 views
Click for full-size image (PSX_20200531_185015.jpg)
142.9 KB87 views
Click for full-size image (PSX_20200531_185031.jpg)
175.4 KB86 views
Click for full-size image (PSX_20200531_185047.jpg)
137.0 KB74 views
Click for full-size image (PSX_20200531_185101.jpg)
197.9 KB80 views
Click for full-size image (PSX_20200531_185119.jpg)
137.8 KB83 views
Click for full-size image (PSX_20200531_185130.jpg)
150.7 KB89 views
Reply With Quote
  #73  
Old 31-05-2020, 08:59 PM
croweater (Richard)
Don't Panic!

croweater is offline
 
Join Date: Feb 2015
Location: Millicent, South Australia
Posts: 312
Wow Joshua, that is impressive . Certainly beats my extension cord and 4 plug power brick
Seriously though that looks great mate. Keeps the posts coming.
Cheers,Richard
Reply With Quote
  #74  
Old 01-06-2020, 01:57 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
Thank you Rick. If that's what works for you, that is awesome 🙂
Thanks for writing
Reply With Quote
  #75  
Old 02-06-2020, 11:52 AM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,625
Man I thought I was a neat freak. Totally awesome looking system setup Josh. It's going to be impressive just on looks alone.
Reply With Quote
  #76  
Old 02-06-2020, 12:23 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
Thanks Paul. I think it's nearly as much about esthetics as it is functionally, who doesn't like organisation, I mean, if something hits the fan, it's easier to diagnose. Could you imagine diagnosing something in a mess of all these wires and components 🙄😂
Reply With Quote
  #77  
Old 02-06-2020, 01:01 PM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,625
Quote:
Originally Posted by Joshua Bunn View Post
......Could you imagine diagnosing something in a mess of all these wires and components ����
Yep, been there before, hence why I got more creative in my cable management. Trying to find cables which are effected by one thing or another is often the biggest part of the problem.

It's going to look very cool in the end.
Reply With Quote
  #78  
Old 02-06-2020, 05:16 PM
jamespierce (James)
Registered User

jamespierce is offline
 
Join Date: Jul 2009
Location: Australia
Posts: 293
The electrical conduits are a work of art. I've tried hard to keep my cabling sane and have redone it several times to tidy it up but it's still messy in places. I love that space under the scope itself as a utility area.
Reply With Quote
  #79  
Old 02-06-2020, 05:19 PM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,221
Thanks James, that's where the PC goes, under the mount.
Reply With Quote
  #80  
Old 02-06-2020, 05:57 PM
strongmanmike's Avatar
strongmanmike (Michael)
Woohoo it's clear

strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
Posts: 15,222
Soooooo, will you he opening the roof by hand Josh

Mike
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 10:56 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Advertisement
Limpet Controller
Advertisement
Testar
Advertisement
NexDome Observatories
Advertisement
Bintel
Advertisement
Astronomy and Electronics Centre
Advertisement