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azure1961p
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Reged: 01/17/09

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Jupiter, Dec. 28, 2012, 10:00pm
      #5593486 - 12/28/12 10:47 PM



The seeing was lousy but not atrocious at 5/10 Pickering and transparency was a little compromised but still a non issue.

he big thing tonight is that I moved the boundary layer fan so the airflow is directly over the surface of the mirror itself instead of too high above it and no help at all. The upshot is that the results were so good, the idea of a boundary layer fan AND rear blower fan is not an option. My scope anyway HAS to have it. Alan Adler sais he can get by with a boundary layer fan only and thats fin for his thin flex-mirror, however my thick 8" primary really rruly benefits from both fans running. Ive never seen the primaries and secondaries silohette so *unpolluted* as tonight when I was collimating with a defocused Rigel. he cauldrun was gone! Instead, now I see my hand thermals interupting the lightpath, my breath, etc. Im working on that however. Just out of curioisity I reverted to my old way of observing back in the day with no fan running during the observation - it didnt taker long; the gallilean moons slowly but surely began flaring all over the place. There was flare with the fan running, but it EASILY doubled when I cut the power. I instinctively tried refocuisng all fior naught. To think I used to blame it all on the atmosphere - and not even THAT long ago. Boundary layer removal and fan back cooling is not an option. If theres anyone considering it - its so worth it. the galillean moons were the perfect test subjects for this. Without the rear fan blowing the effect was less apparent but still real while again, turning off the power was - forget it you wouldnt go back!!!

well the seeing was ... ehhh tonight at 5/10 and while the fans are great, theres only so much bad air you can blow away. There was atmospheric refraction evident in the moons of jupiter and while this softened things up quite a bit, there still was some details to be had.

Heres the highlights...

It was really a 173x night but I pushed to 200x in vain hope of seeing something tiny like the white spots clearly and other like sized things. I didnt bother with filters. I should have.

Th white storms read like skip dashed morse code over the GRS with the lighter value spots blurrily forming seperated by the darker polar region grey giving this alternating value look going on. In soft seeing this is as good as its going to get.

The NTB over the GRS is really bold now and clearly crosse4s right over the GRS. This was a nice detail that snapped well when the seeing settled a bit.

The GRS is TINY - and definately differnet hue than the belts. It looks unevenly lit, but thats the way its appeared the last half dozen times out.

The GRS wake seems broader now - the tightness of the festooning within it seems to have softened and the dark *arms* crisscrossing it are broader but softer as well. I saw several chambers divided by these slanting SEB interiror festoon like things.

Festoons were awash tonight with the seeings softening and the atmospheric refraction weakening intensities - the *monolith* wasnt seen beside the little grs either. The entire EZ was a gentle smear.

The NEB was lumpy on both north and south edges but no interior details noted.

The moons, again with the fans running were sofy defined but not horrendous. Even at 200x the red/white/blue of the atmospheric refraction was a fairly regular or steady thing.

The seeing was a shrug but the effectiveness of a propelry working boundary fan finally adjusted correctly was neat.

Pete


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: azure1961p]
      #5593837 - 12/29/12 06:30 AM

So, you found a good combo for your fans. Cool. And that it improved your view to be limited by atmospheric seeing is also a bonus. Good on ya.

Yes, the GRS appears two toned much of the time with the southern portion either gray or darker orange depending on the transparency and eye adaption, probably.

You meant the STB jetting out in front of the GRS. Yea, that belt is making some progress.

Seems the textbook festoons are gone, now they are pretty much darker smudges up against the NEB. The entire EZ is awash with a bunch of clouds doing this or that.

But you got our braving the cold. Good on ya, doubly so.


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azure1961p
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Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: Asbytec]
      #5594250 - 12/29/12 11:57 AM

I'm glad I finally blew off the boundary layer - that was a big thing for me! I went years with it in place and always wished it were gone and then so many folks saying its a fact of life and ignore it - particularly in the early and pre Internet times. It was the online buzz here that got me informed then motivated to fix it. Crummy seeing is stil crummy but its definately improved its Pickering value. Ill never get an airless thermal state but its really taken a stride forward.

An interesting thing is what I actually managed WITHOUT the fans - resolving Titan, detail on Ganymede, beyond Dawes doubles etc. I think what's happening here now then is that Ill be able to achieve those leves of res more often as a lot has been negated now. I remember trying Titan sooooooany times and the disc was seen but multiply lensed and flairing every which way. And all along Im blaming the seeing. And again its still relevant but the sheer intensity of it is nicely reduced - probably by half or more?

