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Equipment Discussions >> Refractors

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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Jupiter in small refractor telescopes
      #6190212 - 11/12/13 09:24 AM

Hello,
the time for watching Jupiter gets better and after a discussion with Alexander about watching Jupiter in small refractor telescopes (e.g. 3 " or 4") I would like to discuss and collect your observation experience. Which details are you able to see? Are you able to see the oval BA? How is the colour seeing of the bands and the Great Red Spot or oval BA?
I had only once the chance to see Jupiter about 4 weeks ago in my 4" 1100 mm achromat. The bands looked rather greyish maybe with a little brown touch and I could imagine that there was a hint of orange in the Great Red Spot and a little bit structure in the two main bands in the short periods of good seeing.
Here a photo taken with the ASI 120 MC and with diagonal mirror (south is at the bottom and west is right) at October 3rd at 6:08 am in Germany.
http://www.cloudynights.com/photopost/data/500/218055saturn2_stretch.jpg
or with brightened moons
http://www.cloudynights.com/photopost/showphoto.php?photo=28589

Clear skies,
Roland

Edited by Niklo (11/12/13 09:34 AM)


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6190237 - 11/12/13 09:45 AM

Here are some of my sketches through 80mm with oval BA from last opposition:

http://www-hep2.fzu.cz/~kupco/astro/2012/2012_11_19/pic/orig/Jupiter_20121119...
http://www-hep2.fzu.cz/~kupco/astro/2012/2012_12_01/pic/orig/Jupiter_20121201...

And here is the similar region through 4" refractor (ED100):

http://www-hep2.fzu.cz/~kupco/astro/2012/2012_11_09/pic/orig/Jupiter_20121109...

Concerning of what I can see through 80mm, this sketch was made during quite good conditions (Antoniady II):

http://www-hep2.fzu.cz/~kupco/astro/2012/2012_12_16/pic/orig/Jupiter_20121216...

And here is a sketch through 100mm in favorable conditions:

http://www-hep2.fzu.cz/~kupco/astro/2012/2012_11_05/pic/orig/Jupiter_20121105...

Even 63mm is not hopeless:

http://www-hep2.fzu.cz/~kupco/astro/2013/2013_03_03/pic/orig/Jupiter_20130303...
http://www-hep2.fzu.cz/~kupco/astro/2012/2012_10_11/pic/orig/Jupiter_20121011...

Concerning the colors, as we discussed with Roland, I can't see too much of color on Jupiter. Even in my former larger 250mm Newtonian I only saw reddish tint of GRS only once. With 80mm I had an interesting experience when I was using white LED for sketching instead of my usual red LED. When I looked into the eyepiece the GRS looked quite reddish, also the main surfaces was yellowish. In few seconds the colors were gone before. I guess my brain is quite effective of removing colors...

Cheers,

Alexander


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Astrojensen
Post Laureate
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6190268 - 11/12/13 10:04 AM

My observations agree with yours, Alexander, though I haven't drawn Jupiter much and am not an expert at drawing planets. I can't recall having seen oval BA, but I do think I've seen it with my 80mm f/15 Vixen. GRS I've seen with even my 50mm Zeiss.


Clear skies!
Thomas, Denmark


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6190295 - 11/12/13 10:13 AM

Hi Thomas hello Alexander,
the oval BA moved to the other side of Jupiter this year but I'll try it with my Vixen 80L f/15, too.
Thomas have you seen a little bit orange in the Great Red Spot with your Vixen 80 or with your Zeiss 85 f/18?
Clear skies,
Roland


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PeterR280
Pooh-Bah
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Reged: 05/27/13

Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6190304 - 11/12/13 10:18 AM

Has anyone noticed contrast variations based on seeing conditions? I recall a few months ago with very good seeing at 5AM, the bands were a much darker brown with a 4" than I am used to.

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David E
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Reged: 05/25/06

Loc: North Carolina
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6190323 - 11/12/13 10:29 AM

Since we are looking at cloud tops, not terrain, Jupiter is constantly changing and although many features like the EB's and GRS never really go away, they can change in size, color, appearance, and visibility. The SEB all but disappeared in small refractors a year or two ago, and I've seen richer colors than Jupiter has been presenting now. But basically, over the years through a 3" refractor I've seen moon and shadow transits, 6-8 zones and bands other than the NEB and SEB, some cloud detail in the SEB, NEB and EZ, and the GRS of course. It helps to boost your visual performance with a warming filter (I usually use an 85A or FL-D filter) and also with binoviewers. I've done a lot of observing over the years both mono- and bino- and I almost always pick out more detail through binoviewers. Jupiter is one of those targets you often have to really be patient with. BTW, if you can find it, you can see Jupiter in broad daylight through a 3" refractor.

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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6190357 - 11/12/13 10:43 AM

Quote:

Thomas have you seen a little bit orange in the Great Red Spot with your Vixen 80 or with your Zeiss 85 f/18?




Yes, but it's very pale, almost a very light brown. It doesn't stand out massively, as it does in a large telescope. Contrast on Jupiter in a small telescope is very slight and it takes great patience to see the details.

In a 30", it's like a painter's palette! So many different colors and hues.


Clear skies!
Thomas, Denmark


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6190399 - 11/12/13 11:01 AM

Quote:

Quote:

Thomas have you seen a little bit orange in the Great Red Spot with your Vixen 80 or with your Zeiss 85 f/18?




Yes, but it's very pale, almost a very light brown. It doesn't stand out massively, as it does in a large telescope. Contrast on Jupiter in a small telescope is very slight and it takes great patience to see the details.

In a 30", it's like a painter's palette! So many different colors and hues.


Clear skies!
Thomas, Denmark




Thank you Thomas,
I'll try it with my Vixen 80L the next time.

I had a similar experience last time I watched with my 4". I had the impression of a little light orange to light brown, too but I was not sure. The colour impression wasn't stable.
Only the little blue of the colour fringe around Jupiter was stable in the 4"
Clear skies,
Roland


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: PeterR280]
      #6190405 - 11/12/13 11:03 AM

Quote:

Has anyone noticed contrast variations based on seeing conditions? I recall a few months ago with very good seeing at 5AM, the bands were a much darker brown with a 4" than I am used to.



Hi Peter,
yes, I had a similar experience with my 4" f/11. With bad seeing the bands are just grey. What 4" do you use?
Cheers,
Roland


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

Loc: La Union, PI
Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6190424 - 11/12/13 11:13 AM

The GRS appears to have more saturation than last year. Other than the GRS and other main features, seeing color has a lot to do with time at the eyepeice IME. For me, seeing color began with recognizing white. Once you see whitye, then light grey and pale yellow becomes more distinct. On closer inspection, darker hues begin to resolve from the reddish hue of the EQ belts. I'm not sure what aperture makes the festoons easier to see as bluish, but if they show at all maybe color might be discerned.

The key seems to be Jupiter's colors are low contrast. Realizing that may help to begin seeing more color. Again, once you can discern white other colors stand out easier. At least for me, that was how I began to really see Jupiter in color. Once it happens to you, the amount of detail visible improves dramatically. Of course aperture helps, but so does actually learning to recognise color. If its elusive, keep at it. It will come. Try to find white and see whatever the aperture will deliver.

Edited by Asbytec (11/12/13 11:14 AM)


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ManuelJ
professor emeritus


Reged: 12/19/05

Loc: Madrid, Spain
Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6190646 - 11/12/13 12:56 PM

One thing that helps in seeing color is ruin your dark adaptation. I mean, shine a flashlight for some seconds.

You will be amazed how easy are Jupiter colors after that. And remember: low power!


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: ManuelJ]
      #6190673 - 11/12/13 01:09 PM

Hi Manuel,

this is probably what I experienced one time when I was sketching Jupiter with white LED.

Cheers,

Alexander


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PeterR280
Pooh-Bah
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Reged: 05/27/13

Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6191067 - 11/12/13 04:23 PM

I was testing the Celestron C102GT alongside an 80mm ED triplet. They both showed amazingly dark brown bands.

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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: PeterR280]
      #6191096 - 11/12/13 04:41 PM

Hello Peter,
you probably learned to see colors. That makes me hopeful.

The C102GT should be similar to my 102/1100 achromat. The triplet 80 ED has probably less CA than my Vixen 80L but the Vixen 80L has is quite good (with little CA), too. So I'll try to look at colours at the next observation and I'll try to use a flashlight to do some experimentes, too.

Clear skies,
Roland


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6191176 - 11/12/13 05:16 PM

I enjoyed the discussion on astrotreff.de, BTW. Your recollection of my observations of the Jovian moons with the 85/1600mm Zeiss is correct, but I can also see the size differences with my 80/1200 Vixen. In my 63mm Zeiss at 140x, or better at 210x, I can see that Ganymede is bigger than the other three and that Callisto is much dimmer at high magnification (meaning I can resolve its surface, but it gets so dim, my eye won't allow me to see a clear disk). Io and Europa appear identical in size and brightness in the 63mm, but their colors differ subtly, with Io being a very subtle reddish or yellow or even pink, while Europa is icy white. Ganymede is a beautiful golden yellow and Callisto dark brownish grey. All of this is much easier in my 150/1200 stopped down to 112mm and here the different moons have obvious size differences and colors. In this scope I can always identify them with 100% accuracy in good seeing, even without knowing their positions in advance.


Clear skies!
Thomas, Denmark

PS. Must travel to Sweden tomorrow, so can't continue the discussion until friday at the earliest.

Edited by Astrojensen (11/12/13 05:21 PM)


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youngamateur42
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Reged: 11/21/12

Loc: La Verne, CA
Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6191480 - 11/12/13 07:57 PM

To the Op:

The short answer is a lot. You can see a lot on Jupiter. On quick sessions I use my 70mm F/10 Achro and it still surprises me how good it is. I have regularly seen the Red Spot and many different dark areas light areas. Color if the bands is like a sort of light brown. One thing that tremendously helps is filtering. One of the best is 80A blue. Another is 15 or 12 yellow. I use these regularly, and they're pretty cheap to get I the Classifieds. I have often heard that a green is good too but I haven't used one before.


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PeterR280
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Reged: 05/27/13

Re: Jupiter in small refractor telescopes new [Re: youngamateur42]
      #6191555 - 11/12/13 08:39 PM

Niklo

I did not learn to see color. Most viewings, the bands are gray. This particular day when seeing was excellent, the bands appeared darker and I could see brown.


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UND_astrophysics
sage


Reged: 01/19/13

Re: Jupiter in small refractor telescopes new [Re: youngamateur42]
      #6191568 - 11/12/13 08:47 PM

Great thread guys! Some beautiful pictures!

Here is one of Jupiter I took through my smaller Vixen 70mm F/13 (AL-70 F refractor) and a cheapo webcam. Not as good as others here, but I thought I would post it.



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KJL
member
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Reged: 06/07/12

Loc: Boston, MA
Re: Jupiter in small refractor telescopes new [Re: UND_astrophysics]
      #6192076 - 11/13/13 06:02 AM

Quote:

Here is one of Jupiter I took through my smaller Vixen 70mm F/13 (AL-70 F refractor) and a cheapo webcam. Not as good as others here, but I thought I would post it.






This is what I usually see in my 80mm f/6 and 90mm f/7 triplets. I guess I need better skies, given the significantly better views higher up in this thread!


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: KJL]
      #6192095 - 11/13/13 06:50 AM

KJ, my experience is that with time spent behind eyepiece you will note many more features on Jupiter. Sketching helps enormously to gain more experience. Take for example my first Jupiter sketch (in fact from similar 80mm f/6 triplet as yours):

http://www-hep2.fzu.cz/~kupco/astro/2010/2010_09_16/pic/orig/Jupiter_20100916...


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: KJL]
      #6192118 - 11/13/13 07:22 AM

Quote:


This is what I usually see in my 80mm f/6 and 90mm f/7 triplets. I guess I need better skies, given the significantly better views higher up in this thread!




Hi KJL,
good seeing is important. I remember that looking with the Vixen 80L I saw some fine structures in the two main bands and the Great Red Spot. The problem was that the periods with good seeing were very short.
I think Alexander is right. Trying to do sketches helps to improve us to see and recognize more details. I love to make photos but I think both might be interesting drawing and then taking a video and afterwards try to compare the sketch with the photo.

Back to the seeing problem. Last summer I watched Saturn from my flat and the seeing was quite bad. So for about 20 minutes I wasn't able to see the Cassini division. Then suddenly I saw a black line between the A and B ring for a moment afterwards is was swimming again.
At a day with good seeing I saw the Cassini Division on end of June this year almost permanent. Then I took two photos
http://www.cloudynights.com/photopost/showphoto.php?photo=27768&password=...
and
http://www.cloudynights.com/photopost/showphoto.php?photo=27766&password=...

So both is important, good seeing and having learned to be patience and to see fine and weak details.

Clear skies,
Roland


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Ed Whitney
sage


Reged: 07/08/10

Loc: Palm Coast, Florida
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6192133 - 11/13/13 07:47 AM

Jupiter in an 8in EdgeHD and 8in newt only reveeled whites and pale greys. But, with an XT10i pale pinks and mauves were nice to see, but the red spot was still not really red. And the moons were discs, with Io definitely orange!

From this, I'm nearly certain you need large aperture to see colors in Jupiter.


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UND_astrophysics
sage


Reged: 01/19/13

Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6192140 - 11/13/13 07:53 AM

I found another Jupiter I did with my 70mm Vixen F/13. I am not sure why it is so small, I think it is because I did it much higher speed, but it has a bit more detail..Can even see a moon shadow..This was 35 frames per second max and stacked with registax. Not bad for a 70mm refractor. My Vixen AL70F and AL80F are my two favorite telescopes.





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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6192204 - 11/13/13 08:54 AM

Yesterday, I took out AS80/1200. I spent almost two hours observing Moon. Despite visible haze, the seeing was exceptional and I never saw such jaws dropping views in 80mm telescope before. Most of the time, I was using ATC 8E eyepiece (150x) and the image did not move at all!

At the end of the session I checked quickly Jupiter. It was still low with not the best seeing but I started to see some hints of equatorial festoons. I was paying particular attention to the colors. I was using CZJ O-10 (120x) and O-12.5 (96x) eyepieces. I noticed subtle differences in colors of Jupiter's moons (but I did not put down the details into my logbook). The Jupiter globe was of yellowish cast but bands were looking grey, may be, if would loose my imagination with a hint of dark brown.

Edited by Sasa (11/13/13 08:58 AM)


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UND_astrophysics
sage


Reged: 01/19/13

Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6192232 - 11/13/13 09:06 AM


I can see light tan colored bands visually through my 70mm, but then when I install a yellow filter I can see them even better. Seeing and atmosphere probably has a lot to do with it.


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6192308 - 11/13/13 09:46 AM

Hello Alexander,
that sounds good. So you saw a little bit of colour at the moons and the band with a little bit greyish to brown and you saw some hints of festoons. Did you draw a sketch?
Here in Bavaria near Munich the weather is currently cloudy and cold. Let's see if it gets better at the weekend.
Clear skies,
Roland


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6192320 - 11/13/13 09:54 AM

No sketch, sorry. Jupiter was still low and I was tired after 2 hours of looking at Moon. But I did sketch a small interesting region in Mare Cognitum.

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Glen A W
sage


Reged: 07/04/08

Loc: WEST VIRGINIA USA
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6192326 - 11/13/13 09:58 AM

Small refractors can work better on Jupiter than their small size suggests. I had fair results with a ch102hd. After I got a SW 100ED, my results improved a lot. The CA in the achromat really did hurt.

I looked at Jupiter for a long time before I could even make out the GRS. Today, I can see all sorts of detail. It's strange that practice would be so required just for seeing something that is already there.

I have never liked filters much. I don't feel like I can see anything more that way, and a small scope doesn't have much light to spare. GW


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: Glen A W]
      #6193087 - 11/13/13 05:15 PM

Glen, this was my case also. It took me more than half a year with my former 150mm f/5 Newton before I could detect GRS on Jupiter. Now I can see it in 63mm...

I'm no-filter man too. Main reason is that I'm lazy, already changing eyepieces is quite some hassle... But one day, I'm going to try them, just out of curiosity.

BTW, I was observing Jupiter again this night. I even started with sketching but within 4 minutes, the clouds were to thick and all could use in AS80 was just magnification of 96x. Anyway, here is my first quick and rough sketch, directly from the telescope. There was no point of making it looking better, after all I did not catch many features (I think GRS was just rising on eastern horizon, but I'm not 100% sure).



There was no point to check colors in those bad conditions tonight.


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UND_astrophysics
sage


Reged: 01/19/13

Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6193412 - 11/13/13 08:02 PM

Those pictures are turning out very nice! I have never tried sketching.

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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: UND_astrophysics]
      #6193838 - 11/14/13 12:45 AM

Quote:


I can see light tan colored bands visually through my 70mm, but then when I install a yellow filter I can see them even better. Seeing and atmosphere probably has a lot to do with it.



Your photo is nice. Do you see a little bit of orange in the Great Red Spot?


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6193842 - 11/14/13 12:49 AM

Hi Alexander,
thank you for your sketch. It's not bad (rather good) for such a short sketch although it's a pity that the clouds were coming so soon.
By the way is your moon sketch uploaded on your page?
Clear skies,
Roland


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6193940 - 11/14/13 03:13 AM

Roland, not yet. I'm using stippling technique for sketching Moon and it requires time. This is something to do during cloudy nights. And my last sketch of the Moon is the second one in the pipeline...

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

Loc: La Union, PI
Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6194036 - 11/14/13 07:03 AM Attachment (55 downloads)

Quote:

KJ, my experience is that with time spent behind eyepiece you will note many more features on Jupiter. Sketching helps enormously to gain more experience. Take for example my first Jupiter sketch (in fact from similar 80mm f/6 triplet as yours):

http://www-hep2.fzu.cz/~kupco/astro/2010/2010_09_16/pic/orig/Jupiter_20100916...




Truer words are rarely spoke, Alex. Someone mentioned seeing above, too. Both help get the most from observing Jupiter, including color. (My best in 8/10 seeing, it's not really a refractor but maybe it's a small one. )

Edited by Asbytec (11/14/13 07:08 AM)


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Sasa
professor emeritus


Reged: 11/03/10

Loc: Ricany, Czech Republic
Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6194058 - 11/14/13 07:24 AM

Amazing sketch Norme, is it coming from your 150mm MCT?

Edited by Sasa (11/14/13 07:24 AM)


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UND_astrophysics
sage


Reged: 01/19/13

Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6194067 - 11/14/13 07:35 AM

Quote:

Quote:

KJ, my experience is that with time spent behind eyepiece you will note many more features on Jupiter. Sketching helps enormously to gain more experience. Take for example my first Jupiter sketch (in fact from similar 80mm f/6 triplet as yours):

http://www-hep2.fzu.cz/~kupco/astro/2010/2010_09_16/pic/orig/Jupiter_20100916...




Truer words are rarely spoke, Alex. Someone mentioned seeing above, too. Both help get the most from observing Jupiter, including color. (My best in 8/10 seeing, it's not really a refractor but maybe it's a small one. )




Wow That is very nice! Good Job!


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Niklo
sage


Reged: 03/29/13

Loc: Bavaria
Re: Jupiter in small refractor telescopes new [Re: UND_astrophysics]
      #6194194 - 11/14/13 09:27 AM

Quote:


Wow That is very nice! Good Job!



Yes, indeed, that is a very nice sketch with many details! Congratulations!
Clear skies,
Roland


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

Loc: La Union, PI
Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6194276 - 11/14/13 10:21 AM

Quote:

Amazing sketch Norme, is it coming from your 150mm MCT?




Yes, now you know why I love this keeper.

I posted it (the best to date, of course) to show what might be seen in a slightly smaller aperture refractor and to support the color argument above (this was shortly after color became apparent, that took a good while observing to learn to recognize it.) Also to support your assertion time at the eyepiece, and time with the subject, is important - a month or two of almost nightly observation.

The whites near the base of the festoons are not terribly difficult, but once the white streak just along the SEB northern border broke, it was game on. All of a sudden, if that streak was white, then the rest of the EZ had to be a different color. Then the NTrZ was not white, it was pale yellow. The STrZ also became two toned, white and light grey. Light grey was more obvious once white was recognized (outside that at the base of the festoon.)

The NTeZ was indeed not white, either, it was light grey. Then further observation showed darker hues along the edges of the SEB and indeed the SEB was not the same hue all the way around. The faintest and most difficult contrast were the lighter patches along the northern NEB. So, instead of two belts and a red spot, Jupiter just exploded to life. It was an incredible experience.

It seems to wear off, though. Not having observed Jupiter in over a year, recently the views have been flat, almost grey scale. But, surely it will come back with time.

In good seeing without collimation or thermal issues, both well known qualities of refractors along with very good low contrast transfer, you can see quite a lot when you spend the time. That /could/ be about the level of bright low contrast detail visible, not unlike your own sketches, Alex, in something near a 4" refractor.

Et al, thank you. It's been a real pleasure using a smaller aperture. Once color becomes apparent, once we learn to recognize it, the level of detail improves dramatically. When conditions permit it's literally - look up and say a silent prayer of thanks - stunning.

