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stanislas-jean
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Reged: 10/22/08

Re: Uranus cloud bands in a C8 new [Re: t.r.]
      #5498024 - 10/31/12 04:15 PM

Apart to show always past photo from hst, lot of years ago, etc... you bring so few.
I am sorry of this, frankly. Now If you want to get some adequate answers that suits you, I guess you read all the posts and those of the forum 3 screens back on the planetary and solar system forums, same subject, "Uranus season is open".
Good read, pick up Mr Mullet with you.
Sorry, the day was very bad as in NYC, but on other fields.
Stanislas-Jean


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David Knisely
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Re: Uranus cloud bands in a C8 new [Re: stanislas-jean]
      #5498144 - 10/31/12 05:41 PM

stanislas-jean wrote:

Quote:

This means your 250mm of the described characteristics will be equivalent to 192mm clear perfect diameter.




No, the resolution of the instrument is still that of a 250mm clear aperture, so a 10 inch remains a 10 inch. The central obstruction definitely does have an effect, but the common idea of subtracting the secondary's minor axis from the primary diameter is not strictly valid, especially when the obstruction remains fairly modest. Indeed, the light blockage of my 10 inch Newtonian's secondary (2.14 inch minor axis) would make my 10 inch's light gathering ability into an "equivalent" 9.768 inch (248 mm) aperture's light gathering ability. The contrast reduction caused by obstructions in the 20% to 25% range is fairly small and does *not* affect the instrument's resolution. When the obstruction approaches or exceeds 30% is when the central obstruction really starts to impact the contrast of fine low contrast detail (see Suiter's book "Star Testing Astronomical Telescopes" 1st edition, p. 155-157). Most Cassegrain systems have central obstructions in the 29% to 36% range, so for those instruments, that larger secondary obstruction is a very significant factor in reducing the contrast of fine detail.

However, this is all getting well off the topic. If one is looking for a reason why I am seeing little on Uranus with good instruments under halfway decent conditions, well, there is, of course, a possible (and obvious) explanation.....


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t.r.
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Re: Uranus cloud bands in a C8 new [Re: David Knisely]
      #5498171 - 10/31/12 05:58 PM

Stanislas, have you made any of your observations using filters? According to ALPO colored filters are highly recommended in order to see any detail..."Uranus and Neptune: Yellow-green (W12), green (W57), and magenta (W30) filters are recommended on these bluish and greenish planets. Because both planets are much dimmer than the others in the telescope it suggests the Purkinje, Bezold-Brucke, Tritanomalous vision effects may be at work here. Observing these planets is difficult and their blue-greenish color begins to change to a bright blue using moderate to large aperture telescope (12- to 24-inches)". Because of vision limitations, I read that filters are a necessity to have any chance of success.

EDIT: Okay, I do see in one of your old post you use at least one filter #8.

Edited by t.r. (10/31/12 08:10 PM)


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Rick Woods
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Re: Uranus cloud bands in a C8 new [Re: t.r.]
      #5498310 - 10/31/12 07:17 PM

"Did so!"
"Did not!"
"Did so!"
"Did not!"
"Did so!"
"Did not!"
"Did so!"
"Did not!"

Jeez...


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Rick Woods
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Re: Uranus cloud bands in a C8 new [Re: David Knisely]
      #5498315 - 10/31/12 07:19 PM

Quote:

Sir, are you challenging my observations?




Well, to be fair, David, you're challenging his.


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telescopemullet
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Reged: 11/16/09

Re: Uranus cloud bands in a C8 new [Re: Rick Woods]
      #5498340 - 10/31/12 07:39 PM

Correctly so as Stan is drawing nothing more than his imagination.

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David Knisely
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Re: Uranus cloud bands in a C8 new [Re: Rick Woods]
      #5498393 - 10/31/12 08:17 PM

Quote:

Quote:

Sir, are you challenging my observations?




Well, to be fair, David, you're challenging his.




No, the poster was not being at all clear about what he was talking about. It appeared that he was challenging me based on the fact that I did not provide the precise figures for the optical quality of my equipment, which is a very bad way to approach things. Clear skies to you.