Pete


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george golitzin
Carpal Tunnel
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Reged: 02/24/06

Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: azure1961p]
      #5594428 - 12/29/12 01:32 PM

Interesting report! You bet, the boundary layer is key. What I find interesting is that, once you conquered the thermal problem, you were able to pick out a lot of detail on the planet despite mediocre seeing--anytime you can see those little white ovals, you're doing great. That really highlights the importance of thermal management, in my view. So yes, I bet you'll see a lot more detail more easily now, even when the seeing is so-so. Maybe more to the point, you'll get detail without having to wait forever for your mirror to cool thoroughly.

-George


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Dean Norris
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Reged: 11/05/08

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Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: george golitzin]
      #5594640 - 12/29/12 03:47 PM

Pete,

I've considered the fan blowing across the mirror in the past and have balked at doing this because the thought cutting a hole for the fan and exhaust holes for ventilation seemed extreme!. I have read Adler's article a few times and have also read a more recent article by Brian Greer that said if your mirror is thicker than 1.5 inches, the fan blowing across the mirror might be needed as well as the rear fan blowing on the mirror. My mirror is 1.5" so it doesn't fit the criteria though I would probably do it if I knew the benefit would be substantial. Also the climate your observing in also plays a role and where the scope is stored contributes to cool down time. I do use a rear fan blowing on the primary and have got good results with this but I'm always looking for ways to improve the image. I would love to see some images of your scope with the new fans.

Sounds like there's some interesting changes on Jupiter. That's great you picked up the small ovals in the SSTB. I haven't seen these yet and hope I get a chance before Jupiter gets too small.

Thanks for posting. Dean


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: Dean Norris]
      #5594990 - 12/29/12 07:35 PM

What George said, if you can pick out tiny, low contrast ovals in mediocre seeing you did something right. In normally above average seeing, they flicker in and out. Usually I can get one or two of the larger ones (in a 6") or the ones showing better contrast set against a darker cloud. I imagine that would be a little easier in an 8", but seeing can definitely wipe them clean.

I dunno Pete, we always look for that magic pill that optimizes our scope just a little. Sounds like you found one that does the trick nicely. (I read your report in the reflector column, but really don't have much to add other than side blowing does seem a more direct way to wipe off that boundary layer. After all, it's not air velocity that impacts seeing, it's air density. A smooth gradient in a hurricane would give great seeing.

Dean, I'd think any mirror that displayed a boundary layer would benefit. They are probably saying thinner mirrors cool faster and it is less of a problem after a period of time. But, if the ambient temps change, so do the conditions inside the tube that produce the layer despite the mirror's thickness.


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azure1961p
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Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: Dean Norris]
      #5594992 - 12/29/12 07:36 PM

Greer was a little too generous in the 1.5" thickness as mine is perhaps an inch to an inch and a quarter and its an issue. The good news as you know is that a rear fan alone is a biggg help. I wouldn't say adding a boundary fan is a huge difference but the flairing is lessened and it completes the thermal reduction issues. Both removed is a big difference indeed.

I know you were reluctant to put a hole in your Cave but you have the rear going do that's a good thing.

Pete


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george golitzin
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Reged: 02/24/06

Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: azure1961p]
      #5595475 - 12/30/12 02:06 AM

I guess the big variables are mirror mass--or perhaps, mass to surface area--and the amount of ambient temperature change. Of course, the latter depends on where you live; here in Petaluma, I find my 8-inch mirror, which is 1.25 inches thick, usually cools to ambient pretty quickly; Dean is in Santa Cruz, where, if I recall (been a while since I lived there), the change in temperature after sunset is mitigated by the coastal environment. I forget where you live, Pete, but you might be experiencing larger temperature differentials, and hence getting a lot more mileage out of your boundary fan. Where it's most dramatic for me is on my 18-inch (which is 2 inches thick): I'll see benefits for hours on end by blowing a fan on the front surface. My 10-inch, which is only 1 inch thick, gets help early in the evening from the face fan, but it's less important once the mirror has cooled.

-geo


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: george golitzin]
      #5595563 - 12/30/12 04:24 AM