(Color was applied using sketch paint, a freeware paint program. Try it. They are more saturated in the sketch so the viewer does not have to struggle to see them. Jupiter is, indeed, almost grey scale. Seeing that 'almost' difference is what takes some training.)

Oh, and again to repeat what Alex said, work on Jupiter and by all means sketch it. It really does help to see more, to capture every detail the aperture can put up. Alex is right about that, IMO, as can be shown in his work above.

Edited by Asbytec (11/14/13 11:02 AM)


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jag767
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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6194282 - 11/14/13 10:28 AM

There's been nights where the level of color/detail I can see in Jupiter with my 65mm completely amazes me. Same can be said of the detail in larger dso's and the unbelievable widefield view for such a small instrument. Mine is always ready to go, and sometimes the challenge to see what can be seen can be quite enjoyable.

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Re: Jupiter in small refractor telescopes new [Re: jag767]
      #6194302 - 11/14/13 10:40 AM

No doubt, it can be amazing and enjoyable, as you say. Which is why we do it.

On color...
http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Board=Sketching...


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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6194318 - 11/14/13 10:49 AM

The most important thing in planetary observing is in fact your sky, not your instrument. I have had this proven to me time and again. The scopes I have seen the most with were cheap ones I could drag out the door in one piece and actually use. I saw as many galaxies with my first 60mm as with any scope since, believe it or not. On planets, catching that rare good seeing means being out there a lot. I have, four or five times, caught that period of steady air, and it's amazing once you have it happen to realize how much can be seen. GW

Edited by Glen A W (11/14/13 10:50 AM)


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Re: Jupiter in small refractor telescopes new [Re: Glen A W]
      #6194340 - 11/14/13 11:05 AM

Glen, just to reinforce your comment, I believe you are absolutely correct. Retiring to the tropics with steady air really allows one to get into Jupiter. Absolutely. (Along with cooling, collimation, etc., of course.) It all matters: seeing, baffling, all of it contributing it's share, with seeing perhaps being the biggest part. Yep, when conditions permit and everything else is together, it's on...

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Re: Jupiter in small refractor telescopes new [Re: Glen A W]
      #6195910 - 11/15/13 03:39 AM

I once did a bit of a study as to what is the best image I could aspire to of Saturn, Jupiter and Mars if the seeing were perfectly steady, the optics perfect and my imaging was limited only by diffraction effects. My results for Jupiter, 3" aperture to 18"


NB the above is just a teaser to get you to click on. You need to see the full size image, here.
What I found amazing is how often the best imagers on CN approach the diffraction limit, at least for up to 11", or much more rarely, 14" apertures. It's also quite remarkable how much detail one can coax out of a 4". Seeing is of course much less of an issue with smaller apertures than with those over 10". Sort of falls in line with the old adage that 300x is about the upper limit of useful magnification no matter what the aperture size is. Except of course for those with ageing vision where 600x on a steady night may be quite welcome on a C14! Like for yours truly


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Re: Jupiter in small refractor telescopes new [Re: Samir Kharusi]
      #6195961 - 11/15/13 05:25 AM

Very interesting thread!
Hope you don't mind- I saved your picture for later reference???
----
The 3" image reminds me of what I actually see around my observation site with a 6" on account of atmospheric effects.
M.


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6195967 - 11/15/13 05:38 AM

Samir, nice homepage!
FYI, I have bagged Encke with an excellent 8" and Olympus Mons with an excellent 6". Your images seem to back these observations
-ONLY- if atmosphere cooperates! (not often enough!)
M.


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UND_astrophysics
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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6197167 - 11/15/13 08:49 PM


Wow, There is some real talent here. Nice work!


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6211974 - 11/23/13 06:42 PM

Hi,
at the moment the weather is still bad. I had no chance to watch Jupiter but I found two nice videos of a 3" f/16.
It even shows the orange colour in the videos:
https://www.youtube.com/watch?v=ZOsjLh0h5Oc
and
https://www.youtube.com/watch?v=ZZBL6Ex1Vu8
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Samir Kharusi]
      #6211980 - 11/23/13 06:46 PM

Hi Samir,
that's an interesting picture to compare the telescopes views
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6236603 - 12/06/13 03:50 AM

Hello,
now I was able to watch Jupiter and take a new Jupiter video with my Vixen 80L at December the 3rd 2013 at about 12:44 AM German time. I used a diagonal mirror. After stacking and sharpening the colour changed a little bit. So I want to show a little sharped picture that shows the greyish bands with a touch red and brown, the light orange of the Great Red Spot and a grey with a touch blue in the festons. The first pricture is just an attempt to show the colours close to the colours in the eye piece. The view in the eyepiece was different and some contrasts ... were better.

With more sharpening the contrast got better but the colours shift a little bit too much:

And a two times magnified version:


Clear skies,
Roland

Edited by Niklo (12/06/13 04:03 AM)


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6236674 - 12/06/13 06:08 AM

That is very, very nice!


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6236772 - 12/06/13 08:05 AM

Nice images Roland. I'm probably color blind, but I do not see colors on Jupiter nowhere near to your first image. I was observing Jupiter couple of days ago, this time through ED100

http://www-hep2.fzu.cz/~kupco/astro/2013/2013_12_02/pic/orig/Jupiter_20131202...

but I saw basically no color in main belts.


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6236778 - 12/06/13 08:08 AM

Pretty amazing what a smaller scope can show!
M.


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6236820 - 12/06/13 08:41 AM

Great editing Roland. You can restore the colors in Photoshop or Lightroom, although my eyes don't see the loss you are referring to. Perhaps it didn't translate through the web compression.

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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6236856 - 12/06/13 09:01 AM

Thank you very much Thomas. I'm happy that you like the photos.
Clear Skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6236900 - 12/06/13 09:22 AM

Great shots, Roland!!

Cheers,
Bill

Edited by Bill Friend (12/06/13 12:22 PM)


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6236902 - 12/06/13 09:24 AM

Hi Alexander,
the first picture is with reduced sharpening and reduced colours to make it close to the view in the eye piece.
Your telescopes are larger and better but are the colours similar in your telescopes?
The colours are weak but I can see them a little bit. I saw light orange in the Great Red Spot as well in the eye piece and on the photos. The greyish main belts have a little brown and reddish hint in them and the festons are more grey with a hint of blue.
I think that a good seeing is necessary to see the colours otherwise the belts are rather grey.
Your sketch is very nice. You see so many details just the colours hide somehow even in the picture. That's a pity. OK maybe it depends on the monitor to see the colours in my pictures.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Bill Friend]
      #6236907 - 12/06/13 09:26 AM

Bravo Roland! Nice shots with an 80mm!!!

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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6236909 - 12/06/13 09:27 AM

Quote:

Pretty amazing what a smaller scope can show!
M.



Thank you, you are right. I was amazed again too to see so many detals in the 80/1200 refractor.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6237484 - 12/06/13 02:07 PM

I highly recommend using a Baader Semi-APO filter with Jupiter. The colors and detail really "pop" with this filter and are very natural in appearance.

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Re: Jupiter in small refractor telescopes new [Re: Jon_Doh]
      #6237694 - 12/06/13 04:17 PM

Hi Jon,
thank you for your compliment. I don't have Photoshop but it's no problem

Hi Bill and Jim,
thank you very muc for your nice comments.
Cheers,
Roland


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Re: Jupiter in small refractor telescopes new [Re: bykhed]
      #6237711 - 12/06/13 04:25 PM

Quote:

I highly recommend using a Baader Semi-APO filter with Jupiter. The colors and detail really "pop" with this filter and are very natural in appearance.




Hi,
thank you for your advice. Even if the pictures do not look good enough but the Vixen 80L (80/1200) is almost a semi apo with very little CA. Playing with the colour in the pictures show some CA but it does not bother me.

I think that the Semi APO will dim the view too much and does not improve the contrast much in a 80 f/15 but I'll test it in the 102/1100 refractor.

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6237740 - 12/06/13 04:47 PM

Quote:

I think that the Semi APO will dim the view too much and does not improve the contrast much in a 80 f/15




That would be my concern as well. With these small scopes, light is precious, and always in short supply. And false color is a non-issue anyway.

BTW, I had a chance to try a 80mm f/15 Jaegers lens at a star party in September, and that was a REALLY sharp and color-free 80mm f/15. Going from memory, it was clearly better corrected for color than my Vixen 80L. It fell short of the 85mm f/19 Zeiss A, though, but then again, what doesn't?


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6237768 - 12/06/13 05:14 PM

Hello Thomas,
so the Jaegers was even better than the Vixen 80L. Sounds interesting. Maybe they used some special glass like the Zeiss AS 80/1200 does?

I heared about the Jaegers lenses but although the name sounds German I don't know anybody in Germany who owns a Jaegers refractor.

Even if my Vixen 80L might not be the perfect my Vixen 80L is quite good for me.

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6237862 - 12/06/13 06:14 PM

I've been very happy with my 80L as well. I've got many fond memories with it under the stars. I've done some crazy things with it. It is a phenomenally good double star scope. It does show some spherical aberration, though. Perhaps yours is better corrected? It's possible.

I don't think the Jaegers use special glass, it was just done right. They are pretty rare outside the US and Canada, I think.


Clear skies!
Thomas, Denmark


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james7ca
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6238413 - 12/07/13 01:00 AM Attachment (82 downloads)

Here is a shot of Jupiter I did a few years ago using afocal/eyepiece projection with an Astro Tech AT72ED (72mm aperture f/6 prime, working at an effective focal length of 1036mm). This was created from a simple stack of six still images (Photoshop) that were taken with a Nikon DSLR, not a video conversion using something like Registax (which should produce even better results).

You can just make out the Great Red Spot on the lower right of the planet. The moons were captured with the same exposures, but were brightened a bit in post processing.


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Re: Jupiter in small refractor telescopes new [Re: james7ca]
      #6238438 - 12/07/13 01:44 AM

Hi James,
for stacking just six images the result is quite good. Could you do a video with more images? Then you could use Registax or something similar and the result will be much better. I have not tried to stack 6 images but it's probably similar to a single frame image and that depends on the seeing. For my picture I used a video with 500 frames but I think even 100 or 200 frames will do a quite good job.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6238456 - 12/07/13 02:10 AM Attachment (47 downloads)

Quote:

Nice images Roland. I'm probably color blind, but I do not see colors on Jupiter nowhere near to your first image. I was observing Jupiter couple of days ago, this time through ED100

http://www-hep2.fzu.cz/~kupco/astro/2013/2013_12_02/pic/orig/Jupiter_20131202...

but I saw basically no color in main belts.




Roland has some terrific captures with his 80mm scope, really first rate work You were talking about color and not seeing much visually, and the fact is the less aperture you have the less saturated the color will be...especially visually. While the camera has the advantage of lengthy integration time, building up data with hundreds or thousands of frames, the way to better color is through aperture. I love shooting with my 100ED and TEC 140 refractors, but the side-by-side comparison below shows the considerable gap between the smaller refractors and the bigger C11 Edge HD. There is plenty of detail in both refractor pix, and decent color, but more aperture will put you in a different league altogether when it comes to resolution and color saturation

Clear Skies,
Brian


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Re: Jupiter in small refractor telescopes new [Re: BKBrown]
      #6238510 - 12/07/13 04:53 AM

Wow Brian, your images are great. There are much more details visible in your pictures and the colours of the SW100 ED is really APO like. You probably had a first class seeing with very good telescopes.
How are the colours visible in the eye piece of your SW 100 ED? What SW 100 ED do you have? Do you have the Evostar 100 ED
http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3684_E...
or the Equinox 100 ED
http://www.teleskop-express.de/shop/product_info.php/info/p1068_Skywatcher-Eq...
I'm happy to have nice views of Jupiter and see a little bit colour and cloud structures with the Vixen 80L but even the ED 100 is really much better. Maybe you could describe a little bit what you see visible in the ED 100, in the TEC 140 and in the C11 (almost Hubble Space like pictures . By the way the photographic gab between 140 and C11 is not so big as I expected. Of course the C11 is better but even the 140 and the 100 show great pictures.
Clear skies,
Roland

Edited by Niklo (12/07/13 07:03 AM)


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6238560 - 12/07/13 06:32 AM

Quote:

Hi James,
for stacking just six images the result is quite good. Could you do a video with more images? Then you could use Registax or something similar and the result will be much better. I have not tried to stack 6 images but it's probably similar to a single frame image and that depends on the seeing. For my picture I used a video with 500 frames but I think even 100 or 200 frames will do a quite good job.
Clear skies,
Roland



I generally don't use my AT72ED for high-resolution work (at least not any longer). I've got larger instruments now and I use a video camera for my planetary work. If I have time I might go back and put that camera on the AT72ED just to see how it compares to the 5" and 6" telescopes I now use. However, I so seldom have clear and usable nights that I'm not sure that I'd want to spend too much time with the AT72ED (at least for astrophotography, the AT72ED is still a great grab-and-go scope for visual work).


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6239073 - 12/07/13 01:15 PM

Hi Thomas,
I don't if my 80L is better corrected. I would expect that they are quite the same. How do you see the spherical aberration and how can it be avoided? Is an aplanat needed to avoid the spherical aberration? f/15 should help a little bit against the spherical aberration, shouldn't it?

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: james7ca]
      #6239074 - 12/07/13 01:16 PM

Hi James,
yes, it would be interesting to see a comparison between different telescopes. A web cam should be fine to do planetary videos.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6239157 - 12/07/13 01:56 PM

Quote:

How do you see the spherical aberration and how can it be avoided?




The spherical aberration is visible in the star test, as the fresnel patterns aren't identical on either side of focus. The first diffraction ring is a bit more prominent than it should be, as well. But it isn't a major disaster. The lens performs fine, it's more a eyeopener of just how sensitive the star test is, really.

So, why does my lens have it? It has nothing to do with the design, just with how it's made, IE one or more surfaces are slightly more or less curved, than the design calls for. Yours may indeed be perfect.

It may be a slight turned down edge, because when I stop the lens down to a 60mm f/20, the star test is completely perfect. I haven't experimented with various stops to see, where the cutoff lies. Maybe I can get up to 70mm? 65mm? I don't know. I just made a 60mm mask, since I wanted to test how such a scope performed, after reading about one, that was supposed to be nothing short of spectacular. And it was correct. A 60mm f/20 with a perfect lens can do insane things. It outperforms my Zeiss Telemator on lunar/planetary.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6239329 - 12/07/13 03:33 PM

Hi Thomas,
thank you for the explanation. I haven't tested that. Maybe it's better maybe it's worse. I'm just happy how it is. There will always be a better and a worse
Interesting is that the inner 60 mm are very good. Maybe that's a general problem...
Maybe I'll try to stop the Vixen down to 50 mm to make an apo like achromat...
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6239729 - 12/07/13 07:20 PM

Hi Roland

I've just come in from a several hour long Jupiter session with my 85mm f/19 Zeiss apochromat. The seeing was very good. I was using a Baader Maxbright binoviewer and 1.65x GPC glasspath corrector, giving 105x with my 25mm Zeiss microscope eyepieces. The view was superb. I could essentially see all the details in your photos. The one in the middle is the closest and is really impressively close to show perfectly what I could see tonight. It really was that sharp, albeit with somewhat more subtle colors, apart from the NEB, which was very dark, chestnut brown. GRS rotated into view, and was quite inconspicuous at first, but once near the meridian, it became very well visible, though it was not as clearly colored as in your pictures. It was more of a pale brownish-red hue. Interestingly, the SEB was not split on the half that is on the other side of the planet, as seen from GRS, but the color was much deeper and as a whole, SEB was much more prominent on the "boring" side. The GRS side shows much more detail. The equatorial zone showed a large festoon, just at the beginning of the observation, around 9.15 PM (21.15), but it soon rotated out of view. It was quite difficult to see. I also had the good luck to watch an Io shadow transit in its entirety. It was VERY clearly visible all the time, though Io itself remained invisible.

It is several years since I observed Jupiter last time with the 85mm, if my memory doesn't fail me, and I've never observed it with the 25mm Zeiss microscope eyepieces in the bino on this telescope. I was frankly stunned by how good the views were and how many details I could so readily see. I also tried higher magnifications, 166x with a 2.6x GPC, but the image became too dim, although there were hints of even more detail than at 105x, but my eyes needed the brightness. When I was younger, I had no trouble observing Jupiter with higher magnifications, but those days seem to be over...

I also tried a 9mm ES100 eyepiece, just for fun, and the view was very, very good! A bit too much magnification, but lots of details visible. The view with the bino was much, much better, though. With the bino, contrast goes through the roof, although you can't use as much magnification, because the view gets too dim, if you try to use the same magnifications you would usually use with a single eyepiece.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6240069 - 12/07/13 11:48 PM Attachment (32 downloads)

Quote:

Wow Brian, your images are great. There are much more details visible in your pictures and the colours of the SW100 ED is really APO like. You probably had a first class seeing with very good telescopes.
How are the colours visible in the eye piece of your SW 100 ED? What SW 100 ED do you have? Do you have the Evostar 100 ED
http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3684_E...
or the Equinox 100 ED
http://www.teleskop-express.de/shop/product_info.php/info/p1068_Skywatcher-Eq...
I'm happy to have nice views of Jupiter and see a little bit colour and cloud structures with the Vixen 80L but even the ED 100 is really much better. Maybe you could describe a little bit what you see visible in the ED 100, in the TEC 140 and in the C11 (almost Hubble Space like pictures . By the way the photographic gab between 140 and C11 is not so big as I expected. Of course the C11 is better but even the 140 and the 100 show great pictures.
Clear skies,
Roland




Thanks Roland I did have very good seeing for all of those images, I believe you can get good pictures regardless of what scope you use, it just takes some practice and patience. My visual views in the TEC are similar to what you see in the SW100ED image, only sharper. Both refractors tend to appear reddish to me with cooler tone polar areas; the belts and zones stand out clearly. I can often make out the GRS area and its wake turbulence, also patchy highlights in the Equatorial Zone. The C11 can show me finer highlights and a larger range of color, but nothing like the deep saturation in the image...there are limits Like you, I am surprised at how well the TEC, and even the SW100ED, can hang in there and bring home the details. But the C11 is clearly in another league altogether for resolution and color.
The image below is my planetary imaging set up when I am serious about using the refractors, the TEC and SW100ED can stay mounted for several weeks like this during a "small bore" imaging campaign. A WO ZS66SD or AT65EDQ often ride atop my Skywatcher (which is the US version of the Evostar I believe)...

Clear Skies,
Brian


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Re: Jupiter in small refractor telescopes new [Re: BKBrown]
      #6240705 - 12/08/13 12:23 PM Attachment (57 downloads)

This is such a telling set of images.

In a recent forum on Strehl, I posted a "Simulation" and I marked several details as to how they would appear in a 6" f/15 acrhomat, and at what point detail would fall below the resolution of that instrument.

If one looks at the festoon with the long tail, it is a classic example of diffraction at work.

In the 11" scope, the tail is long and consicious. It starts wit 20% or so contrast.

And in my writup on Strehl, I has suggested that this kind of freature, and ovals on Jupiter, would be difficult targets for a 6" achromat because of the loss of contrast transfer from CA and the contrast loss of the apeture itself.

I even suggested that some of these features would be difficult in a 6" APO (and I know that to be the case from my own observing experience.

And your pictures demonstrate exactly. This kind of thin, low contrast detail as shown in this long arc coming sweeping down and across is being lost completely in the 4" scope, and only hinted at in the 140mm, but clear and well extened in the larger scope.

Here is my simulation. And again, this is only a simulation, but notice how close I camse.

The black lines are about 1.5 arc seconds in length. I had suggested that the diffraction and CA in a 6" f/15 achromat would make the details that are next to them in the simulataion below the scopes contrast transfer ability.

And here we are.. Pictures that cleary show the contrast being reduced for these same kinds of features.

I just used MTF to calculate the 1.5 arc second size as being the point where th eobserver would no longer be able to detect detail at 6" with chromatic aberration, even if the apeture were otherwise perfect.

So, here is the simulation, and you pictures seem to match very well with how the simulation suggested a 6" achromat would do. Your scope is 5.5", but the polychromatic Strehl is probably on the order of .95 to .97, while in the 6" f/15 acromat, the polychromatic strehl is only about .75, though the photopic strehl (green light) is above .90

Anyway, anyone going back and forth with the simulation I did and the pictures you took I think might be surprised at how close the simulation came.

That kind of tail is difficult even in a 6" APO, and for a 6" f/15 achromat is out of reach.

Not for a C11 though, and once again, having owned one of those and compared to a 6" refractor, my result was in line with your pictures.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6240712 - 12/08/13 12:26 PM

And by the way, I posted this picture last week.. It is availeble in the thread on Strehl on the Equipment Forum.

I give myself an "A +"


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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6240750 - 12/08/13 12:46 PM

Brian's picture and my post just above this go back to our my remarks on your "Ovals' captured in your drawing on the Solar System Forum.

Brians pictures capature this really well.