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starrancher
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Reged: 06/09/09

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Re: Uranus cloud bands in a C8 new [Re: Rick Woods]
      #5498472 - 10/31/12 09:13 PM

Quote:

"Did so!"
"Did not!"
"Did so!"
"Did not!"
"Did so!"
"Did not!"
"Did so!"
"Did not!"

Jeez...







Oh , one more thing .
What the heck is a Mullet ?
Is that some kind of "Achy Breaky" thing ?


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orion61

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Re: Uranus cloud bands in a C8 new [Re: CPellier]
      #5498495 - 10/31/12 09:31 PM

We all seem to forget that in moments of absolute perfect seeing the eye of someone with 20/15, 20/10 vision will still see detail not caught imaging. You can process all you want but stacking is still stacking and that is an Average of images. There are some of us that can pick out the phase of Venus at its (near) closest point with the naked eye..
And yet in the end we all agree to disagree.


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Asbytec
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Re: Uranus cloud bands in a C8 new [Re: orion61]
      #5498635 - 10/31/12 10:52 PM

The 2% contrast on the planet and 1% contrast transfer through a very good scope requires exceptionally perfect eye's with amazing capabilities, such as seeing into the near IR (if the features are present that close to the visual spectrum.)

Especially on a bright, low contrast target like Uranus and at the line frequencies involved. It seems any CO at all would simply wipe out contrast to below the level of ambient noise. Uranus is exceptionally difficult to observe, in my experience, and fluctuations in albedo due to seeing can be seen.

But, if it can be done, it can be done by someone with amazing abilities. I can't do it, certainly not in a 6". Others can't do it in larger scopes. So, "...in the end we all agree to disagree."

I am just not entirely convinced it's even technically possible to visually detect far IR features at those contrast levels in any scope. But, his observation are his observations, as reported, we have to accept them for what they are, as reported. Nothing wrong with skepticism. Some folks do not believe in Big Foot.


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azure1961p
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Re: Uranus cloud bands in a C8 new [Re: orion61]
      #5498804 - 11/01/12 12:46 AM

Quote:

We all seem to forget that in moments of absolute perfect seeing the eye of someone with 20/15, 20/10 vision will still see detail not caught imaging. You can process all you want but stacking is still stacking and that is an Average of images. There are some of us that can pick out the phase of Venus at its (near) closest point with the naked eye..
And yet in the end we all agree to disagree.




That's not really applicable here. The simple fact is that specifically on Uranus simple eye versus ccd isn't typical of the comparison you make which is still only partially true. Today's imagers are actually naturally infra red sensitive in a way the eye is not. Indeed, IR CUT filters are often needed to help preserve contrast in a way not affected by infra red. On Uranus then, sans the IR CUT , then the Imaging system has a distinct advantage over the human visual sensitivity. While a dielectric diagonal will negate this, the typical straight thru ccd setups have no such issues.
So while in daylight perhaps there is an advantage in human visual over ccd (though not all people ever) there are distinct imaging sensitivity attributes that no person can compete with.

Pete


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azure1961p
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Re: Uranus cloud bands in a C8 new [Re: stanislas-jean]
      #5498815 - 11/01/12 12:59 AM

Quote:

This means your 250mm of the described characteristics will be equivalent to 192mm clear perfect diameter. Then you can evaluate the scope transfer contrast ratio by FTM curves and the expected contrast level at the eyepiece which is in this case around the 1% level (for 2% on the planet itself).
This is the situation (the seeing level considered perfect).
Is it possible?
The numbers given may be discussed, especially the actual contrast feature on the planet.
Stanislas-Jean




I'm a little disappointed with your reply here Stan. You posed the statements that without an observer (we'll call him... Dave) having absolute knowledge of the degree of excellence of his instrument that an argument against your position cannot be mounted. Then, in the face of that an observer (we'll call...) makes all measures of his instruments optics, strehl wave and so on to a decimal point and look what you do - you skipped right around it, made some erroneous remarks about aperture resolution and turned a total blind side to the fact that he substantiated his original claims meeting the requirements you initially stated.