You should think also of the mirror cell.
Indeed the 3 points cell needs to be avoided.
But consider also the fact of the 6 or 9points cell supporting a thin mirror. The flexions involved by the system may not even perceptible in perfect seeings. An excellent mirror say ptv 10 may be destroyed even with a such cell that does at final only a ptv5 for example.
This should be analysed carefully, not only by computing but on sky. 200mm is easy to push at 500x even under average skies.
Thin mirror cool faster indeed and the tube design is also important.
You may think a clear open optic will solve the situation as the zambuto photo. This can work under dry nights with no moisture deposition and no observer close to the optics.
This is not a solution.
I found personnally the plain tube made of resin (parks for instance) the best solution and closed with a parallel faces window at the front for limiting the air exchanges with outside. With injection of dry neutral gaz inside, you solve almost the instrumental seeing, the air currents for the most.
After the thickness of the mirror has a relative importance hidden by the tube design.
When the scope is permanently installed outside, temperature equilibrium becomes not a problem.
I did this on a 200mm Cave in the 80ies and this worked fine, and the problem was rejected to the site observation quality and the local seeing only. A step of the seeing levels was almost annealed. Seeing being composed with the instrumental, the local and the altitude seeings.
I think what is usually attributed to the site observation is actually more coming from the instrumental seeing, in fact the more nefast step.
Yesterday evening I was with the 235 cassegrain with an open tube always settled outside, images were 4-5/10 only, almost no air currents inside the tube (short) and jupiter was at 200x almost stable at the eyepiece and the contrasts blurred by the high altitude seeing. GRS was colored and distinct with the tropical band with lot of festons, etc...
Not necessary to go to the 305mm this was with less features.
The cassegrain mirror is a glass bloc that doesnot be subject to flexions.
A last point, little ptv involves more sensitivity to seeing that is normal.
Hope this is an help for anybody.
Stanislas-Jean


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ericj
professor emeritus


Reged: 02/17/05

Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: azure1961p]
      #5597814 - 12/31/12 11:49 AM

Hi Pete,

Interesting report, thanks for posting it.

Sounds like the fans are a big help in dealing with the boundary layer.

Best,

Eric Jamison


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: stanislas-jean]
      #5599673 - 01/01/13 01:56 PM

Quote:

You should think also of the mirror cell.
Indeed the 3 points cell needs to be avoided.
But consider also the fact of the 6 or 9points cell supporting a thin mirror. The flexions involved by the system may not even perceptible in perfect seeings. An excellent mirror say ptv 10 may be destroyed even with a such cell that does at final only a ptv5 for example.
This should be analysed carefully, not only by computing but on sky. 200mm is easy to push at 500x even under average skies.
Thin mirror cool faster indeed and the tube design is also important.
You may think a clear open optic will solve the situation as the zambuto photo. This can work under dry nights with no moisture deposition and no observer close to the optics.
This is not a solution.
I found personnally the plain tube made of resin (parks for instance) the best solution and closed with a parallel faces window at the front for limiting the air exchanges with outside. With injection of dry neutral gaz inside, you solve almost the instrumental seeing, the air currents for the most.
After the thickness of the mirror has a relative importance hidden by the tube design.
When the scope is permanently installed outside, temperature equilibrium becomes not a problem.
I did this on a 200mm Cave in the 80ies and this worked fine, and the problem was rejected to the site observation quality and the local seeing only. A step of the seeing levels was almost annealed. Seeing being composed with the instrumental, the local and the altitude seeings.
I think what is usually attributed to the site observation is actually more coming from the instrumental seeing, in fact the more nefast step.
Yesterday evening I was with the 235 cassegrain with an open tube always settled outside, images were 4-5/10 only, almost no air currents inside the tube (short) and jupiter was at 200x almost stable at the eyepiece and the contrasts blurred by the high altitude seeing. GRS was colored and distinct with the tropical band with lot of festons, etc...
Not necessary to go to the 305mm this was with less features.
The cassegrain mirror is a glass bloc that doesnot be subject to flexions.
A last point, little ptv involves more sensitivity to seeing that is normal.
Hope this is an help for anybody.
Stanislas-Jean




The idea of a nitrogen filled reflector is nice until you realize the amount of construction needed to keep the nitrogen from leaking. The focuser would be the biggest problem even if a window existed at the end of the draw tube. Then there's the collimating screws needing gaskets to keep the screws from leaking as well. A pressurized nitrogen filled reflector would be heavy and costly. The idea is nice but the mechanics are problematic.

Pete


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: ericj]
      #5599679 - 01/01/13 01:58 PM

Quote:

Hi Pete,

Interesting report, thanks for posting it.

Sounds like the fans are a big help in dealing with the boundary layer.

Best,

Eric Jamison




Well now they are but the first installation was a total failure. I'm eager to get some decent seeing to really make some gains. Thanks Eric!!

Pete


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ericj
professor emeritus


Reged: 02/17/05

Re: Jupiter, Dec. 28, 2012, 10:00pm new [Re: azure1961p]
      #5608234 - 01/06/13 12:17 PM

Hi Pete,

I hear you about seeing decent seeing. I was out last night observing Jupiter and the seeing was mostly soft so it was tough trying to pick up the finer detail.

Oh well we both get some decent seeing one of these days.

Best,

Eric


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