Norme, let me assure you that I have the very highest regard for your planetary obesrvation skills. Based on our numerous dialogs on various forums and our on comparisons on observations on Ganymede and Io, and other challanging targets, I know you to be one of the best planetary observers out there. You have my complete and utter respect.

So, this is just a clinical comment. Please don't take it any other way but as an extension on our ongoing dialog about contrast transfer.

Brians pictures show exactly what I was talking about. In the eddy structure following the GRS, one can see that while some of this structure is within the angular resolution capabilities of even the 140 TEC, the contrast transfer of the smaller apture reduces their ability to show low contrast detail smaller than about 1.5 arc seconds.

For you at 6", this meant that this turbulent area behind GRS has a smooth, ovalish appearance.

And even in the TEC 140 pitcture that brian took, the eddy structure is hinted at, but not clearly defined. in-flow of the Eddy is a bit smaller than 1.5 arc seconds, and would be difficult at 6" (Refractor or reflector, does not matter) because the contrast transfer for these smaller aptures simply gets to low to really see.

But the 11" apeture has almost twice the contrast trasfer for a detail that is 1.5 arc seconds wide than a 140mm apeture would have.

And this is why I said that what appeared as ovals in your scope (or even in my 6" APO) are far more defined as in-flow in an eddy structure in a larger speture.

Brians pictures show this almost perfectly.

Using the 1.5 arc second long lines in my simulation, one can indeed see that very low contrast detail that is smaller than this is almost impossible to see in the 4" and 5.5" apeture, but detail down to about .75 arc seconds (the long, thin tail of that festoon) are still showing in the C11.

Classic stuff. Exactly in line with MTF.

For a given telescope, I can use MTF to very accuratly predict how it would compare to another telescope.

And I did...

And here Brian has provided a great example that was pretty much in agreement with my prediction.

Hmmmmmm.


I know. People dismiss it as book stuff and just "Theory". Not real world.

Really? Seems to me that the book stuff got this one right.

You I know, have become more of a believer though, and the more our dialog progresses, the more I think you are far more in tune with MTF than most forum members, and you must know that I deeply enjoy or converstaions on the subject.

One day we have to re-visit the dialog between "Detecting" a detail and "Resolving" a detail..


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6240792 - 12/08/13 01:10 PM

Hello Eddie,
the 3 pictures in the 3 telescopes have not been at the same day. So the festoons are different.
Please look the dark line below the great red spot. It's longer in the 140 TEC than in the C11. So either the TEC is better (probably not) or it's taken on a different day.
So the festoon comparison does not work, too but you are probably right that a C11 can show finer details then a 140 mm APO/ED if the seeing is perfect. The strange thing is that the 140 mm refractor shows very much details and that the difference to the C11 is not so big as I expected.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: BKBrown]
      #6240807 - 12/08/13 01:16 PM

Hi Brian,
thank you very much. So you see colours in your ED 100. How would you describe the colour of the Great Red Spot in the ED 100 and the colour of the bands?
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6240887 - 12/08/13 01:45 PM

Hi Thomas,
thank you for your nice and interesting report. The bino view sounds interesting. Have you tried it at the Vixen 80L, too? If you look without bino view and go up to 160x it should be bright enough, shouldn't it? And you see more details in 105x with the bino view than in 130x or 160x without bino?


Quote:


The one in the middle is the closest and is really impressively close to show perfectly what I could see tonight.




Which one do you mean? The festoon or the wake turbulence near the Great Red Spot?

Quote:


I also had the good luck to watch an Io shadow transit in its entirety. It was VERY clearly visible all the time, though Io itself remained invisible.




You had really luck to be out at the right time.
To see Io before Jupiter is really hard that would have been too much luck.

I wish you clear sky and nice observations (maybe with your Vixen 80L?),
Roland


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6240890 - 12/08/13 01:49 PM

Glad to help support your often frustrating campaign to educate folks on MTF I'm already a believer; feel free to use the 3-way side-by-side anytime you like Eddgie...

Clear Skies,
Brian


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6240900 - 12/08/13 01:54 PM

Quote:

Hello Eddie,
the 3 pictures in the 3 telescopes have not been at the same day. So the festoons are different.
Please look the dark line below the great red spot. It's longer in the 140 TEC than in the C11. So either the TEC is better (probably not) or it's taken on a different day.
So the festoon comparison does not work, too but you are probably right that a C11 can show finer details then a 140 mm APO/ED if the seeing is perfect. The strange thing is that the 140 mm refractor shows very much details and that the difference to the C11 is not so big as I expected.
Clear skies,
Roland




The images were not taken on the same day, but over a roughly ten day period. That particular festoon manifested for rather a long time during the last apparition Roland, so I am not so sure it is not a good example.

Clear Skies,
Brian


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Re: Jupiter in small refractor telescopes new [Re: BKBrown]
      #6240962 - 12/08/13 02:43 PM

Hi Brian,
it's not clear if the festoon was exact the same size during the whole 10 days so... but everybody knows that an 11" telescope is able to show more details than a 5,5 " telescope. So the 11 shows the festoons better.
I want to come back to the "Jupiter in small refractor telescopes". So I would be happy to read more about this not not about Jupiter in large reflector telescopes

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6240975 - 12/08/13 02:53 PM

Hi Roland

Quote:

The bino view sounds interesting. Have you tried it at the Vixen 80L, too? If you look without bino view and go up to 160x it should be bright enough, shouldn't it? And you see more details in 105x with the bino view than in 130x or 160x without bino?




With the bino, contrast is increased a lot. I can see details with much more certainty, even if I can't use the same magnification as with a single eyepiece. 100x with the bino shows the image about as large and as detailed, but with much more certainty, as the view with a single eyepiece at about 140x, somewhat depending on the object.

I haven't done much bino observing with the Vixen 80L, because it can't reach focus without a glasspath corrector, which means I can't use lower magnifications on it. If I want to use the binoviewer without barlow, I have to use it straight through or buy a shorter focuser. The 85mm Zeiss has lots and lots of back focus and can use binoviewer without barlow.

In this case, I could have used the 80L with the binoviewer and the 1.65x GPC and reached focus, but I didn't have my 80L with me, since I observed from my parent's place and my 80L was left at home. I will try to set the two scopes up side by side sometimes and do a binoviewed shootout. Jupiter will remain high in the sky for several months, so there's plenty of time for experiments. And I do happen to love doing these side-by-side shootouts.

Quote:

Which one do you mean?




I meant the photo, the middle one, with Jupiter flanked by his moons, where the contrast was enhanced. That shows almost exactly how I saw Jupiter in the 85mm.

Quote:

I wish you clear sky and nice observations (maybe with your Vixen 80L?)




Maybe I'll get the 80L out next time! But the 85mm comes first, if I have to choose. It has a special place in my heart.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6241016 - 12/08/13 03:16 PM

Hi Thomas,
I'm close before buying a bino view
It's a pity that the Vixen 80L does not have enough backfocus. The Vixen has much backfocus but probably not enough to use a diagonal. The original focuser is very long so it would work as a baffle wouldn't it? Is that the problem with the Vixen focuser?

Quote:


I meant the photo, the middle one, with Jupiter flanked by his moons, where the contrast was enhanced. That shows almost exactly how I saw Jupiter in the 85mm.




Yes, that's a pretty good view.

Quote:


I will try to set the two scopes up side by side sometimes and do a binoviewed shootout.




That would be really interesting. Of course the Zeiss will show a better view with no CA, more contrast.. but the view in the Vixen is quite good, too.

Quote:


Maybe I'll get the 80L out next time! But the 85mm comes first, if I have to choose. It has a special place in my heart.




I really can understand you.

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6241066 - 12/08/13 03:59 PM

Quote:

The original focuser is very long so it would work as a baffle wouldn't it? Is that the problem with the Vixen focuser?




No, not at all. The problem is just that it can't be racked inwards enough to reach focus with the binoviewer without a GPC. I need about 4cm inwards travel, to reach focus with all eyepieces without barlow/GPC. The focuser is solid and smooth, no problems here either.

If you're just interested in high magnification views, the original focuser will do fine with a binoviewer. A binoviewer is definitely worth it for lunar/planetary views. Solar views are truly excellent as well. It can get very addictive.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6241220 - 12/08/13 05:39 PM

With 110mm, I see mostly shades of gray. The GRS has a very faint peach color with a hint of a umber in the nucleus of the swirl , and the SEB shows the slightest suggestion of a light salmon tinting. but only at its widest parts around the GRS. These tintings are for me, very subtle. The peach is the most pronounced, but even here it is hard to see it as much more than "not gray."

In larger apertures, I see far more color, but at 110mm, this is about the only color I personally see.

Be aware that people have much different color sensitiveness and many men are partially color blind for some making subtle shadings hard to see.

Also, magnification plays a factor. At 200x, Jupiter itself is slightly bigger than the Foveola of the eye, which is where the color receptors in the eye are densest. The Foveola is only about .35mm in size. Past this and it is a mixture of rods and cones, tapering to only rods further out. Because the density of cones outside of the Foveola is so low, it takes a lot more light to get the same color perception as when the target detail Is exactly centered over the Foveola.

For this reason, using a smaller aperture at more than about 200x really cuts the chances of seeing any color at all because of the very small exit pupil and the fact that more of the planet is falling outside the diameter of the Foveola. It makes it hard to see color except at the very point where your gaze is directed. In a small aperture it is hard to see the entire disk in color at the same time.

For larger apetures (12" and more") there is enough brigness that even at 300x, the entire disk will show color.

But for small instruments, best to keep the power to about 150x or less so that the light is as concentrated into the Foveola as possible if you want to see how much color you can get out of Jupiter.

Someone using a telescope at 200x would perhaps only have a chance of spotting color at more towards the center of the disk. Best chance of seeing the most color in a small scope is when the image is a bit smaller so that it fits entirely over the Foveola.

Over 200x though, as you move your point of interest over the disk and concentrate on a singe point on the disk, usually you can eek out a bit of color. GRS should be visible with pale color at 120x.

One other feature has shown color to me. Last time Jupiter came around, I saw a very distinct brown barge at high power in a 100ED f/9. The color was not well saturated, but enough that I saw it as being brown.

But that is what I see in the 110mm at powers between about 120x and 150x.

Hope this helps.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6241867 - 12/09/13 12:08 AM

Hi Ed,

I certainly agree that when it comes to telescope performance the MTF tells most of the story. But it doesn't tell the whole story, and one needs to be pretty careful when referring to webcam images in support of the MTF's impact on visual observing.

Firstly, because when comparing Brian's (beautiful) images from the C11, TEC140, and SW100ED posted earlier, all those images have almost certainly been processed in ways that artificially boost the contrast at various spatial frequencies (e.g. with wavelets). That said, the processing here seems to have been done really nicely - Jupiter looks realistic and the colours and contrast in the TEC140 image in particular closely resemble what I see in the eyepiece with that telescope. Because of the relatively light touch used, I suspect the effect is somewhat similar to boosting the contrast at each frequency to its theoretical maximum with an unobstructed pupil, which means a bigger boost in the C11 image relative to the others. In any case, my point is that unless you're somehow rolling back the effects of this filtering, I don't think one can make fair comparisons about the contrast of features relative to the predictions of the MTF on the basis of images that have been processed to defeat the contrast diminution brought on as a result of the impact of the obstructed pupil on the MTF. (A comparison based on raw frames or even straight-up stacks would be fine, provided they're not hit with wavelets or other non-linear filtering).

Secondly, when it comes to visual use, the eye-brain combination does some pretty funky non-linear filtering of its own. So MTF comparisons need to account for the visual response of the eye-brain system too. For example, you're a fan of binoviewing, I think? The reason binoviewers are effective is because they cause additional eye-brain filtering to kick in. This boosts apparent contrast, but the MTF of the optical system is unchanged. So if the MTF were all you needed to know to describe the visual planetary performance of a telescope, then a binoviewer would not lead to any improvement. To put it another way, if you stuck a pair of perfect CCDs at both eyepiece ports of an optically perfect binoviewer and added the resulting images you'd have the same image as without the binoviewer. Assuming no light loss and a noise-free detector, the digital image would be the same in terms of signal-to-noise as a single detector used without the binoviewer. The pupil is untouched, so the optical transfer function and MTF are the same in both cases. But visually, you'd probably enjoy a better view with the binoviewer. I think most people find (certainly I do) that binoviewing planets makes for an improvement in contrast (also in the visibility of colour). So something other than the MTF is at play here.

Bottom line: the MTF is a really good guide for selecting the right telescope for a given purpose. But post-processing of webcam images can improve the contrast in a system with a poor MTF, and visual observing requires consideration of the non-linear filtering of the eye-brain system, which can also improve contrast. And an additional consideration (which I'm ignoring) is the impact of the atmosphere on the total system MTF, and this is a strong function of aperture... in fact I think this is responsible for a lot of the effectiveness of small refractors for visual observing of Jupiter. I speculate (but cannot prove) that the eye-brain system is at play here too, as I wonder if one's brain does some selective shift and adding of the images. I think the visual system's timescale for detecting motion is longer than the atmospheric coherence timescale in most atmospheric models for seeing.

Bob

P.S. Anecdotally, when viewing Jupiter from my backyard (which typically has pretty mediocre seeing) my TEC MC200 Mak is always somewhat better than a C11. (I made quite a few comparisons with my now departed, and optically pretty average, C11). My TEC140 is behind the Mak, but not that far behind... both deliver pretty terrific views of Jupiter (as does an 8" f/7 Newtonian I also have, which is actually the best of them all for Jupiter, although it's the fussiest to cool down, which often spoils the fun). In a contest with a C11 I'd take any of these scopes over the C11 for visual use on Jupiter. But I'd also take a C11 over any of them for webcam imaging, since the bigger scope has more resolution and I can improve the contrast in post-processing.

P.P.S. As far as Jupiter's features that show colour in a 110mm refractor, here are my impressions. To my eyes, in addition to the coloured features you've noted, my notes for scopes with an ~4" aperture show records of reddish/brownish striations in the equatorial bands and a yellowish/greenish polar zone. And festoonal structure in the EZ occasionally shows a bit of blue to my eye, though this may be my imagination. I find a binoviewer really helps with colours.

Edited by Bob Abraham (12/09/13 07:56 AM)


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Re: Jupiter in small refractor telescopes new [Re: Bob Abraham]
      #6242037 - 12/09/13 04:23 AM

Quote:

I find a binoviewer really helps with colours.




This has been my experience as well.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6242094 - 12/09/13 07:01 AM

Eddgie, man, I am flattered from your kind words. No offense ever taken, I understand where you're coming from and buy into it as well. I appreciate you vast knowledge and appreciate what it can mean having observed in that extended higher spacial frequency range in diffraction limited seeing.

I just want to begin my reply by stating my own visual experience is very much like the SW100ED image almost to a "T." The two ovals visible represents very much the difficulty observing them. They are tiny structures and each of those three were observed over time. They probably have very low contrast. But they do roll into and mostly out of view from time to time.

The trailing wake is almost perfect with brighter arcs (ovals) across the tops and less defined fainter (smooth) cloud below. Sometimes darker cloud can be seen swooping northward into the unresolved smooth cloud features. It does indeed have a "smooth ovalish appearance" if that's what you mean.

The Festoon blue is nearly exact. The faint white clouds in the northern NEB are there, too, and the difficulty of the rifts is evident in that image. The faint hue in oval BA is sometimes seen and sometimes not while the dark spot trailing it - is sometimes a faint fuzz and sometimes a very dark pin point. Even the main belt hues, though more saturated than visual, are spot on as is the amber or tawny in the EZ and NTempZ. (Edit, actually they are a bit more reddish than visual, after looking back over my notes and sketches.) The equatorial belt is faintly seen. All of it is there. The 140mm image is too well resolved compared to visual, except for maybe some very thin, dark features in the NTB. Those can be seen thinly visually but hardly show in the 100ED image. Last year I even managed some of those blue spikes jutting north from the SEB and the darker border of that main southern belt. They looked very much like the 140mm image.

By the way, I am hoping this description is in line with Jupiter in small refractors, much like the ED 100 or maybe the 140mm - somewhere in that range or with some aspects of each. I'm not meaning to hijack the thread, its just interested and sharing experience with Jupiter in a small bore aperture (which should be closely matched by a slightly smaller refractor.)

I find it interesting, if inconclusive, that the 100ED image seems to have planetary contrast similar to a 6" obstructed visually and that the latter can pick up some finer higher frequency (and contrast) detail imaged in the 140mm APO. Visually, the view is not that good in sum as the 140mm image, but these images seem to suggest MTF is about right. To me, anyway. That real world experience, with atmospheric seeing, cooling, and collimation to contend with, and the hi res work we've done with Io and Ganymede (and a few tight double stars) seem to speak volumes about MTF and PSF theory not being far from visual experience when seeing is at least diffraction limited.

That's my $0.02, any one got change for a nickle?

Edit: reading Bob's comment above I realize breaking the cardinal rule of comparing images to visual. Yes, there is a lot going on with the eye brain, but in this case the likeness is strikingly good. Coincidence or expert processing? I'd bet the latter. However, the end result is strikingly similar, regardless. This is one reason why this thread is interesting, it's kind of a comparison thread...what we can see. What I see and what you see in different scopes and conditions. How does Jupiter look in small telescopes? Well, that's it.

I suspect the MTF is very good at describing what /should be there/ at least and when conditions are lab-like or at least diffraction limited. How one views, or processes images of, what is there given their conditions, equipment, and experience is different story.

Edited by Asbytec (12/09/13 08:03 AM)


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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6242114 - 12/09/13 07:32 AM

Hi Asbytec,
you described your view experience. Which telescope did you use?
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Bob Abraham]
      #6242118 - 12/09/13 07:37 AM

Hello Eddie hello Bob,
thank you for your interesting comments and comparisons. OK we sometimes got a little bit away from the small refractors ...
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6242132 - 12/09/13 07:59 AM

Quote:

Hi Asbytec,
you described your view experience. Which telescope did you use?
Clear skies,
Roland




A 6" Mak.


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6242150 - 12/09/13 08:21 AM

Quote:

Quote:

I think that the Semi APO will dim the view too much and does not improve the contrast much in a 80 f/15




That would be my concern as well. With these small scopes, light is precious, and always in short supply. And false color is a non-issue anyway.

BTW, I had a chance to try a 80mm f/15 Jaegers lens at a star party in September, and that was a REALLY sharp and color-free 80mm f/15. Going from memory, it was clearly better corrected for color than my Vixen 80L. It fell short of the 85mm f/19 Zeiss A, though, but then again, what doesn't?


Clear skies!
Thomas, Denmark




Incidentally, the Semi-Apo works well on Jupiter because of the properties of the Moon and Skyglow part of that filter, not just for filtering of CA.

I use a Baader Semi-Apo on my achro's but use just a Moon & Skyglow on my MCT for Jupiter. When things look a little washed out trying to get to the highest mag that seeing will accommodate for the evening, if I put in my M&SG filter, it will harden the soft view and details will "pop" substantially better than no filter.

I wouldn't be concerned with dimming too much in an 100mm or up. It's Jupiter. It's bright. I would think that an 80mm might need a little cleaner filter for this such as one of the gentler contrast booster filters or something. This filtering is good for turning your lightish brown bands with soft view into a more defined, appearance of a darker band. I also noticed it blacked the background space more and made the variations in upper and lower bands stand out more for me.

I frequently use the M&SG as my Jupiter filter in my 6" MCT.


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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: Vondragonnoggin]
      #6242174 - 12/09/13 08:44 AM

Quote:

It's Jupiter. It's bright.




In TOTAL, Jupiter is bright, but the surface brightness is rather low, and that's what's important, since surface brightness determines how much magnification you can use. A filter that removes some light WILL lower the useful magnification, unless it cleans up an image that is badly affected by false color, to the degree, that the image can take more magnification after filtration, but even then, you're left at a lower useful magnification than a telescope of the identical aperture that doesn't need the filtration.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6242201 - 12/09/13 09:01 AM

My MCT certainly doesn't need filtration for any reason, but, like many folks that prefer to use filters for planetary over non-filtered views, I just like the view through the filter better. It makes things "pop" more as described by others too.

So in appearance, filtering the view brings out more low surface brightness detail, even if optical theory says it should make them less noticeable.

As I stated though, a filter like that is probably too steep for a 60-80mm refractor where you are already struggling to get as much photons in as possible.

Also, at some point magnification, if seeing permits, will dim the view so much that using a filter is not going to be helpful and image scale to the point of last mag that offers a clear view, will be such that surface details present themselves easier.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6242223 - 12/09/13 09:13 AM

Quote:

This is such a telling set of images.

In a recent forum on Strehl, I posted a "Simulation" and I marked several details as to how they would appear in a 6" f/15 acrhomat, and at what point detail would fall below the resolution of that instrument.

If one looks at the festoon with the long tail, it is a classic example of diffraction at work.

In the 11" scope, the tail is long and consicious. It starts wit 20% or so contrast.