With evasive jukes and dodges like this you make your positions elusive.

Pete


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Uranus cloud bands in a C8 new [Re: azure1961p]
      #5498920 - 11/01/12 05:06 AM

Making no effort for understanding or try to, no surprise.
David 192mm is not for resolutioon, resolution you have enough. This is for contrast level for the evaluation of a contrast transfer ratio applied on grey line feature. For 1" width this will do 50% ratio so from a 2% level this will do 1% at the eyepiece.
Do you capture? TR as well, for Mr Mullet he is a mullet with his science of 2 pennies, he captures nothing and read nothing but he is so true.
You have all the explanations necessary published on the japanese alpo site with the assessment for the Uranus observation under a mesopic vision because this is a mesopic mode, otherwise you are blinds.
Make some efforts guys, when i am researching something i find a response or a partial one, you, everything has to be brought on a dish with the bended body attitude.
Stanislas-Jean


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t.r.
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Re: Uranus cloud bands in a C8 new [Re: stanislas-jean]
      #5499000 - 11/01/12 08:02 AM

Again Stan, I DO believe you and others are seeing something...but you cannot and will not concede that it may be illusory. That is the issue. Even O'Meara agrees with this. The science and the numbers are still against you...regardless of your assertion to the contrary. I think this is now at the parallel of arguing politics and religion. Good luck with your future observing program and clear skies.

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John Boudreau
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Reged: 04/06/08

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Re: Uranus cloud bands in a C8 new [Re: orion61]
      #5499201 - 11/01/12 11:01 AM

Quote:

We all seem to forget that in moments of absolute perfect seeing the eye of someone with 20/15, 20/10 vision will still see detail not caught imaging. You can process all you want but stacking is still stacking and that is an Average of images. There are some of us that can pick out the phase of Venus at its (near) closest point with the naked eye..
And yet in the end we all agree to disagree.




While the stacked result of the selected frames is indeed an average, it's important to note that with proper use of the stacking software only the best frames need be selected for processing and the enhancement techniques applied by an experienced imager will always beat visual given the same seeing conditions. Some processing software even allows manual override of frame selection which while tedious, can further widen the gap between imaging and visual.

For instance, it's a lot easier to detect the Encke Gap with imaging even in less than perfect seeing. Spokes in Saturn's rings were almost routinely imaged during the storm of late 2010 through the first half of 2011. Sub-arcsecond details are reliably recorded on the moons of Jupiter with regularity, again even in less than perfect conditions. And you won't visually see features on Mercury with the consistency of those shown in my avatar, and I've done better than that in recent years.

Besides even if one chooses to discount all that, we also have visual-band HST images of Uranus that are featureless. I don't think many would believe that a skilled observer could see features beyond the range of the HST.

Seems that some simply want to discount seeing and spectral dispersion effects on a small angular target. And nobody is immune to optical illusions, which shouldn't be discounted as a possibility either. Uranus is such a bland target that it may well provide a perfect canvas for observing problems that would normally be overpowered by relatively high contrast features on other planets. Stan isn't the only guy reporting bands, and there have been such observations for many years:

Observations Of The Planet Uranus With The 36-inch Equato...

Back when those Lick observations were made the polar orientation of Uranus was not known. Today observers know the true orientation very accurately. I wonder how the Lick drawings would appear if the observers already knew the planet's true orientation at the time?

BTW--- As has been mentioned by others, the problem here is are there features on Uranus that can be seen routinely even in average seeing? I definitely think not, but I do think at rare times visual spots or other features can occur on Uranus.