And in my writup on Strehl, I has suggested that this kind of freature, and ovals on Jupiter, would be difficult targets for a 6" achromat because of the loss of contrast transfer from CA and the contrast loss of the apeture itself.

I even suggested that some of these features would be difficult in a 6" APO (and I know that to be the case from my own observing experience.

And your pictures demonstrate exactly. This kind of thin, low contrast detail as shown in this long arc coming sweeping down and across is being lost completely in the 4" scope, and only hinted at in the 140mm, but clear and well extened in the larger scope.

Here is my simulation. And again, this is only a simulation, but notice how close I camse.

The black lines are about 1.5 arc seconds in length. I had suggested that the diffraction and CA in a 6" f/15 achromat would make the details that are next to them in the simulataion below the scopes contrast transfer ability.

And here we are.. Pictures that cleary show the contrast being reduced for these same kinds of features.

I just used MTF to calculate the 1.5 arc second size as being the point where th eobserver would no longer be able to detect detail at 6" with chromatic aberration, even if the apeture were otherwise perfect.

So, here is the simulation, and you pictures seem to match very well with how the simulation suggested a 6" achromat would do. Your scope is 5.5", but the polychromatic Strehl is probably on the order of .95 to .97, while in the 6" f/15 acromat, the polychromatic strehl is only about .75, though the photopic strehl (green light) is above .90

Anyway, anyone going back and forth with the simulation I did and the pictures you took I think might be surprised at how close the simulation came.

That kind of tail is difficult even in a 6" APO, and for a 6" f/15 achromat is out of reach.

Not for a C11 though, and once again, having owned one of those and compared to a 6" refractor, my result was in line with your pictures.





Eddie, where did this image come from; and with what kind/size scope??? It looks definitely processed to me.
M.


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6242312 - 12/09/13 10:14 AM

Quote:

OK we sometimes got a little bit away from the small refractors ...

Roland





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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6242433 - 12/09/13 11:21 AM

It is a simulation. Sorry if I did not say that.

It was done with Starry Night Pro.


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6242470 - 12/09/13 11:40 AM

Like Astrojensen, I also use Binoviewers (with the 110ED and 12" dob). I do mostly Solar White Light with the 110ED, but I have used it on Jupiter.

For me, besides going to a bigger telescope, the binioviewers have done more to imporve my planetary observating that any filter or eyepeice "Upgrade" that I have ever done.

And as Astrojensen suggests doing, I also tend to use less power in binoviewers than in mono mode, though I personally have not had good results even in mono-mode with much more than 1.3x per millimeter.

Lowering the magnificaiton in binoviewers does improve the brightness of the image, and as Astrojensen reports, I to agree that even though the image scale is reduced, two eyes working together are so much better at resolving small detail that even at lower powers, I am seeing more datail than I often used to see in monoviwision.

Color rendtion might be a little affected at higher powers, but once again, keeping the powers lower puts more of the diameter of Jupiter over the Foveolaa, and this is where the cones are the densest in the retina.

The reason this is important is simple. Each cone is hard wired to a neuron. This means that the resolving power of the Foveola is FIVE TIMES as good as with the rods, which are "Stacked" together so that groups of rods fire a single neuron, making the resolution of the rod dominate of the eye incapable of resolving fine detail. Great for seeing a tiger in the dark, but not good for telling if it is a boy or girl tiger or if it is looking your way I suppose.. Mostly, when you see the tiger, you really aren't intreseted immediatly knowing the sex of the tiger though..

Anyway, for me, binoviewers have become an essntial part of my planetary observing, and reducing power is not a sacrifice at all.. I see more today using less power than I have in the past in monovision using more power.

Highly recommended. I used to not be a big a fan of using them in smaller telescopes, but when I learned to back of on the power a bit (even in my larger scopes) and re-visted the configurtion in my 110ED for white light solar, it was pretty jaw dropping. A big sunspot has more detail in a 110mm apeture than the entire face of Jupiter would in the same apeture. Amazing.

And I credit my new love for white light solar to the binoviewers. Had done solar many times over the years in small refractors, but with the Binoviewers, it is a tranformational experience. I do more white light solar these days than alost anything else.

So, highly recommend binoviewers for any size scope, but have been fantasitc in my 110 refractor.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6242617 - 12/09/13 12:59 PM

Quote:

Anyway, for me, binoviewers have become an essntial part of my planetary observing, and reducing power is not a sacrifice at all.. I see more today using less power than I have in the past in monovision using more power.




This is also my experience.

And yes, the Sun is absolutely fantastic in binoviewers!


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6244012 - 12/10/13 01:52 AM

Quote:


For me, besides going to a bigger telescope, the binoviewers have done more to improve my planetary observing that any filter or eyepiece "Upgrade" that I have ever done.





Hi Eddgie:

I agree, but if you get two planetary eyepieces that are comfortable for binoviewing, it is even better!

Quote:


...
Color rendtion might be a little affected at higher powers, but once again, keeping the powers lower puts more of the diameter of Jupiter over the Fovea, and this is where the cones are the densest in the retina.

The reason this is important is simple. Each cone is hard wired to a neuron. This means that the resolving power of the Fovea is FIVE TIMES as good as with the rods, which are "Stacked" together so that groups of rods fire a single neuron, making the resolution of the rod dominate of the eye incapable of resolving fine detail...




I agree with most of what you said, but with a couple of corrections. It is true that in the fovea, you have 1:1 correspondence of cones to ganglion cells. However, outside the fovea is the 5:1 zone (still cones), and rods can be over 100:1.

I don't think that the binocular summation phenomenon (increased resolution and contrast vs monocular vision) is due to putting more of Jupiter over the fovea - do you have any references for this? My guess (and it is just a guess) is that the increased perception is due to processing, including increased noise reduction with oversampling.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6244444 - 12/10/13 10:29 AM

There was a very steady early morning a few months ago. I was amazed at how the bands appeared dark brown through a 4 inch refractor. The contrast was remarkable.

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Re: Jupiter in small refractor telescopes new [Re: PeterR280]
      #6244710 - 12/10/13 12:49 PM

Quote:

There was a very steady early morning a few months ago. I was amazed at how the bands appeared dark brown through a 4 inch refractor. The contrast was remarkable.



Hi Peter,
what kind of 4 inch refractor do you have and how much magnification did you use?
Did you see the Great Red Spot or the oval BA and how was its colour?
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6245257 - 12/10/13 05:02 PM

The GRS was not in view. I was using the C102GT at with a 6.7mm ES 82 degree. I had never seen the bands so dark. Even now.

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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6245442 - 12/10/13 06:29 PM

Derek

I think you nailed it with reduction in noise by using two eyes, over sampling. Wether it be daylight spotting, lunar observing or deepsky the spurious noise can have this graininess that comes and goes with the amount if distraction the non observing retina/brain encroaches on the viewing eye. In those moments I step back a sec and let it dissipate. I would think that even in the better moments perhaps that noise is there on a very subtle but detracting level - of which binoviewing nixes.

Pete


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Re: Jupiter in small refractor telescopes new [Re: PeterR280]
      #6246361 - 12/11/13 05:27 AM

Quote:

The GRS was not in view. I was using the C102GT at with a 6.7mm ES 82 degree. I had never seen the bands so dark. Even now.



How is your current experience with the C102GT and the Great Red Spot and the bands?
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6246876 - 12/11/13 11:51 AM

Telescope-Optics.net has a lot of detail on the eye. In fact, for astronomers, I think it is some of the most "relevant" work on the entire web.

Much work on the web is "Generic" and does not really try to translating how the science lines up to the specific application of viewing though at telescope.
Telescope-Optics.net has this as their primary focus... How the telescope eye behaves.

Even here, there is very little direct research, so the author does us the service of etrapolating or using the several difference examples for our own comparisons and conclusions.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6246915 - 12/11/13 12:22 PM

Niklo

Work has been very busy so I have not had the time for much viewing.


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Re: Jupiter in small refractor telescopes new [Re: PeterR280]
      #6257996 - 12/17/13 11:56 AM

Hello,
I have a wonderful night on December the 15th to 16th. The sky was clear after about two weeks of clouds ...
At about 10:30 pm to 10:45 I tried the sky and saw Io appear near Jupiter. The seeing was OK and so I fetched laptop and the camera. After I trying to switch on the stepping motors of my ADM mount it doesn't work so I had to use the ADM manual with only short clips of about 15 to 20 seconds.
Here some of the photos I got of my videos. I used a diagonal prism and later a diagonal mirror (there was no difference visible). In registax I used flip y to show south on the bottom of the pictures. The cloud structures in the picutres moved from right to left and Io is on the right side of the pictures.
On the left side are the moons Ganymed and Europa and on the riht side Io. Callisto was on the right side, too but too far right to be on the pictures.


At 11:03 pm (German time)


At 11:05 pm


At 11:13 pm
http://www.cloudynights.com/photopost/data/525/218055Capture_12_15_2013_11_13...

The picture of 11:13 was taken with 2x barlow but reduced to 50 percent to be in the series and show the movement of the cloud structures.

The full barlow image with f/30 is:


Then I had to go into my appartment and save the videos to an external hard drive. When I got out the seeing degraded but I took a picture when the oval BA was in the center on south *pole cap*. It's hard to see but OK


This time i did too much videos but the next time I try to watch more time.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6258758 - 12/17/13 06:47 PM

80mm scope- impressive; and nice pics.
M.


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6259454 - 12/18/13 04:40 AM

Thank you Mark, I'm really impressed, too. What telescope do you use?
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6259565 - 12/18/13 07:42 AM

Am in the process of polishing my own 8" F/8.3 refractor achromat. If apertured to 90mm, it will provide essentially semi-apo or slightly better performance according to the spotplots. Been held up with customer orders, but should be back on it soon.
M.


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6259569 - 12/18/13 07:45 AM

Actually, these pics look very similar to what I get with average atmospheric conditions with a 6" scope (reflector).
That is, seldom- especially this time of year do I get stable conditions here!
M.


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6259604 - 12/18/13 08:25 AM

If say that's average in Connecticut with Pickering 4 which is common all winter. At that P rating my 8" generally looks like a 70mm under great steady sky's in terms of detail.

Pete


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Re: Jupiter in small refractor telescopes new [Re: azure1961p]
      #6259642 - 12/18/13 08:55 AM

Jupiter is one of my favourite subjects. In the last weeks I have observed the giant planet almost every nights, mainly through a 100/1000 achromatic doublet, either as a cyclop and with a Maxbright bino (mag range 120-160, but mainly at 140x).
Due to the very warm tone provided by my refractor I rather describe the giant gas ball in gradations of ochre and "cream" (the GRS itsfel looks "caramel" I daresay).
In the last few nights I enjoyed a rather good seeing, maybe 7 Pickering, and I saw a quite mess of details inside the belts (as tone variations) and in the equatorial zone (linear structures darker, like grey on cream).


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Re: Jupiter in small refractor telescopes new [Re: Hesiod]
      #6262076 - 12/19/13 02:40 PM

I was able to look at Jupiter last three nights.

The first night, GRS was visible in 80mm AS80/1200 but I did not noticed too much of detail. Clouds came quickly in. Neither I noticed any GRS coloration.

http://www-hep2.fzu.cz/~kupco/astro/2013/2013_12_15/pic/orig/Jupiter_20131215...

Second night, I was again out with AS80/1200, this time I took out an old lens in brass. Contrast was beautiful, but again not any color:

http://www-hep2.fzu.cz/~kupco/astro/2013/2013_12_16/pic/orig/Jupiter_20131216...

Last night, I took larger refractor ED100. GRS was placed favorably and I could finally see its dark-orange/grayish color:

http://www-hep2.fzu.cz/~kupco/astro/2013/2013_12_17/pic/orig/Jupiter_20131217...


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6262128 - 12/19/13 03:09 PM

I was lucky enough to catch a few hours of clear skies yesterday evening. The seeing was not so good, unfortunately. At first, I was limited to 64x on the 85mm f/19 Zeiss A apochromat (25mm Zeiss eyepieces, Baader Maxbright bino), but later, I was able to use 106x, although the results were mediocre. But I was fortunate to catch Europa near the end of a transit. The shadow had already left Jupiter, but Europa could be seen as a small, bright blob in SEB, near the limb of the planet. At first, I thought it was a disturbance in SEB, but in seconds, I realized, what it was. I watched as Europa moved over the limb and increased the distance to Jupiter, although I was sometimes disturbed by clouds. Europa was a tiny, tiny little white disk, very sharply defined. It was clearly smaller than Ganymede, but with higher surface brightness. Ganymede had a beautiful golden color. Io was rosy pink! Callisto was grey and colorless.

After the transit ended, I experimented with my old 0.965" Zeiss and Kokusai Kohki orthos and compared them with my 25mm Zeiss microscope eyepieces in the Baader Maxbright binoviewer. The binoviewer won effortlessly. I could see a LOT more details and with a lot more certainty and far less effort. I compared with approximately the same magnifications in mono and bino and also tried higher magnifications, to see if I could see the same in mono, if I used higher magnifications. On the Moon, this was true, but not on Jupiter! The same magnifications mono and bino felt like 50% higher on the bino, while the contrast was MUCH better and the sharpness was the same or better, because of using two eyes.

The Moon in the bino, using 64x and 80x was utterly fantastic. The contrast and sharpness of the 85mm with bino is simply staggering.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6262344 - 12/19/13 05:21 PM

Hi Alexander,
congratulation for your nice sketches and for your orange Great Red Spot. I think you will soon the little orange even with you 80/1200. Once you learned to see it you will see it even in the smaller refractor.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6262353 - 12/19/13 05:26 PM

Hi Thomas,
great so you saw Europa in front of Jupiter that's great and you seen colours on the moons. I haven't tried that yet. The orange of the Great Red Spot is for me much easier than seeing colours on the moons
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6263021 - 12/20/13 03:58 AM

Hi Roland

The colors of the moons is seeing dependent, too, as the subtle hues tend to get washed out in poor seeing. GRS was unfortunately not in sight during my last observation. It is much bigger than the moons, so the color is easier to see. I think the colors of the moons *might* be easier to see in an apochromat or a reflector. In my 4.5" f/10.7 achromat (stopped down 150mm f/8) they are all yellow.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6263033 - 12/20/13 04:51 AM

Hi Thomas,
I had and still have a 114/900 newton but I haven't seen colours of the moons. Which magnification do you use? Is it better to use around 100x or less or more?
The small Vixen 80L has less CA then the 4.5" f/10.7 so I can try both with the Vixen and with the 114/900 newton (which has less optical quality than my Vixen 80).
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6263069 - 12/20/13 06:21 AM

I saw that Wallmart had a Celestron 70mm F/10 for about $50.
I'm not recommending it, but just curious. Would this scope be worth the trouble? Has anyone used one? I'm not affiliated with either company/corporation.
***
I'm just guessing, but I think from what is posted here, a slightly longer focal length than what this has could be helpful.
What do you guys that post here recommend?
M.


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6263159 - 12/20/13 08:21 AM

Hi Roland

I saw the colors of the moons at 106x with the bino. In the past, I've seen them with mono as well, using similar or higher magnifications. The moons can take more magnification than Jupiter, especially Ganymede and Io. Callisto has low surface brightness and becomes very fuzzy at high power.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6263829 - 12/20/13 02:12 PM

Hi Mark

Quote:

I saw that Wallmart had a Celestron 70mm F/10 for about $50.
I'm not recommending it, but just curious. Would this scope be worth the trouble? Has anyone used one? I'm not affiliated with either company/corporation.
***
I'm just guessing, but I think from what is posted here, a slightly longer focal length than what this has could be helpful.
What do you guys that post here recommend?




I am not sure these have the optical quality to make them worth it. Theoretically, a 70mm f/10 should be able to perform well, but I am not sure about these low-price scopes. I would probably stay away from it and try to find a used Vixen 80/910mm achro or better yet, any of the old 80/1200mm achromats from Japan, or maybe a Jaegers.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6264731 - 12/21/13 01:23 AM

Quote:

Hi Roland

The colors of the moons is seeing dependent, too, as the subtle hues tend to get washed out in poor seeing. GRS was unfortunately not in sight during my last observation. It is much bigger than the moons, so the color is easier to see. I think the colors of the moons *might* be easier to see in an apochromat or a reflector. In my 4.5" f/10.7 achromat (stopped down 150mm f/8) they are all yellow.


Clear skies!
Thomas, Denmark




Very true and I find not even so much poor seeing but anything less than good seeing and the colors diminish or disappear altogether. It never ceases to amaze me how when seeing settles and the image sharpens how the color reconstitutes. Titan with my 8" is a good example .

Pete


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6266467 - 12/22/13 06:42 AM

How about some pictures of our 80mm refractor setups we use for our observations? Here's a photo of my 85mm Zeiss, actually taken during my last observing session, described above, with the scope actually pointed at Jupiter.



It's not exactly the small, portable 80mm's we think of today, when we think of an 80mm refractor. The mount is an EQ-6 on a large Baader hardwood tripod.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6266534 - 12/22/13 08:59 AM

Nice scope. Would like to see what others have, too.
M.


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ggalilei
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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6266648 - 12/22/13 10:51 AM

I'm still at the bottom of the learning curve, but I'm starting to get the feeling that there are differences in Jupiter's colors depending on the eyepiece used. I mostly observe with Naglers and see warm colors, like cream and brown, but in the Tak LE I saw colder tones, leaning toward white and blue. Is it just my old eyes, or a random veil of high altitude clouds, or is it a real effect?

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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: ggalilei]
      #6266658 - 12/22/13 10:55 AM

The effect is real. In some of my plössls and kellners, I see a warmer, yellower tone, in my Zeiss and ES 82's, I see a more neutral or colder image.


Clear skies!
Thomas, Denmark


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6267418 - 12/22/13 07:03 PM

Hi Thomas,
your combination looks really great. How much does the hardwood tripod weight and how much the mount? How high is it and where did you get the hardwood tripod?
Currently I have just a Celestron ADM. The steel tripod with the mount and counter balance does weight about 21 kg.

I try to find a new picture of my Vixen 80L
Clear skies,
Roland


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JonM
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6267488 - 12/22/13 08:04 PM Attachment (38 downloads)

Here's sho taken with an EON 120 with a 5X powermate.

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mikey cee
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Re: Jupiter in small refractor telescopes new [Re: JonM]
      #6267604 - 12/22/13 09:24 PM

Jon that is a hell of an image with a 4.7" scope. What camera and what settings did you use?? Very well done. Mike

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Niklo
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6267882 - 12/23/13 03:14 AM

Hi Thomas,
here is a picture of my Vixen 80L on the Celestron ADM before starting to watch Jupiter.

The ADM is solid but heavy. Maybe a wooden tripod would make it less heavy.
Clear skies,
Roland


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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6267950 - 12/23/13 05:07 AM

Hi Roland

Quote:

your combination looks really great. How much does the hardwood tripod weight and how much the mount? How high is it and where did you get the hardwood tripod?




The scope itself weighs around 11kg with rings, diagonal, eyepieces, etc.

The mount weighs 17kg

The tripod 11kg

The counterweights 11kg

Total around 50kg, give or take a kg or two. It's not something you just pick up and move around in the garden. I can carry the mount and tripod as a unit, but not with the counterweights or the telescope attached.

The tripod is a Baader Hardwood tripod, which I bought directly from Baader Planetarium. It is ~110cm tall with the legs not extended. I never use them fully extended. It can be up to 155cm tall. It is very solid, yet easy to handle. In fact, the EQ-6 plus tripod is much easier to handle than the EQ-6 with the original tripod, since the original tripod was much wider and couldn't be carried fully assembled through a normal door. And when the mount was removed from the original tripod, the legs were loose and the tripod became uncomfortable to carry, in my opinion. The Baader tripod is much nicer. There was also a lot of flexure in the original tripod, when it was loaded with the long and heavy 85mm Zeiss, while the Baader is stiff and solid. My EQ-6 became like a whole new mounting with this tripod.

Unfortunately, it's currently out of production (Baader sometimes stop production of some of their items, when they want to make changes and such), but you can sometimes find them used.


Clear skies!
Thomas, Denmark


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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6267957 - 12/23/13 05:18 AM

BTW, I think I've shown it before, but here's my Vixen GP 80L. It's the last version sold in Europe, with the green GP mount, W-135 tripod, original 50mm finderscope holder, 8x50 Antares finderscope and M36.4x1 prism diagonal. Originally the scope had an 8x30 finderscope, which was incredibly sharp, but a bit uncomfortable and a little on the dim side, although it had no trouble showing M81/82 or the Eskimo nebula. The RACI Antares finder was a big step forward in comfort.



I relocated the spreader and tray downwards, to allow the legs to have a steeper angle with the ground. This looks more classic and doesn't take up as much room inside. It also mean that I hit the tripod legs with the scope less than I did before. I really would like to have an original 110cm Vixen pillar for this scope. I have a weakness for refractors on pillars.