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Uranus cloud bands in a C8 new [Re: John Boudreau]
      #5499322 - 11/01/12 12:09 PM

The problem on that kind of subject, John, may I be disapointed by them?
In fact the main channel to conduct conclusions are always the same, all based on a certain experience of problems, very serriously for some and for some others faintaisist even reported by recognised people.
I think on this planet there are also observers, not me, who report something seriously with precautions and cautious with the wording hold (see the BAA section).
The hst images are done in a certain manner, we don't know how. And not sure also that the 1-2% contrast level is well researched or shown. Honestly I don't know apart the views publishedd widely. There are also some others that report variabilities, sometimes level contrasts, so not the landscape you are describing in your post.
Now I donot think the problem can be discarded as you said.
You see in order to be more confortable with some views. Some different assessment methods can be undertaken to see if the question is reachable.
I think very few did this approach in the past and from these recognised people that injured a lot what they cannot approach themselves.
Starting from the investigation on publications on the subject some data were reported in IR and NIR. From it can be expected some contrast levels reachable in the visual field.
We know the fields of the methane absorption bands accessible, the G and R, the G is too confidential.
We know for capturing something on this planet the mesopic vision with its properties needs to be satisfied in terms of resolution contrast levels. We have to-day lot of data published in that fields.
The diffraction laws help today to assess the scope influence in term of degradation, sothat some contrasts at the eyepiece can be asseessed.
Now against these possibibilities it remains our own abilities through tests also that must respect the light levels during observations and the expected feature sizing.
How? Long distance cible observation with known contrast of features lighted by the full moom light only (this was found to be similar on the target).
Test at a Laboratory of yourself with a testing machine (roughly the observation of parallel lines with a sinusoidal grey tone law, the same usable for FTM tests).
The test was conducted until the test pattern having max 2-3% contrats under the similar light level of the planet surface.
If this is not science, amateur, tell me what is science against experience so well recognised.
The conclusion was what: publications gave the conclusion that contrast can be expected at this level, the mesopic vision can support such target, Lab tests and long distance tests demonstrated this ability and now the planet reports are giving what you see.
This is largely better than sp[eaking with experience that means nothing at the 1st approach.
The planet offers the possibility of getting something in R color and under the characteristics given above.
Now, on this alpo japanese site, I guess you to consult ALL the documents because some observers are imaging in pure R channel only and report banding. One observer reported the dark collar near the polar cap in blue channel where the features are recognised to be unexistant.
Artefacts, the method of 90 degree rotation between acquisition were lead aso. My conclusion is artifact when some are unable to make similar at the same level. Views are more lead by ego than by normal analysis of situations.
I am sorry by this architecture given above was already given in past in the forum "uranus season is open".
This is this global system that makes the pertinence not the fuzzy idea of experience.
Stanislas-Jean


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Uranus cloud bands in a C8 new [Re: t.r.]
      #5499337 - 11/01/12 12:16 PM

TR if you consider the appoach of religion in that debate, I think regarding the results given they are not far from some actuallity reported by very great scopes.
Do you feel that I am on the right way for getting the illumination!
Sorry
Stanislas-Jean


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David Knisely
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Re: Uranus cloud bands in a C8 new [Re: stanislas-jean]
      #5500292 - 11/02/12 01:11 AM

Quote:

David 192mm is not for resolutioon, resolution you have enough. This is for contrast level for the evaluation of a contrast transfer ratio applied on grey line feature. For 1" width this will do 50% ratio so from a 2% level this will do 1% at the eyepiece.




You are not making yourself clear at all here. What is the size of the central obstruction of your 305 mm Cassegrain and what type of Cassegrain is it? If the central obstruction is significantly more than 25% of the primary's diameter (which I suspect it is), then you are working at much more of a handicap in terms of reduction in contrast of fine features than I ever do. Despite multiple observations, I do not see any markings on the disk of Uranus currently in my 14 inch and never have in any of the other instruments I have used either. I just don't feel there is much to see there. Clear skies to you.


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stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Uranus cloud bands in a C8 new [Re: David Knisely]
      #5500429 - 11/02/12 05:42 AM Attachment (27 downloads)

Here is the last observation of Uranus performed last 1st November.
Only 10 minuts of sky aperture for this exercise with the 305mm cassegrain under a cristallic sky between cloud formations.
Average images to good on short periods.
It was not possible to get more, the magnification being too low for capturing the albedo variations or brightnings, light glare being too present for the exercise.
Faithfully.
Stanislas


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azure1961p
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Re: Uranus cloud bands in a C8 new [Re: stanislas-jean]
      #5500885 - 11/02/12 12:41 PM

And that concludes the thread.

P.


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