Clear skies!
Thomas, Denmark


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6267973 - 12/23/13 05:59 AM

Hi Thomas,
wow, 11 kg for the telescope. It's much more than the small Vixen 80L which is about 3 kg. OK my combination is much lighter but I cannot go through doors with the tripod so maybe a wooden tripod would be an improvement for me, too.
What does your Vixen 80 combination weight? Is it possible to add a motor on the Vixen mount for taking photos?
Clear skies,
Roland


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: JonM]
      #6267976 - 12/23/13 06:04 AM

Quote:

Here's sho taken with an EON 120 with a 5X powermate.



Hi Jon,
that's really a nice Jupiter. Is the EON 120 an ED refractor or an APO? How is the view in the eyepiece? Which magnification is your favorite for Jupiter?
Clear skies,
Roland


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jag767
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6268056 - 12/23/13 07:40 AM Attachment (37 downloads)

Here's what I've been looking at Jupiter with lately. With its small size the view is quite remarkable.

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aa6ww
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6271535 - 12/24/13 11:57 PM

Jupiters GRS is going to start its transit in about an hr and a half from now. It should be fun to watch. My TSA-102 had been out on my patio for about 3 hrs, so its time go got start playing with it. Its transit is dead center at 11:42pm tonight PST, so roughly an hr on either side of that is when its fun to watch and test your optics. Seeing again is excellent tonight here in calif, and the moon should help contrast!

... Ralph


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Sasa
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Re: Jupiter in small refractor telescopes new [Re: aa6ww]
      #6272761 - 12/25/13 09:19 PM

Due to illness I missed several opportunities to observe Jupiter. Last time, it was December 20:



Again in AS80/1200. I found interesting a direct comparison with this image from ALPO Japan pages which was taken at the same time as my drawing (the image on the left):

http://alpo-j.asahikawa-med.ac.jp/kk13/j131220b2.jpg

Most of my observations were made at 96x (CZJ O-12.5). As seeing was not the best, I used the higher magnifications (120x, CZJ O-10 and 150x ATC 8E) only to confirm some features and to place them more correctly - Jupiter is really tiny at power of 96x... As you can see in the comparison with the image, I still made some mistakes. I also noticed different coloration between eyepieces. CZJ orthos were providing Jupiter's surface with more yellowish (or yellow-brownish) tint while ATC 8mm Erfle eyepiece was visible whiter. I was using strong white LED light for sketching but still I could not see any definite colors on Jupiter's belts.

Sorry, I have no pictures of this setup yet. Its just an old home-made OTA that came with the lens. I gave it a new baffles made out of plywood and paper, and I equipped it with old Zeiss helical focuser and finder:

http://www-hep2.fzu.cz/~kupco/astro/equipment/AS80_1200/as80_1200_vytah.jpg

You can find some more pictures and info on this web page:

http://www-hep2.fzu.cz/~kupco/astro/equipment/Zeiss_AS80en.html

I do not use dew shield. When the lens gets wet I simply replace it with the second AS80/1200 lens. The telescope sits on Sky Watcher AZ-5 alt.-az. mount and wooden tripod.


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azure1961p
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6272910 - 12/25/13 11:16 PM

Nice work Alex. I can sympathize with your bad seeing being in Connecticut in winter. You switch out your objective when the other gets dew!!!!!! Aren't there collimation issues here? First time Im hearing if this *technique*!!!

Incidentally that almost exactly how Jupiter looked to me last night with my C6!

Pete

Edited by azure1961p (12/25/13 11:18 PM)


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AllanDystrup
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6273064 - 12/26/13 02:51 AM

Quote:

I do not use dew shield. When the lens gets wet I simply replace it with the second AS80/1200 lens...




Well, if that aint the epitome of luxury, Alexander...

-- I like it

The AS80/1200 btw is the only AS-lens to my knowledge (apart from the small AS63) with half-apo secondary spectrum correction. And a very nice OTA you've got for the lens!

Allan


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Sasa
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Re: Jupiter in small refractor telescopes new [Re: azure1961p]
      #6273075 - 12/26/13 03:22 AM

Hi Pete, a change of AS lenses is a one minute task. If you look at the lens images on my web page, you could see that they have threads. You can simply screw them in and out. This is very nice feature. I can keep my AS110 lens at home and install it only when I visit my dark-side observatory. I keep there permanently only OTA. I would be afraid of leaving such an old lens in this remote side. It is also handy even with AS80. I can manipulate with long tube in more crude way.

As for collimation, none of my Zeiss tubes has collimated cells. But it should not be an issue at f/15.

Cheers,
Alexander


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Sasa
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Re: Jupiter in small refractor telescopes new [Re: AllanDystrup]
      #6273108 - 12/26/13 04:46 AM

Thanks Allan, I like it too. It may sound a little bit snobbish but it is good opportunity to take out from time to time the old brass lens under the stars. I usually observe with late AS80 lens. Weather in winter rarely allows longer sessions anyway. And that late AS lens is far from being a luxury item. The whole setup including the eyepiece turret and two CZJ ortho eyepieces cost me about the same as the ATC 40mm Kellner that I bought new to fill the M44 thread in the turret. The lens is not in top state. But it still provides visibly better views on planets and Moon than my 80/480 Lomo triplet.

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Niklo
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6273154 - 12/26/13 06:32 AM

Hi Alex,
thank you for your nice sketch again. It's really difficult to draw. Maybe I'll try it, too, but with bad seeing I wouldn't even try it because the details can be seen too short time.
Things like the spot group in the south "pole cap" are only possible if the seeing is very good but in your pictures there already a hint of the spot group (white ovals). The line on your pictures breaks there. The northern belts are easier but even there good seeing is important.

I wish you clear skies with good seeing and healthiness.
Roland


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: AllanDystrup]
      #6273168 - 12/26/13 07:03 AM

Hi Alan,
yes a second AS 80/1200 objective that's not bad

The AS110/1650 should be close to a half apo and if you reduce the aperture to 100 mm than you could probably have a real 100 mm half apo and reducing to 3" you are pretty close to an 3" APO, too, but probably it's better to use the full aperture with a little CA. The CA of the AS110 similar to the Vixen 80L should not be a big problem.

Yes, the OTA of the AS80 looks very nice. It's a pity that Zeiss has stopped the production....

Clear skies,
Roland


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AllanDystrup
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6273939 - 12/26/13 04:15 PM

Extraordinary, Alexander, that you were able to get the whole AS80/OTA/Turret for the same price as one ATC 40K eyepiece... That was a lucky punch indeed !

A great eyepiece, the ATC 40K; I just received the 8mm 62dg 'Nagler type' EP from ATC; I've only had a chance to test it in my Telemator on the moon and Jupiter on one evening with mediocre transparency -- high humidity, with slowly increasing high freezing fog... Looking good! But I'll withhold my judgement till I've had a chance to push the eyepiece on a night with fair seeing and transparancy.

Allan


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karstenkoch
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Re: Jupiter in small refractor telescopes new [Re: AllanDystrup]
      #6274826 - 12/27/13 04:01 AM

Enjoyed a nice view of Jupiter a few weeks ago with an ES82 4.7mm in my AT72ED. Jupiter was near the zenith, so the light weight of the 4.7 really took it easy on the focuser. I'm sure it is bigger in my memory than it was looking at it in the eyepiece, but I was very pleased with the quality of the view. I remember seeing multiple bands and zones with no trouble. GRS was missing from the view. Been plagued with you know what overhead almost every night since.....

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Mark Harry
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Re: Jupiter in small refractor telescopes new [Re: karstenkoch]
      #6274919 - 12/27/13 07:54 AM

I used a cheap homemade refractor with an 80x700mm lens, and a 24 Panoptic. Only 29x magnification, but I saw Jupe in the WNW with both main equatorial bands, and a couple unequal brightness/size moons simply propped on the open window. I didn't notice any color issues, but probably non-existent at that power setting. Very calm and cold conditions, transparency decent. I need to adapt a mount for this scope.
M.


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JonM
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Re: Jupiter in small refractor telescopes new [Re: mikey cee]
      #6275447 - 12/27/13 02:06 PM Attachment (16 downloads)

I used a Imaging Source IS-618CU USB Color CCD Camera witha 5X powermate on my EON 120ED. I use Sharpcap to capture and Registax to align and combine and Photoshop to finish up. Here's another usiong a SPC900 webcam

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Sasa
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Re: Jupiter in small refractor telescopes new [Re: JonM]
      #6275710 - 12/27/13 04:36 PM

Felt a little bit better today. I had a short view on Jupiter. Seeing was cooperating again, except about 20 seconds for which I did not know where to look first. I tried to remember at least as much as details I could from SEB:



Jupiter was almost at the same position as last time when I was looking at it with 80mm refractor. I would say that in those 20 seconds, the amount of detail was notably better in 100mm refractor (as it should).


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Hesiod
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6275841 - 12/27/13 06:13 PM Attachment (24 downloads)

I tried a shot with my ASI120MM (no nice colors , but I bought the camera for solar shooting) and a 4" refractor. Seeing was good, at least Pickering 7, and the transparence was quite good too.

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JonM
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6275991 - 12/27/13 07:30 PM

"Hi Jon,
that's really a nice Jupiter. Is the EON 120 an ED refractor or an APO? How is the view in the eyepiece? Which magnification is your favorite for Jupiter?
Clear skies,"

Roland

Hi Roland,

The EON is an FPL-53 doublet which can show a little color but, is an ED scope and has a very nice figure to the lens, well polished. I used about 200X-225X for Jupiter during visual but I am mainly into Astro-Photgraphy now. I only have refractors and just got a TEC 140 which I hope will give me even better shots of the planets but, it's still a small aperture compared to the C-11 and C-14 that guys use to get the best planetary shots.


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Sasa
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Re: Jupiter in small refractor telescopes new [Re: Hesiod]
      #6276504 - 12/28/13 01:32 AM

Hesoid, very nice shot. What was the time? It looks like the very same orientation as on my drawing. The view was very similar in those 20 seconds in my ED100. Of course with much less contrast.

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Hesiod
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6276631 - 12/28/13 05:01 AM

Thanks very much! I shooted at 21:40 (GMT+1, I am in Italy).
I forced the wavelet filter, at the EP there was less contrast but a somewhat "richer" image


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Sasa
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Re: Jupiter in small refractor telescopes new [Re: Hesiod]
      #6276670 - 12/28/13 06:35 AM

Great, it was the same time then. I will keep your image as a reference, if you don't mind. It is rare to find images made at the same time and with the same aperture as my sketches.

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Hesiod
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6276718 - 12/28/13 07:47 AM

...you are too generous. If I manage to improve the pic I will post the new version

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wormstar
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Re: Jupiter in small refractor telescopes new [Re: Hesiod]
      #6276758 - 12/28/13 08:35 AM

That's pretty cool (image and drawing from same time )proves that you were accurate

Edited by wormstar (12/28/13 08:35 AM)


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obin robinson
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Re: Jupiter in small refractor telescopes new [Re: wormstar]
      #6278314 - 12/29/13 12:15 AM

Based upon this thread tonight I decided to try out the ST-80 on Jupiter. I didn't have high hopes at first but after some swapping out of components I was blown away! The combination that worked for me was:

ST-80 (with aperture mask on and scope stopped down to 42mm) + vintage Lumicon diagonal + OPT 3-Element 5x Barlow + Parks 12mm Kellner

That combo made Jupiter look great! I could see the planet in razor sharp detail and could count several cloud bands! I am definitely going to do this again and try other eyepieces as well.

obin


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t.r.
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Re: Jupiter in small refractor telescopes new [Re: obin robinson]
      #6278627 - 12/29/13 08:01 AM

Throw a yellow #8 filter on and use the scope at full aperture and resolution up to 133x!

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obin robinson
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Re: Jupiter in small refractor telescopes new [Re: t.r.]
      #6278960 - 12/29/13 11:27 AM

I will try that. Thanks!

obin


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Mike Lynch
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Re: Jupiter in small refractor telescopes new [Re: obin robinson]
      #6280878 - 12/30/13 11:17 AM

Let me toss in my two-cents worth here to confirm some of the comments already made:

I watched the recent Ganymede transit of Jupiter with my 90mm f/8.8 refractor. I had a frustrating experience trying to see detail on Jove the previous evening, but I wanted to give it another try. I am VERY happy I did!

Based on comments here and in other forums, I "backed off" from trying to use a higher magnification, and "settled" for my 6mm orthoscopic, to start with, and a Baader Moon & Skyglow filter.

What made the real difference, though, was that I simply relaxed on my observing chair and kept looking through the eyepiece at the planet until my observing eye adjusted to the view. I also patiently waited for the moments of better seeing, because the view would "fuzz out" regularly, due to the atmospheric conditions....though it was clear during the observation.

I was amazed at what happened. I not only saw the moon's shadow (which was obvious), but I began to realize that there was a small spot near the GRS. I assumed I was seeing some transient event in Jupiter's clouds.

But when I checked photos of the event the next morning, I realized I had actually seen Ganymede itself!! I was shocked at that...thinking a much larger scope was needed to see it.

During the moments of much better seeing, a train of white material in the SEB became visible, the shape of the edges of the NEB could be seen, and the regions nearer to both poles actually showed just a bit of detail.

My best views were with the 6mm ortho and a 12.5mm ortho combined with my Orion Shortly 2x Barlow through this 90mm scope.

It was the most satisfying evening of observing in quite a while! And through a small refractor, at that!


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rockethead26
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Re: Jupiter in small refractor telescopes new [Re: Mike Lynch]
      #6280894 - 12/30/13 11:22 AM

Quote:

Let me toss in my two-cents worth here to confirm some of the comments already made:

I watched the recent Ganymede transit of Jupiter with my 90mm f/8.8 refractor. I had a frustrating experience trying to see detail on Jove the previous evening, but I wanted to give it another try. I am VERY happy I did!

Based on comments here and in other forums, I "backed off" from trying to use a higher magnification, and "settled" for my 6mm orthoscopic, to start with, and a Baader Moon & Skyglow filter.

What made the real difference, though, was that I simply relaxed on my observing chair and kept looking through the eyepiece at the planet until my observing eye adjusted to the view. I also patiently waited for the moments of better seeing, because the view would "fuzz out" regularly, due to the atmospheric conditions....though it was clear during the observation.

I was amazed at what happened. I not only saw the moon's shadow (which was obvious), but I began to realize that there was a small spot near the GRS. I assumed I was seeing some transient event in Jupiter's clouds.

But when I checked photos of the event the next morning, I realized I had actually seen Ganymede itself!! I was shocked at that...thinking a much larger scope was needed to see it.

During the moments of much better seeing, a train of white material in the SEB became visible, the shape of the edges of the NEB could be seen, and the regions nearer to both poles actually showed just a bit of detail.

My best views were with the 6mm ortho and a 12.5mm ortho combined with my Orion Shortly 2x Barlow through this 90mm scope.

It was the most satisfying evening of observing in quite a while! And through a small refractor, at that!




MIke,

You had the exact experience that I described here which you may have referred to in your post.

I agree that it was one of the most enjoyable observing sessions I've had in a while.


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Mike Lynch
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Re: Jupiter in small refractor telescopes new [Re: rockethead26]
      #6280967 - 12/30/13 12:04 PM

Jim,

Thanks! Actually, while I was looking around for other people's experiences with small scopes, I don't think that I saw the particular thread you linked to... But it's very "confirming" to know that others experience similar things.

Admittedly, I wondered if some people might have trouble actually believing I saw Ganymede itself!

This will get me looking for more detailed objects with the 90mm... like the "extra" stars in the Trapezium!


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pdxmoon
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Re: Jupiter in small refractor telescopes new [Re: Mike Lynch]
      #6281689 - 12/30/13 05:24 PM

A few nights ago I looked at Jupiter with a 6mm ep through my $29 Meade 60mm scope--the one I got on sale this summer.

I saw a lovely view, complete with stripes and what were clearly four moons.

It took me exactly 35 seconds to set up, point (without a view finder--using a 20mm ep) and be observing. I keep it outside, by my door, all year long.

It was a thrill and my Christmas guests were excited as well.


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aa6ww
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Re: Jupiter in small refractor telescopes new [Re: pdxmoon]
      #6281719 - 12/30/13 05:41 PM

The seeing conditions late week and last night have been spectacular. I have friends that come up with every excuse in the book why not to take out there scope when its cold.
Their loss. They are missing the absolute best seeing conditions of the year right now, and missing the opportunity too observe jupiter with unbelieveable details.
Ive used everything from my TV-85 to my C14 in the last week, all on Jupiter, all with my binoviewer.
Its an experience you cant talk about, you just have to witness it.

...Ralph


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Re: Jupiter in small refractor telescopes new [Re: aa6ww]
      #6281788 - 12/30/13 06:22 PM

I observed Jupiter tonight with my 85mm Zeiss apo. Initially, the seeing was very good, with some really good moments. The details visible in the binoviewer with two 25mm Zeiss microscope eyepieces at 106x was ridiculously good! In the very best moments, festoons popped out all over the equatorial zone. Unfortunately, the seeing very soon began to deteoriate, so I didn't get their positions pinned down as good as I wanted. I could also see some big, vague spots in the southern temperate zone, which completely stunned me. I've never seen that before.

Additionally, there was an Io transit as well as a shadow transit. Io's shadow was extremely sharp and well defined. I estimated its diameter to be not more than 1/3rd the width of the SEB, if not somewhat less. Io itself, just before ingress, was not larger. Io was clearly visible just inside the limb, where the limb darkening is pronounced. As it moved further inwards, it became more difficult to see and soon became invisible to me. However, some time before it disappeared, it looked clearly elongated to me, in the best moments. I was completely taken by surprise by this. I have heard of this before, but I honestly didn't suspect it to be visible in a scope this small and I was not looking for this effect, when I saw it. unfortunately, clouds and haze began to move in again and I missed egress, so I couldn't check again.

Right at the start of the observation, all four moons could be seen and in the good seeing I could readily identify them with 100% certainty. Later I observed them with 209x on the binoviewer. With this magnification, their size differences were obvious. Ganymede and Europa were relatively close to one another and Ganymede was clearly by far the largest. Callisto sat on the other side and showed a very dim disk at this magnification, but the disk was clearly larger than much brighter and smaller Europa. At 89x with a super crisp 18mm ES82 (one of the sharpest eyepieces I've ever seen and I've seen some stuff), I compared the moons with the width of the equatorial belts. At this magnification, Ganymede was about as wide as SEB and Io as wide as NEB. At 209x on the bino, both were seen to be much smaller, clearly showing that an 85mm can show the true diameters. Once I magnify the moons enough that they show a sharp disk, roughly 106x with the bino and 140x - 150x mono, the moons retain their sizes relative to the equatorial belts with increased magnifications, they don't get larger or smaller relative to the belts.

I am dumbfounded by the staggering amount of details the old 85mm shows on Jupiter with the binoviewer, as well as in mono with my 11mm ES82 eyepiece. The bino is clearly the best and I never saw such detail before in all my years using orthos in mono, but the 11mm ES82 also seems to have the upper hand on the orthos, probably because it is so much more relaxing to use. I will also add that it is one very crisp eyepiece, there is nothing fuzzy about it at all. Jupiter appeared like it was painted to the eyepiece, it was that good, colors and all. It was a darn shame GRS wasn't out, though I think I caught the very last glimpse of it as it rotated away from the face of the planet.

I've gathered lots of info and some rough sketches, trying my best at placing all the subtle details. I'll try making a more finished sketch as soon as possible.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6282738 - 12/31/13 04:10 AM

Thomas,

we were observing probably at the same time. I went this time to my remote observatory and at the end of 2 hour DSO session I looked at Jupiter. This was completely different level from what I usually see from my garden in my smaller refractors. As you were saying , the equatorial festoons were very easy to see across its surface. Normally, I need to use averted vision and they jump for a moment or two, but this time, there were there with direct vision and nicely visible for about 50% of time.

Also the number and smoothness of gray tones was remarkable (still no colours). No idea, if it just a better optics, 1cm more of diameter, or just better seeing and conditions at that place (or just my bad memory...). But I was saying, why I was observing faint, hardly visible fuzzies, when such beauty was right in front of my nose.

I could not concentrate too much after 2 hours in this cold weather but I tried to make at least quick sketch (I'm sure, there are many mistakes):



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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6282789 - 12/31/13 05:43 AM

Hello Thomas,
thank you very much for your nice Jupiter observation report. You described it so good that I can imagine how it looked like in your eyepieces (I almost see it
I'm very curious to see a Jupiter sketch from you but even your detailed report shows the details you saw.
I wish you a nice change of the year into a goog, healthy, happy new Year 2014. Of course I wish the same for all readers of the thread ...
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6282799 - 12/31/13 06:02 AM

Hello Thomas,
thank you for the nice and detailed sketch. I think that you even draw oval BA. It's a very good sketch and I can imagine how nice Jupiter looked in your eye piece with the festoons ...
Don't mind with the colours invisible or visible. In small telescopes it's difficult and colours are very weak/faint. So it's not a shame to see just greyish colours. The bands looked rather greyish with only a hint of brown and red in my Vixen 80L, too. Only the Great Red Spot is easier with its orange colour for me. I can see the orange and I'm very happy that I can see it after several years of a grey Great Red Spot (I watched Jupiter several years in the 90s with a 114/900 newton. During this time it did not see any colour in the Great Red spot. Often I even was unsure if the southern equator band was just a little bit thicker ...).
I wish you too a nice change of the year and all the best.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6282942 - 12/31/13 08:44 AM

Nice observing report Thomas. I'm living vicariously through your reports as winter is in full swing here and observing for me is a distant memory! I had many wonderful planetary views with my 90mm apos and for me, this size really delivers while not being too big and still remaining grab and go. Remember that in this size aperture, you are really seeing the airy disc of the Galilean satellites, the discs themselves are not resolvable below a 4", but I do know what you mean and I could always make out which one was which by the hard, clean disc size my 90's put up. Keep reporting your sessions...it's all I got!!!

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Re: Jupiter in small refractor telescopes new [Re: t.r.]
      #6283046 - 12/31/13 09:45 AM

Quote:

Remember that in this size aperture, you are really seeing the airy disc of the Galilean satellites, the discs themselves are not resolvable below a 4"




I think that is wrong. If I was not able to resolve the disks of the moons, then their sizes should depend on their brightness, just like stars, yet dim Callisto is clearly larger than very bright Io. Ganymede is larger still, and is the brightest overall, yet its surface brightness is lower than that of Io and Europa... At 209x with the bino, their respective sizes match those of high-resolution images perfectly, both in comparison with each other, but also compared to Jupiter and his belts. They do not appear larger than they should and no "diffraction enlargement" appears to take place.

Quote:

Keep reporting your sessions...it's all I got!!!




I will, weather permitting. Weather actually looks very promising right now and there's a double shadow eclipse of Io and Ganymede this evening, but of course it has to be new years eve and I am invited out to dinner at my sisters place...


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6283102 - 12/31/13 10:10 AM

It is correct...you are seeing the airy disc of some of the moons and its relative brightness is creating a different disc size which you are interpreting as the actual surface. The resolution of an 85mm is 1.3 arc sec. The Galilean moons are smaller than this,except Ganymede and maybe Callisto, therefore their discs cannot be resolved and any object smaller produces an airy disc spot...yes, it does look like a resolved moon though! It takes a 4" to 5" to begin to resolve these moons and a 6" to see them all! This topic has been discussed here many times...see this link and go down to EdZ explanation...

Jupiters Moons



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Re: Jupiter in small refractor telescopes new [Re: t.r.]
      #6283226 - 12/31/13 11:14 AM

But I am telling you, that is wrong! If their diameters were to depend on diffraction, then the diameters would depend on their total brightness, as it does for stars, but that is not the case.

How come I can see a larger, dimmer disk for Callisto, than I do for smaller, brighter Io, then? Please do explain that to me. That is totally opposite how diffraction works for stars.

Also, the resolution of an 85mm is not strictly 1.3". The airy disk diameter, as measured from the middle of the first minimum, is 3.25". The diameter of the spurious disk of a star will depend on its brightness and for a star of roughly mag 5 - 6, it's around 1.3" or the same as Dawes limit. This is not a coincidence. For a fainter star, the visible spurious disk is even smaller. It only appears not to shrink, because the resolution of our eyes get worse in dim light.

If we say the moons are build up by an infinite number of diffraction disks (I often hear this argument), then we logically must assume each tiny diffraction pattern to be infinitely faint!!!

But we can't calculate with infinity. Let's do a thought experiment. Io's visible surface area is very close to 1 square arc second (a circle with a diameter of 1.12" has a surface area of 1 square arc second). Its total magnitude right now is 5.5, not counting in extinction. If we divide the surface in 100 equally large parts, each part will shine with the light of a mag 10.5 star, on average. If we divide the surface into 10,000 parts, each part is only as bright as a mag 15.5 star and so forth.

Each of these parts is faint enough to require averted vision to detect in a 85mm (or not even detectable!), yet the moons are tiny, looks bright and brilliant. How come? Because all that surface adds up, though each part is too faint to show a diffraction pattern. It is exactly the same as with M33, that, while each square arc minute of it shines only with the light of a mag 14 star, it is bright enough to be visible in binoculars, since all the parts combined shine with the light of a mag 6 star, though spread over a much larger area.

So then how come a mag 5.5 star shows a larger spurious disk than a bunch of tiny specks only adding up to a 1.12" diameter disk? Because the surface brightness of the extremely tiny actual disk of the star is very much higher than that of the moon disk in the example. The actual disk of the star has the same surface brightness as the Sun (or higher, in many cases!). This is high enough that diffraction shows up strongly and creates a clearly visible pattern. Now, I am NOT saying diffraction does not happen on the moons of Jupiter, what I am saying is that the effect is very much smaller than for a star, being essentially invisible, the moons only being visible because they have an actually visible surface the scope can resolve and thus show the object.

So, if the resolution does not depend on diffraction, as it does for stars, then what does it depend on? Contrast. And the moons can be resolved, because they are very high contrast disks set against a totally dark background. The contrast is very high. It is similar to detection of the Cassini division in Saturn's ring. It is detectable, even when less than 1" wide, because it has very high contrast with its surroundings.

We really should stop thinking about Dawes limit when we discuss telescope resolution. We should think of our scopes as actually having almost infinite resolution, were it not for diffraction. If the target we observe is bright enough, diffraction will show up and be the limiter. If the brightness of each tiny part of the image is too faint for diffraction to be the limiter, we should think about contrast detection instead.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6283240 - 12/31/13 11:21 AM

You make a good argument Thomas and I don't doubt what you say...But others say different. And please, don't take offense, your tone seems, testy. None intended here. It is opposition time for Jove and that puts Ganymede and Callisto resolvable in an 85mm, but not the others. THere was another much longer thread than the one I linked on this topic and the consensus from many posters, some professionals, was that EdZ has it right. I base my viewpoint on what was decided there. Perhaps others will chime in or can link that discussion.

Here EdZ expands that first post...

Moons



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Re: Jupiter in small refractor telescopes new [Re: t.r.]
      #6283865 - 12/31/13 04:13 PM

It was not my intention to sound testy or angry, but I have a great difficulty to convince people of what I - and they - are able to see.

I didn't need to read a lot of the article in the latest link to see at once, that EdZ is also getting it wrong. He writes that Ganymede, visually, appears as large as its own diameter, plus diffraction equal to half the airy disk or so, about the same as a 5th magnitude star.

If that was the case, Ganymede would appear some 3" across (1.7" + 1.3"), as seen in an 85mm scope. That is more than 1/15th the diameter of Jupiter or about as wide as NEB. Does it appear that wide? At low magnification, yes, due to the limited resolution of the eye, but at high magnification, Ganymede appears less than 1/2 as wide as NEB, as it should. And the other moons are smaller still. It wouldn't if it grew with diffraction.

It would also then appear much fainter than it does, compared to a star of equal magnitude, since the light of Ganymede would be spread across a much larger area than that of a star of equal magnitude.

I did not want to sound as if diffraction is not taking place, it is, but the diffracted light around the true disk of the moons is too faint for us to see, it's as simple as that. The satellite itself can be seen, because it has enough true area that has a combined brightness enough for it to become visible.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: t.r.]
      #6283897 - 12/31/13 04:31 PM Attachment (10 downloads)

At the risk of confusing things further, I did a simulation in Mathematica (technical details below). It does show that EdZ is correct in that the diameter of the diffracted image of a disc is approximately equal to the Airy disc size plus the diameter of the extended object, if that object is relatively small like a moon. This makes sense logically (Edited - see third post below)

For the graphs, the x axis unit of 1 is the size of the Airy disk. The first graph is of a point source. The second is of an extended object approximately the size of the Airy disk (for simplicity). You can see that the second graph has a diameter of approximately twice that of the Airy disk, with a much smoother falloff. I used a Bessel function for the intensity of the point source. I produced an extended source by making a circle made of pixels, and calculated each point by summing the Bessel functions over the entire extended source. I only used a 10x10 graph because this sum took quite a while to calculate. I suspect that a larger graph would be smoother. The units of intensity may be off between the two graphs.

Edited by Derek Wong (12/31/13 04:47 PM)


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6283898 - 12/31/13 04:31 PM Attachment (9 downloads)

There are two effects we need to separate. First, there is diffraction, and second, there is blooming that occurs in CCD images or in one’s eye when we see bright objects. Bright stars are bigger because of this blooming and perhaps because their first diffraction ring smears into the image at low powers.

For Thomas, I think you are correct from an observing perspective. You can detect different sized moons in small scopes, it is just harder than in larger scopes. A very large scope will show Callisto as 1.3” and Ganymede as 1.4”, whereas an 80mm scope will show Ganymede as 3.2” and Callisto as 3.1” (EDITED: NOT according to the next post, sorry). I don’t know what effect it is, but I do agree that the moons look different sizes in smaller scopes. From your observing posts, you seem to use very high magnification and have a lot of patience, which is necessary to do such things (having a Zeiss scope doesn’t hurt ). EdZ post seems to agree with you. By the way, you can do infinite sums of infinitesimally small quantities, either through integration in calculus or through near-infinite sums for approximations.

TR, I think your explanation and the link are correct in that diffraction causes these effects. However, the use of the term “resolving” leads to some confusion. Whatever the effect is, we can see differences, so long as the seeing, optical quality, and vision of the observer are all good.

Edited by Derek Wong (12/31/13 05:41 PM)


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6283966 - 12/31/13 05:09 PM Attachment (25 downloads)

I must apologize to Thomas because I didn't even interpret my own graph correctly. I have attached a version that shows the entire plot range. This is of a moon the size of the Airy disc.

The green lines show the size of two Airy discs, and indeed the vast majority of the energy is inside these lines. However, if we look at the red lines, within the Airy disc size, most of the energy lies there. In fact, if we ignore the energy outside of the green lines, 88% of the energy is inside one Airy disc diameter. That may be why Thomas sees the moons as near their correct sizes.

I know a little math but I have no expertise in optics. The calculations were done off the cuff and could have errors. If someone can verify or dispute this, PLEASE chime in and give us the correct answer!

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6284154 - 12/31/13 06:29 PM

Thanks to Derek for his work. I'll comment more on it tomorrow. It is getting really late here and must go up early tomorrow.

I have been out for a couple of hours, observing Jupiter and his moons. The seeing was nowhere near as good as yesterday, but it had OK moments.

This time I did a comparison between the sizes of the satellites in my 85mm Zeiss, compared with the belts of Jupiter, and did the same thing with my 150mm refractor. There was no visible change in the relative sizes of the satellites or compared with the belts of Jupiter. They appeared the same in both scopes at approximately the same magnification, about 150x - 160x. Neither smaller, nor larger, compared to Jupiter.


Clear skies!
Thomas, Denmark

Edited by Astrojensen (12/31/13 06:30 PM)


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6284322 - 12/31/13 08:04 PM

The theory here seems sound. A smaller scope should show a realative larger diameter than a large one. In my 6" the moons appear as small discs with a sharpish edge and a fiant diffraction "area" plus a hint of a ring. In an 83mm, the moons look a little bigger to me, but more fuzzy edged (as would be expected). A friend and I talked about this very same topic about 30 years ago.

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Re: Jupiter in small refractor telescopes new [Re: bremms]
      #6284819 - 01/01/14 03:54 AM

I've never seen diffraction rings around the moons of Jupiter, though I've heard about others seeing them, which sound interesting and curious. I actually specifically looked for them yesterday with the 150mm, but didn't see them. My 85mm barely shows a hint of the first diffraction ring on even a third magnitude star, when it is in best focus, so it will not show so much as a trace of it on anything approaching 5th or 6th magnitude.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6284913 - 01/01/14 06:33 AM

Quote:

I've never seen diffraction rings around the moons of Jupiter,




There will be an explanation for this phenomenon?



Edited by STEEL (01/01/14 09:51 AM)


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6284919 - 01/01/14 06:38 AM

Hello Thomas and all,
thank you for your interesting discussion and about the moon size. I think fact is that it is possible to see different moon sizes with the 85 mm APO. The moon view is probably a little washed out by the resolution but I think it possible to guess/see better than diameter + resolution although even that wouldn't be bad.

In the chip industry we use 193 nm light and the structures are far smaller now (with several tricks). That does not prove things but it gives a hint that sometimes more is possible than you expect.

At least I think that Thomas statement is true that he can see what moon he is watching by the diameter and it's colour. What will be true, too that a bigger telescope with more resolution will make it easier to see/guess the real diameter.

I'll try to closer look on the Jupiter moons the next time and try to guess their diameter and what moon it is with different telescopes (I have a 114/900 Newton, a 80/1200 and 102/1100 achromat).

I think we should end the theoretical discussion now and should just tell/report what we see in small aperture refractor telescopes.
For a theoretical discussion we could open another thread.

Clear skies and a happy new year,
Roland


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Re: Jupiter in small refractor telescopes new [Re: STEEL]
      #6284930 - 01/01/14 06:53 AM

Quote:

Quote:

I've never seen diffraction rings around the moons of Jupiter,




There will be an explanation for this phenomenon?



Me, too, I haven't seen diffraction rings around the moons of Jupiter or around Jupiter.
Maybe the diffraction rings get's washed out by several diffractions rings around each point and if the star or the moon is small but too dark the diffraction ring area is too dark too... but that is just guessed.
As I said we should primary focus on observation reports of Jupiter maybe with photos and sketches.

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6284993 - 01/01/14 08:30 AM

Right, let's end the theory stuff now and just report observations. I'll try and write an article about resolving the moons.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6285411 - 01/01/14 12:06 PM

I did some more work and I think I have an explanation for some of the things in this thread, but since people don’t want to see more theory I’ll leave it for some other time. Briefly, Bremms has it right. There are no bright diffraction rings on these extended sources because they get averaged into the smear around the moon. Ganymede is only 42% of the Airy disk size of the 85mm scope, which shows a disc that isn’t much different than the Airy disk surrounded by extra light. Ganymede is 81% the size of the Airy disk of a 150mm scope. In the 150mm scope, it broadens the diffraction pattern quite a bit. The 150mm scope still shows a narrower peak than the 85mm but it is closer than we would think. One thing that is not answered is how big of a disc our eyes see when we convert these patterns into an image.

Getting back to the visual thread, I have a very sharp Nikon 65mm f/12 apo that I will try to use to distinguish the moons. It is difficult not to use the overall magnitude to guess which moons are which.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6285558 - 01/01/14 01:33 PM

Quote:

I have a very sharp Nikon 65mm f/12 apo that I will try to use to distinguish the moons. It is difficult not to use the overall magnitude to guess which moons are which.




Oooh! A Nikon 65mm apo! Those are very rare.

Yes, at lower magnifications, it's entirely possible (and hard not to) identify the moons from their different magnitudes and even colors. Io and Europa look very identical, though, and can be hard to tell apart.

I would be very interested in hearing what you may see at higher magnifications in the 150x - 200x range. I can use my 63mm Zeiss Telemator (achromat) and try do the same. Try noting how large the moons appear, compared to NEB and SEB. This will give a rough comparison value.

Do be aware that you *must* use enough magnification to allow your eyes to distinguish the true disk of the satellites, if it is visible. At 200x, Europa appears 3.3' in diameter, 1/10th the diameter of the Moon as seen with the naked eye. Io appears 4' across, Callisto 5.3' and Ganymede 5.7'. One might fear that would be too low to be detected, but the extremely small exit pupil and the accurate focus of the telescope essentially gives everyone's eyes 20/10 correction at the eyepiece. The disks are small, but clearly detectable.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6285649 - 01/01/14 02:27 PM

Hi Derek,
the theory is interesting, too. Maybe you can open a new thread about this
Quote:


There are no bright diffraction rings on these extended sources because they get averaged into the smear around the moon.




Something like that is probably true. You made me curious and so I tried to calculate the diameter of the moons and they should be about Io = 1,22", Europa = 1,05 ", Kallisto = 1,62 " and Ganymed = 1,77 " if Jupiter is 48 "...

Quote:


Getting back to the visual thread, I have a very sharp Nikon 65mm f/12 apo that I will try to use to distinguish the moons. It is difficult not to use the overall magnitude to guess which moons are which.




I'm curious to hear from your observation.

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6285651 - 01/01/14 02:28 PM

I did a little searching and found the thread I was referring to earlier. Turns out, you were at the center of that discussion as well Thomas. David Knisely agrees with EdZ and I have to agree with the two of them because the physics backs them. Here is a link to the relevant page, go down to David's post about the spurious disk, but the whole thread was an interesting read again...

Galilean Discs


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Re: Jupiter in small refractor telescopes new [Re: t.r.]
      #6285823 - 01/01/14 03:33 PM

Thanks, t.r. That saved me much work.

I am a bit sad I never got the opportunity to do the experiment with Mars. I will, if I can get the chance, try again. Currently, a 20mm aperture and 48x will make Mars appear the same relative size in the eyepiece as Ganymede in an 85mm at 200x, except it's a waxing gibbous. I can get 42x on my Zeiss Telemator with the Baader bino, 25mm Zeiss eyepieces and 1.25x GPC. That's the same as Ganymede at 170x.

It should be *very* interesting to see whether I can see the phase. The Rayleigh limit for a 20mm is right at 7"...

So, what's the bets? The biggest joker is the weather, obviously.


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes *DELETED* new [Re: Astrojensen]
      #6285833 - 01/01/14 03:41 PM

Post deleted by Eddgie

Edited by Eddgie (01/01/14 04:03 PM)


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6285868 - 01/01/14 03:55 PM

Quote:


Please forgive me if I missed this in the ongoing dialog. I only looked at the graphs and responded based on the fact they the auther treated the moons as point sources and that is a fundamental error.





Hi Eddgie, if you were referring to me as the author, I definitely did not make that fundamental error, although there may be minor errors of scale. Please read the entire text. The reason that the simulation took so long is that I broke up the discs (not points) into tiny pieces and calculated the sums of the diffraction patterns. The results are not as simple as just adding two numbers.

The previous thread just referenced gives a lot of information that I can use to check my calculations. After I do that, I am going to see if Vla of the telescopeoptics site thinks they are accurate.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6285883 - 01/01/14 04:04 PM

Please accept my apogies.

In the graph, it was not evident.

Again, a thousand apologies.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6285911 - 01/01/14 04:21 PM

Hi Eddgie:

No problem. I love these forums, but sometimes the format with one photo per post doesn't allow continuity. Since you seem to know a lot more about optics than I, I will run things by you as well.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6285924 - 01/01/14 04:30 PM

Hi Thomas:

Thanks for the tips on observing these things. Although the Moon takes a large amount of magnification with this little Nikon, Jupiter washes out as in any scope at 100x per inch. I have not thought about looking at the moons at such high power.

Sorry for bringing a bit of theory back :-) but there is a bit of an issue in comparing the size of a moon to a belt. A small aperture will enlarge both the moon and the apparent belt width via diffraction so the relative widths may look the same as in a larger scope. I think that this double enlargement may explain some of the things you are reporting. I still believe your observations, and I do think that the moon size effects that you are seeing are real, and that there is a way to reconcile everything with physics.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6285956 - 01/01/14 04:42 PM

After going back to the previous page, I realize that you convered the case for extended target well.

Again, apologies for not looking back at the previous page and mis-understanding your graph.

Was a nice writeup.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6286863 - 01/02/14 03:30 AM

Hello,
now we wrote about theory. Could you please sum up things from this discussion? Is it possible to see a bigger disk of the two larger moons? Is the expected moon size = moon diameter + resolution e.g. Ganymed_in_85mm = 1,77 " + 1,35 "? If that's true then it should be possible to see different sizes of the larger moons and maybe even see of the 2 smaller moons.
Clear skies,
Roland

Edited by Niklo (01/02/14 03:44 AM)


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6286875 - 01/02/14 03:58 AM

Here are my notes from tonight with a 65mm Nikon apo. The scope is extremely sharp and easily handles 100x/inch with a great star test and almost no color out of focus on Sirius. I had to work most of the night but was able to get out for two 30 minute sessions, concentrating on the moons. I observed first then looked up which moons they were. I have a decent amount of experience observing planets (not as much as many around here) but I have never spent any time observing moons that are not transiting with small scopes.

Approximately 4:30 UT 1/2/14:
Two moons were seen far from Jupiter’s disc. The inside moon was larger and more distinct (Ganymede); the outside moon was fuzzier and fainter (Callisto). The diameter of Ganymede’s disc was much less than the diameter of the NEB. Two moons were seen closer to the disc. The inside moon was smaller (Europa) and it was difficult to see its size due to the glare from the planet. It appeared slightly smaller than the outside moon (Io).

Approximately 8:30 UT 1/2/14:
The two far moons Ganymede and Callisto appeared the same as in the last description. The closer moons looked like they had switched places, and indeed Europa was now on the outside and Io on the inside. The moons had very slightly different colors but I haven’t spent enough time looking at them to recognize them. No diffraction rings were seen.

I did look at several stars of comparable brightness in Orion. In particular, there were two that were fairly close and about a magnitude apart in brightness. Their “spurious discs” looked like they were of equal width, less than the moons.

The conclusion is that I could differentiate Ganymede/Callisto and Europa/Io, whatever the reason.

There is not much backfocus on the scope, but I may be able to get it to focus with a binoviewer and a 2.6x magnifier. I’ll try that some other time. I wonder if binoviewing makes the discs slightly smaller because it reduces their surface brightness. I also want to try a Tak FC50. Several big scopes are grounded pending mount issues :-(

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6286881 - 01/02/14 04:04 AM

Marvellous observations, Derek, and a perfect match with my own. It is very telling that you could tell from the appearances of Io and Europa that they had switched places, before checking with software or litterature.

What star in Orion did you look at?


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6286886 - 01/02/14 04:08 AM

Hi Thomas:

I decided to take my contacts out, because I suspected that my new contacts were causing a bit of astigmatism. That meant I was blind as a bat, so I just pointed the scope to Orion, focused and started panning around :-) Sorry for the non-scientific approach.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6286900 - 01/02/14 04:20 AM

Haha! No problem. Doesn't the Nikon have a small finderscope? A 5x21 or something like that?


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6286961 - 01/02/14 06:26 AM

Hello,

I was observing and sketching Jupiter yesterday in 80mm refractors again:



Seeing was better than last time in 80mm and I could push magnification to 120x. I could detect the white-oval area in STB (although I could be biased here, since I know from the previous observations that it was there). The white spot was definitely there, but I'm not sure about the edge from the equatorial side. In any case, Jupiter looked very interesting in the small 80mm refractor.

Besides playing with an equipment (old Zeiss versus newer AS80, CZJ O-10 versus Delos 10), I was trying to judge sizes of Jupiter's moons. To my eyes, the size was correlated with brightness at 120x. I sorted the moons according their size and latter at home I identified which one is which. Here they are, starting from the smallest one: Europa, Callisto, Io, Ganymede. Io should be smaller than Callisto but I saw it larger, probably due to larger brightness.

Edited by Sasa (01/03/14 03:38 AM)


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6287034 - 01/02/14 08:10 AM

Hello Alex,
your sketches are quite similar to my photos and the view on the 15.12. Maybe the photo could be interesting

Your sketch is really quite good. Thank you.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6287522 - 01/02/14 12:38 PM

Quote:

Haha! No problem. Doesn't the Nikon have a small finderscope? A 5x21 or something like that?





Hi Thomas:

Yes, there is a small finderscope but we have so much light here from Los Angeles that I can't see 5th mag stars.

Back to the observations, Io and Callisto were too far apart for me to make a great comparison of their relative sizes. From Alex's post, it seems like that is the comparison I need to do.

Derek


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6287567 - 01/02/14 01:00 PM

Quote:

Hello,
now we wrote about theory. Could you please sum up things from this discussion? Is it possible to see a bigger disk of the two larger moons? Is the expected moon size = moon diameter + resolution e.g. Ganymed_in_85mm = 1,77 " + 1,35 "? If that's true then it should be possible to see different sizes of the larger moons and maybe even see of the 2 smaller moons.




Hi Roland:

The other thread had a lot of great info and referenced telescope-optics.net which referenced a Mahajan book that my University library had online :-) Briefly, things are quite interesting and a bit complicated. The graph I did looks like it matches their calculations. The following statements are for an aberration free system only; calculating an aberrated system is possible but more complicated. Moons whose diameter is 50% or less of the Airy disk size (as is the case with an 80mm scope and Ganymede) add a small amount to the width of the image. Moons whose diameter is 25% or less compared to the Airy disk (as with Europa and a 65mm scope) are only very slightly larger than a point source pattern and could show diffraction rings if the moons were brighter.

I will try to make sense of this and write this up but the bottom line is that there is probably a combination of brightness-induced enlargement as well as actual physical widening, and that seeing, the individual observer's brain processing and perhaps sky brightness may influence the disc size. I won't even start with optical quality on this forum :-)

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6287629 - 01/02/14 01:30 PM

Quote:

I won't even start with optical quality on this forum :-)




I think it's probably best to stay away from that rabbit hole!


Clear skies!
Thomas, Denmark


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6288079 - 01/02/14 04:53 PM

Hello Derek,
the 80 mm refractor should have about 1,45 to 1,5" resolution. So the airy disk should be about 1,5" and the moon Ganymed with 1,77" should be bigger than the airy disk, shouldn't it? So it should be possible to see a bigger disc than the smaller moons.
I checked my photos and Ganymed looked bigger than the other moons. Callisto seems darker but looked bigger, too (that's very difficult).

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6288467 - 01/02/14 08:49 PM

Quote:


the 80 mm refractor should have about 1,45 to 1,5" resolution. So the airy disk should be about 1,5" and the moon Ganymed with 1,77" should be bigger than the airy disk, shouldn't it? So it should be possible to see a bigger disc than the smaller moons.
I checked my photos and Ganymed looked bigger than the other moons. Callisto seems darker but looked bigger, too (that's very difficult).





Hi Roland:

Dawes limit for an 80mm scope is 1.45", but the width of the Airy disk is much more than that (3.43" at 546nm wavelength). If you go to this website http://www.rocketmime.com/astronomy/Telescope/ResolvingPower.html , you can measure yourself that the distance between the centers of the two stars in the middle left picture is much less than the diameter of the Airy discs.

The problem is that we don't perceive the entire Airy disk; we see only a portion of it. The amount that we see depends in part on the brightness of the source. Photos will differ from visual, unless they are exposed just right and they are filtered in a similar way to the human eye. See this thread for a lot of discussion:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5645468/page...

The thread says that 50-60% of the Airy disc size is the diameter of the disc we see in a 6th mag star and discusses some of the physical factors that may alter the perceived disc size. However, one thing I have learned from being in the human genetics field is that biology is very messy. Our brains may construct the discs differently, our lenses may absorb a lot of light depending on our age, visual acuity is different, etc. I am sure that people will see different disk sizes just as different people perceive different things when they look at the same optical illusion piece. Binocular viewing and monocular viewing complicate things even more.

The bottom line is that most people can clearly see that Ganymede is larger, but the devil is in the details and there will be arguments about the smaller moons. I will try to explain the physics portion when I have time to do some calculations, but it probably won't settle most of the arguments :-)

Derek


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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6288949 - 01/03/14 03:06 AM

Hi Derek,
ah, I see the problem. So for simulation you should do a convolution of the airy disk with the moon or planet disk.
It depends how much intensity is in the diffraction rings. The outer part of the result disk of the convolution should be much darker so it could be that the seen diameter of the moon is smaller than 3.43" + moon diameter and rather 1,5"+moon diameter if you take just the brightest part of the moon. Maybe we could measure it with a webcam. You can calculate how much arc seconds Jupiter in the moons move per second and then you can measure the diamter of the moons on the photo. That would be an interesting project

Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6289000 - 01/03/14 04:33 AM

In my, rather extreme view, the resolution of every lens is potentially 0.0". Let me explain this - if you take the image of two point stars separated by 0.1", the result would be different from a single star pattern. Even in 80mm lens. If you equipped it with CCD camera, it is just a question of time until you collect so much photons that you could clearly separate those two patterns. Since number of photons is just a measure of information, in my view, the resolution is just a matter of collected information. Every entrance pupil screws the information, the larger lenses have smaller diffraction patterns and they screw the information in lesser way. They also collect more photons. As a result, larger lenses reach better resolution when you have time constrains.

Eye cannot collect photons infinitely long. Also brain plays important role in processing the information. This explains various "resolution" limits from Dawes to Sparrow. The brighter the object is, more info you can collect and you can resolve stars well below Dawes limit.

For the Jupiter's moons, you can definitely calculate their patterns and compare them to the point source pattern. But the next step you need to do is to estimate number of photons your eye can realistically collect within it's integration time, i.e. estimate if the eye can collect enough information to separate those patterns. It can be done using statistical methods and it should give a first order estimate if the two things are distinguishable. The result of these calculations would be a sentence like: "Io's pattern can be distinguished from point source pattern in 3% of time, in 80mm telescope with 0.1s integration time and 5% quantum efficiency of the detector." There is probably nothing more you can say at the end. Of course, I totally made out those 3%. If the result would be in 10% range and below, I would say it is probably indistinguishable, if it is in 50+% range, it might be possible.

But then brain enters the game. It is a clever device, if trained. It can increase integration time to few seconds, it can correlate information in time, it can bin several light cells together, and who knows what other tricks it is using in order to push the limits for faint objects... These things can easily make several magnitude difference in what are the faintest stars people can detect. I have no idea what can the brain do in terms of resolution but I'm sure it has many tricks in its sleeves.


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6289050 - 01/03/14 05:45 AM

Hi Alex,
I think 0.0" resolution is not correct but sometimes you can go beyond the normal resolution e.g. see chip industry.
I can try to measure the visible moon diameter with webcam and look how is the diameter captured by the webcam. Then we can compare the webcam image and look how it looks in the eye piece with our brain eyes combination.
One of the problems is that we have cloudy nights now in Germany ...
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6289062 - 01/03/14 06:11 AM

Hello Roland,

of course 0.0" was a little bit of exaggeration, just to make my point. I wanted to demonstrate, that term "resolve something" is vague and that you can resolve with 80mm lens whatever small distance you want as I described in this gedunk experiment. You just need more time (actually way more time).

At the very bottom, the think that drives what can be resolved is amount of photons you collect. This is due to statistical nature of incoming light. You simply can't do better then this, even with ideal device. Of course, in real life thinks could be much worse.


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6289159 - 01/03/14 08:14 AM

I just made a quick estimate what is the absolute limit for ideal sensor with 5% QE. The device will collect about 5000 photons in 0.1s from 5th magnitude Io. From my calculation, it should be enough to detect with almost 100% certainty about 5% relative changes between two objects.

For comparison, 1.7" source (Ganymede) will have about 20% larger spot size than point source, so it should be doable. Europa, 1.0" source, should have about 7% larger size than the point source and it is on the limit of what is doable with ideal device under ideal conditions (no atmosphere).

For this purpose, the spot size diameters were calculated from an average of squared distance of photon hits from the center. This is definitely not what eye is doing (but it was easy to implement), reality will be definitely worse - eye is probably trying to find sharp edges which will have higher statistical fluctuations. I also did not use Airy formula with Bessel functions but approximate with Gaussian function (should be more than enough for this purposes).


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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6289285 - 01/03/14 10:03 AM

Hi Alex,
thank you for your answers. Currently it's too much theory for me Maybe we should come back to write about Jupiter view reports and pictures and I try to watch the moons the next time.
Clear skies,
Roland


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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6292942 - 01/04/14 11:02 PM Attachment (7 downloads)

Quote:

I've never seen diffraction rings around the moons of Jupiter, though I've heard about others seeing them, which sound interesting and curious. I actually specifically looked for them yesterday with the 150mm, but didn't see them. My 85mm barely shows a hint of the first diffraction ring on even a third magnitude star, when it is in best focus, so it will not show so much as a trace of it on anything approaching 5th or 6th magnitude.


Clear skies!
Thomas, Denmark




Thomas, I see them quite easily as very bright rings. But in anything less than Ant II seeing, they disappear. So surely at least good seeing is required, much like a star I'd imagine. My scope is also obstructed with a slight amount of SA, so there is sufficient energy in the rings for them to show. That's probably key, having sufficient energy in the first ring due to aberration and/or obstruction and then observing in descent seeing.

I trust the topic below in on topic as it describes what can be seen with Jupiter and it's moons, specifically.

It's interesting to note that only a point source produces a true Airy disc of size 138.4/Dmm in radius. If a moon is larger than that, it produces an expanded PSF that gradually becomes larger than 1.22 Lambda/D. Of course this begins to delve into the difference between the Airy disc (which is not entirely visible) to the visible spurious disc which is visible.

There is empirical evidence, in double star observing, indicating Raleigh is not the limit for resolution. Very tight doubles can be split by experienced observers (present company included) down to about half the Raleigh limit and slightly less. So, a 100mm refractor should put a slightly elongated Airy disc of a tight double on the focal plane down to about 0.7" arc. This is much smaller than the Airy disc so you are 'resolving' (using the term loosely) images smaller that the Airy disc by a bunch.

Remember, the Airy disc diameter, which supposedly covers everything smaller than itself making smaller detail invisible, is 2.6" arc in diameter. Yet, you can resolve to about half Raleigh. Folks do it all the time. My personal best is just less than 0.5 x Raleigh on (Chi Aql), but I get to cheat a little being obstructed as an obstructed Raleigh limit, thus the Airy disc, is about 10% smaller. My best is actually closer to 0.6R for an obstructed scope.

So, at half the Raleigh limit we are actually observing at 1/4th the Airy disc diameter. In fact, an object with a diameter of 1/4th the Airy disc is just about the point of defining a true point source that produces an Airy disc radius of 1.22 Lambda. At this diameter, the PSF is only very slightly expanded at FWHM, which approximates both Dawes and the spurious disc radius, and for all intents and purposes is a point source PSF.

Anything larger begins to expand the PSF at FWHM and once the object is the diameter of the Airy disc the PSF is expanded markedly (see below.) Somewhere in this range the object on the focal plane is becoming an extended object depending on how it's defined.

So, on an object the size of the Airy disc, one should be able to resolve detail down to about 1/4 Airy disc diameter or half the Raleigh limit. Ganymede in a 6" is a perfect example, it is the roughly same diameter of the Airy disc and can show Osiris quite easily in diffraction limited seeing. I've seen it, and maybe a hint of Galileo Regio, too.

Here at these small spacial frequencies in diffraction limited seeing (about 8/10 Pickering) obstructed scopes come into their own as shown on the MTF where obstructed scopes exceed even perfect unobstructed apertures. Seeing is believing and very much required. Refractors lag a tiny bit, but the principles are the same.

So, to sum up. A true point source PSF we observe on the focal plane after diffraction begins when the object diameter is 1/4th the Airy disc diameter, half the Raleigh limit, or smaller. Anything larger becomes a 'disc' or at least an expanded point source (PSF.) As the object get's larger and it's PSF expands, you can begin to resolve detail at about half the Raleigh limit for both very close point source double stars and extended objects. Of course, at these high spatial frequencies, object contrast must be very high to begin with just like a double star point source. But, anything larger than 1/4th the Airy disc diameter should begin to define what is a point source and what is a very small disc seen as an expanded PSF, physiological effects aside.

There are two sources, one here (graph below) and the other is my own experience in diffraction limited seeing. Since diffraction limited seeing for long periods of time is about as close to lab-like conditions as we can get in the real world, I believe theory is pretty darn good at explaining what we CAN see and having seen it myself.

So, each moon in a small refractor is very likely to be a true(?) disc as long as the moon's apparent diameter exceeds 1/4 Airy disc diameter for that aperture.

Thomas, I trust your ball bearing experiment, but will leave interpretation of the above to you. I wonder how nicely the ideas above and your experiment dove tail.

Edited by Asbytec (01/04/14 11:22 PM)


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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6292983 - 01/04/14 11:31 PM

I also see diffraction ring in Jupiter moons.

I just went out to take a quick at Jupiter and its moon at 107x with 60mm f/16 and 89x with 50mm f/6.6 refractors.

I see the ring in Jupiter moons. Seeing is ok, below average.

Tammy


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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6293007 - 01/04/14 11:42 PM

Quote:

Hello Derek,
the 80 mm refractor should have about 1,45 to 1,5" resolution. So the airy disk should be about 1,5" and the moon Ganymed with 1,77" should be bigger than the airy disk, shouldn't it? So it should be possible to see a bigger disc than the smaller moons.
I checked my photos and Ganymed looked bigger than the other moons. Callisto seems darker but looked bigger, too (that's very difficult).

Clear skies,
Roland




Dawes resolution is not really representative here when you split hairs as to when or when not a disc is a resolved disc. Its close but off.

With my 70mm I have seen the dirt looking little dimmer but big Callisto next to Ganymede and its a little uncanny. Yes there is the magnitude difference to understand here but there seemed something odd about Callisto . If it were dimmer well its seem dimmer and so be it - done. But its not that simple - it appeared large still - but strangely ashen and dimmed but not shrunk. Through my 8" its a handedly easy call and Callisto appears chocolate - umber while Ganymede is a subtle cream gold. With the 70 - its not a dimmer tinier "star" its a moon still - just toned greyish.

There's a quasi resolution it would seem that's taking place in small refractors . One foot in stellar diffraction patterning and the other in the emergence of a true disc - if incomplete.

Compelling stuff for a small refractor.

Alex- that's tremendous work!!!!! I'm very impressed you've got some serious details down very well!



Pete

Edited by azure1961p (01/05/14 06:03 PM)


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Re: Jupiter in small refractor telescopes new [Re: azure1961p]
      #6293052 - 01/05/14 12:12 AM

I was so pleased with my SV ED80 last night - watching Io move in to "kiss" theface of the Jupiter, before disappearing behind it, and then seeing the distinct shadow of Ganymede as it transited across the face from the other side.


Astonishing the fun you can have with an 80 mm!


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: dvb]
      #6294065 - 01/05/14 02:42 PM

Hi,
today is Jupiter opposition, so it could be interesting to watch Jupiter today. By the way Ganymed has a good distance so it could be a chance to see it with naked eyes if you shadow the bright Jupiter.
Clear skies,
Roland


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azure1961p
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Re: Jupiter in small refractor telescopes new [Re: dvb]
      #6294447 - 01/05/14 05:35 PM

Quote:

I was so pleased with my SV ED80 last night - watching Io move in to "kiss" theface of the Jupiter, before disappearing behind it, and then seeing the distinct shadow of Ganymede as it transited across the face from the other side.


Astonishing the fun you can have with an 80 mm!




There's something very captivating about seeing a Galilean moon close the gap between itself and Joves limb. Then there's that moment its so utterly tight you can't tell if its touching or not - and a nice quality refractor can make it breathtakingly beautiful.

Pete


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azure1961p
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Re: Jupiter in small refractor telescopes new [Re: azure1961p]
      #6294470 - 01/05/14 05:45 PM

Norme,

M familiar with the models and examples you cite from previous discussions though it would seem with respect to Ganymede you had recorded spots perhaps 0.5R - you recall Oriris was seen as a small starry spot perhaps .35-.40 arc seconds in diameter and a similar spot opposite this on Ganymedes other limb. True in that Ganymede rendering you show Galilleo Regio as a generalized shading but far smaller you have Osiris a d it would seem to agree with 0.5R.

What say you?

Pete


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Asbytec
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Re: Jupiter in small refractor telescopes new [Re: azure1961p]
      #6295142 - 01/06/14 12:18 AM Attachment (32 downloads)

Yea, Pete, I say as you say. A 6" can resolve features in Ganymede as long as the optic is the limiting factor (seeing being diffraction limited for long enough to catch it.) Ganymede is the same approximate diameter of a 6" Airy disc, so we are resolving detail smaller than the the Airy disc.

Here's the kicker. It's absolutely true the diameter of spurious disc (not the Airy disc) is the smallest feature you can see in any aperture. Yet, you can see objects that are four times smaller.

We can do so because of the effect on the PSF. Only a true point source creates a true Airy disc while the spurious disc is somewhat dependent on magnitude. (See Wilfried's work attached in the double star forum.) An optical point is defined at about 1/4 the Airy disc diameter, either an extended object at this angular diameter or two stars with this angular separation.

Anything larger than 1/4 Airy diameter begins to expand the PSF and we can begin to notice it. If the object diameter is large enough that it is no longer a point source and it has a high contrast feature on it that is a point source, you can see that point feature superimposed on the expanded PSF 'disc' of the former.

Apply that to whatever aperture, pray for great seeing, and you're off and running.

Edit: Reading back, Derek seems to explain this well.

Edited by Asbytec (01/06/14 11:34 AM)


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Mark Harry
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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6295867 - 01/06/14 12:33 PM

My own research, if the object is a LINEAR feature, you can detect it a lot smaller than airy disc, perhaps 10-15x smaller; or more.
M.


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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6296134 - 01/06/14 02:34 PM

Quote:

My own research, if the object is a LINEAR feature, you can detect it a lot smaller than airy disc, perhaps 10-15x smaller; or more.




This agrees with research and experiments done by Barnard and Pickering, as well as myself.


Clear skies!
Thomas, Denmark


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Asbytec
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6296835 - 01/06/14 08:17 PM

Does that include bright linear features, as well? It should.

It seems resolving detail is all about contrast. You should be able to detect a bright point source sized feature on Jupiter if it has enough contrast, not unlike a dim star near the limiting magnitude against a dark sky. So, it's not so much about the size of the object as it is about it's contrast, though the size of an object dictates the contrast required to resolve it. The smaller it is, the higher the contrast has to be.

Detail is also about being able to distinguish between hues. If you notice white, you can see that Jupiter is mainly not white. Once you separate white from not white (possibly a soft gray) then that feature is resolved as well. Color perception and resolution daisy chain from white. Once you see white, it's easy to recognize grey. Once you see grey, you realize other belts, zones, or features are not exactly grey. They are a slightly different hue. Jupiter explodes with detail once faint differences in hue are recognized.


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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6297556 - 01/07/14 08:28 AM

During my investigation of linear detection, I happened to see a high contrast image of a spiderweb at around 50 yards/meters away with just my eye and assumed a 2-3mm pupil size. Translated to a telescope with good optics and high PSF, the capability should be quite respectable with high contrast objects.
*********
There is a television ad that starts out about the marvelous capability of an eye having the capability of seeing a lit match at 10 miles distance in the dark. (essentially a point source) I find this concept amazing, if true! But I haven't verified it personally. Right now, it's hard to keep a match lit anywhere outside!
M.


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Asbytec
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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6298830 - 01/07/14 08:33 PM

Mark, sure, this is where refractors rule. There is more energy in the central disc improving contrast. That same feature would likely be a bit more difficult in an obstructed scope of the same aperture. It could still be seen in most cases, just less easy as the peak brightness of the web falls with peak intensity and with respect to the background.

It's pertinent because Jupiter is full of nearly linear rifts, not unlike spider webs, whose detection does not depend entirely on Dawes or Raleigh limits of angular size. This is true even for point sources, though the apparent angular size of that point source would obey those limits. It can still be seen no matter how small provided contrast is high enough and refractors provide the best contrast.

When we scrap size requirements, the possibilities seem to become limitless. A four inch scope could easily resolve small white ovals if they are set off sufficiently. They may not resolve two white ovals very close together, but they can potentially see something there and maybe some elongation of two unresolved ovals (or two parallel bright/dark very thin linear features.)

Of course seeing plays a major role, however, in transferring final contrast to the focal plane.


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Derek Wong
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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6299273 - 01/08/14 02:11 AM

Quote:

Anything larger than 1/4 Airy diameter begins to expand the PSF and we can begin to notice it. If the object diameter is large enough that it is no longer a point source and it has a high contrast feature on it that is a point source, you can see that point feature superimposed on the expanded PSF 'disc' of the former.

Apply that to whatever aperture, pray for great seeing, and you're off and running.

Edit: Reading back, Derek seems to explain this well.




Hi Norme:

As helpful as that graph is, there is more to it that I don't understand. Perhaps it is because the graph is only for a perfect unobstructed system. I want to do a calculation for an aberrated system to see if the small moon pattern still matches the a point source.

If I step outside in the bright city, prior to dark adaptation my pupil should be 3-4mm max. The Airy disk size is somewhere in the 34-46 arc second range, yet small planets of 9-10 arc second diameter still don't twinkle much. Why is that? The Strehl of the eye is low even at 3-4mm, so perhaps the extra light is distributed differently?

Derek


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Asbytec
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Re: Jupiter in small refractor telescopes new [Re: Derek Wong]
      #6299416 - 01/08/14 07:12 AM

Hi Derek, I'd love to see your calculations. I suspect any aberration at modest levels won't affect the spurious disc much. Aberrations tend to throw light into the rings, and of course this affects the Airy disc to some extent. The disc might be a little less defined, a tad smaller, and a little less bright. So, unless the aberration is severe, one might imagine the moon's disc would be approximately the same.

Interesting question about the Eye's Strehl and any affect on twinkling. If you find out, then we'll both know.

I've always assumed the conventional wisdom about point sources twinkling and planets not due to their angular size, however small, with regards to the atmosphere. However, the eye is a small refractor and should be resistant to seeing. In fact it probably is, but twinkling is less seeing as we know it and more scintillation. Ya?

Staying on topic, Jupiter doesn't twinkle in small refractor telescopes, including the eye. Does it?


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vismundcygnus
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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6301180 - 01/09/14 12:22 AM

Last week I had a nice view of Jupiter with my Tasco 6TE-5 50mm...brown bands and creamy white, very nice. When I have observed other times the bands seemed darker. I missed the transit tonight, too cloudy.

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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6306169 - 01/11/14 12:53 PM

One sketch from even smaller refractor (63mm Telementor)



Some details are still visible but it is much more difficult to dig them out.


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christheman200
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Re: Jupiter in small refractor telescopes new [Re: Sasa]
      #6306537 - 01/11/14 04:29 PM

:O I'm amazed you can pull that out of a 60mm refractor!
I've been using mine recently because of it's quick set up and take down times in the cold, but my max magnification is around 30 times. I rarely get anything close to your sketch out of my 12"!


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hardwarezone
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Re: Jupiter in small refractor telescopes new [Re: christheman200]
      #6307730 - 01/12/14 09:42 AM

I was able to see 2 moons of Jupiter at 12x magnification on my st-80 last night.

Astigmatism in my eyes coupled with using the scope at high angle straight through made Jupiter appear to have 2 band aid shaped cross. I get the same ghosts images when looking up at the bright Moon.


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Eddgie
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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6307862 - 01/12/14 10:46 AM

Telescope performance is all about linear resolving power and contrast tranfer.

Linear resolution is independent of aperture. It is 100% a function of focal ratio and focal ratio alone.

All f/10 telescopes for example, regardless of apeture, have a linear resolutin of about 182 lines per millimeter at the focal plane.

All f/5 telescoeps, again, regardless of aperture, have a linear resolution of twice this, or about 364 line pair per millimeter at the focal plane.

Modulation Transfer Function (MTF) is used to describe how much contrast a particular width line will remain at the focal plane.

And even if there is an obstruction, optical issues, or even chromatic aberration (which often lowers contrast as much or more than a central obstruction will), once you get to line widths near the limit of what the scope can resolve, almost all instruments of the same apetuer will resolve lines pretty much the same, but this is because near the limit for the apeture, the contrast transfer has fallen to almost nothing.


Again, linear resolving power in lines per millimeter at the focal plane is 100% a function focal ratio (and wavelength I sould say), and is independent of apeture.

Ah, the question that is going to be asked: "Ed, if a 4" f/10 scope has all of the linear resolution of an 8" f/10 scope, why would I want the F/10 scope?"

Because while the 4" f/10 scope can resolve the same number of line pairs as the 8" f/10 scope can, when you look at Jupiter, with a given eyepeice, all detail will be shown at twice the size as in the 4" scope. Any detail will be shown at half the frequency.

Linear resolution though is the way MTF charts describe contrast transfer... How much contrast a given with line looses at the focal plane.

Can also be expressed as the maximum spatial frequency, and you can tell how wide in arc seconds a given sized line would have to be to be resolved at the focal plane.

Angular resolution is related to linear resolution, but it is realtivly unaffected by issues like CA, optical quality, or obstruction. Contrast transfer is used to describe how "Sharp" the opitcs are. Even a poor telescope will show an Airy Disk.


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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6308265 - 01/12/14 02:21 PM

How do you think my SW 70/500 would do on Jupiter ? I'm using a 10mm super plossl and also have RGBY filters and 2x 3x barlows. So 100 and 150x. Can i see more detail at 100 ( good seeing ) other than the 2 main bands ? How about the 150x ... will it be useless on 70mm ?

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Eddgie
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Re: Jupiter in small refractor telescopes new [Re: Mars Boy]
      #6308534 - 01/12/14 04:30 PM

I can't answer any of that from experience. I have never looked through a 70mm anything.

The more clear aperture you use, the better your chances of seeing more detail.

But 70mm should show you more than just the major equatorial bands I would think. You should be able to see GRS at 100x. Maybe shadow transits, and perhaps a hint of structure in the bands.

But if you have the telecope, why not point it at Jupiter and see for yourself?

I think 150x is to ambitious though. My advice would be try 110x. Past this and the image is going to get might dim.

But at 120x, I can see all of the features mentioned above using a 110mm telescope so I think you may be able to see quite a lot.


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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6308577 - 01/12/14 04:49 PM

Had a chance to compare my 85mm f/19 Zeiss apo with my 80mm f/15 Vixen GP 80L achromat in so-so seeing. Well, it was quickly over. The 85mm smoked the 80mm achromat big time. Just like I remembered it doing last time I did a comparison between them.

The Vixen is a much smaller and much lighter instrument, so difference in setting them up is hugely in its favor, with the 85mm being quite a beast. The reward is the sublimely fine images in the Zeiss.

I'll do a comparison again another night with better seeing.


Clear skies!
Thomas, Denmark


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azure1961p
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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6308695 - 01/12/14 05:26 PM

Quote:

I can't answer any of that from experience. I have never looked through a 70mm anything.

The more clear aperture you use, the better your chances of seeing more detail.

But 70mm should show you more than just the major equatorial bands I would think. You should be able to see GRS at 100x. Maybe shadow transits, and perhaps a hint of structure in the bands.

But if you have the telecope, why not point it at Jupiter and see for yourself?

I think 150x is to ambitious though. My advice would be try 110x. Past this and the image is going to get might dim.

But at 120x, I can see all of the features mentioned above using a 110mm telescope so I think you may be able to see quite a lot.




Depending on seeing a 70mm of its good, ought to allow 100x to 130x on Jupiter. The color isn't going to be there like larger aperture with the belts appearing a greyish brown a more grey than brown. Red browns are very difficult. The irregularities in belt edges show soon enough upon examination and barges given enough size, show well too. Festoons are seen but it also depends what jupiters putting up here in the way of that. Several years ago the EZ was merely frothy white with hints of mottled tonalities and that was it. Other times, nicely seen sweeping structures.
Alas details that show wonderfully intricate in medium and larger apertures will tend to appear smoothed and blocky even. Still, it never ceases to amaze me what 70mm will do under fairly good sky's and concentrated effort. There's a lot to be said for a very proper image despite angular resutuon approaching 2"! If my Ranger had mediocre to junk optics Id lose patience and interest quick with planetary and lunar with the scope. Because everything's so perfect looking - it brings out the competitor in me and I enjoy reaching for things normally the realm of larger scopes. Res is res but the way its served is a beautiful thing!

Pete


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6309509 - 01/13/14 02:44 AM

Hi Thomas,
that was expected that a 85 mm apo shows more than a 80 mm achromat. More interesting would be how close does the 80 mm f/15 achromat come to the 85 mm or 80 mm apo. What is similar what is different? What details were possible in each telescope? How does things change if you use just 80 mm aperture or both telescopes with 76 mm aperture.

Clear skies,
Roland


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stanislas-jean
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6309516 - 01/13/14 02:54 AM Attachment (29 downloads)

I did this comparison for 100mm. It is just significative of quality level difference, not by the coloring but by the optical acuracy in terms of PTV or L/xxx.
Stanislas-Jean


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Astrojensen
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6309558 - 01/13/14 04:53 AM

Quote:

that was expected that a 85 mm apo shows more than a 80 mm achromat. More interesting would be how close does the 80 mm f/15 achromat come to the 85 mm or 80 mm apo. What is similar what is different? What details were possible in each telescope? How does things change if you use just 80 mm aperture or both telescopes with 76 mm aperture.




Well, it almost flat out obliterated the 80mm at higher magnifications. Particularly on the Moon, but also on Jupiter. It was as if the 85mm was in an entirely different aperture class altogether.

However, the seeing wasn't perfect at all, so it'll be interesting and valuable to reexamine the situation in better seeing and with more time available.

Some things were immediately apparent, though: The color correction of the 85mm is far ahead of the 80mm achromat, even if the 80mm really doesn't show much color, with only a very dim, blue glow around Jupiter. It was also apparent that the 85mm has a much better wavefront accuracy, as the image was much crisper at higher magnifications and seemed to cut through the seeing a lot better. I couldn't get the magnifications matched as well as I wanted, but I could get the 85mm to 80x and the 80mm to 79x and spend some time with each image, trying to notice the similarities and differences.

The major difference was the overall color of Jupiter. It was very much yellower in the achromat than in the apo, with the 85mm showing it a whitish creamy yellow, while the disk was almost lemon yellow in the achromat. The belts were an odd brownish-purplish-reddish hue in the achromat, while they were ruddy brown in the apo. The festoons in the equatorial zone were blue-gray in both scopes. Both scopes showed a nice picture at 80x, but the details were slightly more abundant and more certain in the apo and the festoons in particular were only fleetingly visible in the achro, while being more certain (if still vague and ill-defined) in the apo.

I tried ~120x once in the 80mm, but the image was very fuzzy and hard to focus. This may have been due to the seeing, so I'll have to try again another night. On the other hand, the 85mm did pretty well at 105x even in the mediocre seeing and can hold up at 160x in very good seeing, even if the image gets very dim and sort of grainy, due to lack of light.

Bottom line: If I hadn't had the 85mm, I'd probably been really happy with the performance of the 80mm. But since I've got the 85mm, and it doesn't take all that much extra effort to set up, it's very hard for me to see why I should take the 80mm out. I may have felt differently, if it was a 100mm f/12. My 150mm f/8, stopped down to 112mm f/10.7 shows a lot more details on Jupiter than the 85mm apo, even if there's a lot more false color than in even the 80mm achro.

Last, I'll provide a couple of links to the Danish astro-forum.dk, showing some images of Jupiter, taken with a 100mm f/5 Sky-Watcher achromat(!) and a 90mm WO apochromat.

The 100mm f/5 achromat: http://astro-forum.dk/forum_posts.asp?TID=11615

The 90mm WO apo: http://astro-forum.dk/forum_posts.asp?TID=11599

Notice the differences in color of the disk of Jupiter and the belts. I see roughly the same differences in color between my achromat and my apochromat.

I may try stopping my scopes down sometime and try to see if it makes any difference. I've already compared the 85mm apo, stopped down to 75mm, to a TeleVue 76mm f/6.3 and the old Zeiss just obliterated the poor TeleVue on Mars and Saturn. Interestingly, the 80mm achromat also outperformed the TeleVue on the Moon and planets, despite the false color. The image was always much steadier and sharper.


Clear skies!
Thomas, Denmark


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Mark Harry
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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6309598 - 01/13/14 06:26 AM

Well then, why does an aperture mask shrink the size of spotplots in a refractor at the focal plane? I can provide plots of an 8" refractor I'm working on, and when apertured to either 5" or 3.5" at the image plane; and same image scale. The difference is very obvious. Reflectors, your postulation may hold water, but refractors, absolutely not.
Angular (disc) resolution seems to take a back seat (very far away) to linear rez. I attribute this more to eye response, and is highly dependent on acuity of the viewer.
As to poor telescopes showing the airy disc-
Due to my 'talent' of improving optics, a lot of poor specimens have been here for testing/evaluation.
-NEVER-, and I mean never; have I seen a -POOR- scope or optic show a disc! Fuzzy indistinct blobs, yes. Discs, no. This statement is made from direct observation, and not theory. (applies to all types of scopes)
And if I wanted an image twice as large as a 4" F/10, I'd choose an 8"- which I think is what you meant?
One last item- Line pairs/mm- I think you are way too optimistic. The same refractor I mentioned above is already down to only 40% contrast transfer at around 20 line pairs/mm. Tack on varying acuity issues... I think you can get the true picture without my posting a book
Cheers and no offense
M.


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Re: Jupiter in small refractor telescopes new [Re: Mark Harry]
      #6309602 - 01/13/14 06:36 AM

I had a chance to use my 80x700 this morning. I used a 12mm Ortho, and got a fairly good look at a few festoon features in the 2 main belts, and some grayish-olive polar areas. I was suprised that I could see this much at a bit less than 60x and using a 45 degree erecting diagonal!
At least the wind wasn't howling like it was yesterday!
M.


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Mars Boy
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6309616 - 01/13/14 06:55 AM

First of all thanks Eddgie and Pete. Well if i nail the GRS i will be a happy camper to be honest . The weather here in Bucharest is quite remarkable ( all time record temps for january ) so i will go sometime to get the gas giant.

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Asbytec
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Re: Jupiter in small refractor telescopes new [Re: Mars Boy]
      #6309758 - 01/13/14 08:48 AM

Quote:

Because while the 4" f/10 scope can resolve the same number of line pairs as the 8" f/10 scope can, when you look at Jupiter, with a given eyepiece, all detail will be shown at twice the size as in the 4" scope. Any detail will be shown at half the frequency.



Ed, this is one of those concepts I understand for about 10 minutes.

What I think you're saying is at the same exit pupil in both apertures at f/10? This is where the Airy discs in both apertures are the same linear size despite one being half (or twice) the angular diameter of the other.

At the same exit pupil, it requires twice the magnification to bring the 8" aperture's Airy disc to the size of the 4" scope. So, you can see the Airy disc (depending on visual acuity) at about 25x/inch which means about 100x in the 4" with the larger Airy disc and about 200x in the 8" with the half smaller Airy disc. This is the basis for the "optimum" magnification for viewing Jupiter. At higher magnifications, I suppose, no further resolution is gained nor contrast lost, the image is just dimmer. Is that correct?

The end result is, Jupiter is smaller in the 4" f/10 with a "given (10mm) eyepiece" because it's magnified only 100 times. And since it's Airy discs are larger, it has about half the resolution while the 8" f/10 provides a larger image (at the same brightness) and better resolution. Even though the Airy discs are both the same linear diameter at those magnifications, the 8" image is twice as large and can have twice as many strewn across Jupiter's diameter. Right?

Man, it's easier to think in terms of exit pupil than lines per mm. So, in 10 minutes, the exit pupil will still make sense, but lines per mm will fade from memory, again.


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Eddgie
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Re: Jupiter in small refractor telescopes new [Re: Asbytec]
      #6309867 - 01/13/14 09:50 AM

Oh, it seems horrible to think in terms of lines per millimeter at the focal plane, but at the same time, it is easier to envision what 100 line pairs per millimeter would look like for the avereage person than what a given size angle would be. So as horrible as it is, in fact, it just makes it easier to grasp.

How do you envision this? Well, here was my breakthough.

My breakthough occurred when I started using a virtual eyepeice with a 1mm field stop. Power or scope or nothing else matters other than the resolving power in line pair per millimeter at the focal plane.

If I put an 10" f/5 scope and a 10" f/10 scope next to one another, and I put a test card down range, I find that in the f/10 scope, the lines all run togehter when there are 182 displayed across the one millimeter field stop.

When I do this for the f/5 scope, the lines blur together when the card is the same distance away and there are 364 lines displayed.

Ah, but now, when I point the scope at Jupiter, using the same eyepeice, the f/10 scope shows it as being twice as large. So, while the f/5 scope resolves more lines, for a given eyepeice, I am using half the power.

If I put in an eyepice with a .5mm field stop on my test range, I see the same number of lines (182mm) and the same magnifcation, so while they have different linear resolution, in practical terms, they both behave the same way when the same power is used if they are the same apture.

But what if they are different apetures.

Say they are both f/10, but one is 5" and one is 10".

Now, when I use my card, what I find is that with my 1mm field stop eyepeice, I keep moving the card away in the 5" f/10 until I see 182 lines, at which point they merge to gray.

Ah, but when I use the 10" f/10 scope, for this to happen, I will have to move the card twice as far away because while the linear resolution is the same (182 lines per millimeter at the focal plane), the focal ratio (and hence the magnification when the same eyepecie with one millimeter field stop is used) is twice as much.

Now, I look at Jupiter. With the same eyepeice, I see Jupiter as twice as large in the 10" scope. If I could superimpose it on the grated lines of my test card, I would see that it covers half as many lines in the 10" f/10 scope as in the 5" f/10 scope. So, this means that every detail is seen at half the frequency in the 10" scope. Even though both scopes can resolve the same 182 lines, the bigger aperture does this at twice the distacnce to the test card due to its longer focal length.

So, using linear resolution seems funny, but it is easy to conceptuulize using a virtual eyepiece with a 1mm field stop, and imaginging how it would behave with test cards, and then by pointing it to the sky.


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: Astrojensen]
      #6310196 - 01/13/14 12:34 PM

Hi Thomas,
thank you for your comparison. The strange thing is that the only time I compared the 4" f/11 and the Vixen 80L it showed quite the same details with a better CA correction in the Vixen 80L but the seeing was bad that day so the 4" could probably show more details.
Last time I watched Jupiter with 133x in the Vixen 80L and the view was quite sharp. Even 150x was possible but I preferred the 9 mm ortho over the 8 mm planetary eye piece.

The colour of the Jupiter bands look different from day to day.
Bands a little more reddish:


Another day more brown:


I'll try to watch both with my 4" and my Vixen 80L and will report. If the time is enough I'll compare with my Bresser 114/900, too.

Clear skies,
Roland

Edited by Niklo (01/13/14 12:42 PM)


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Asbytec
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Re: Jupiter in small refractor telescopes new [Re: Eddgie]
      #6310210 - 01/13/14 12:43 PM

Thanks, Ed, I am gonna have to read that a dozen times. My fault, not yours.

Yea, I get the jist, then loose it after 10 minutes. Need one of those epiphany moments, I guess. I dunno, exit pupil seems so much easier. Let me mull it over, maybe it'll finally click.


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Niklo
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Re: Jupiter in small refractor telescopes new [Re: stanislas-jean]
      #6310228 - 01/13/14 12:56 PM

Quote:

I did this comparison for 100mm. It is just significative of quality level difference, not by the coloring but by the optical acuracy in terms of PTV or L/xxx.
Stanislas-Jean



Hi Stanislas-Jean,
thank you for your scetches. You draw many details on the scetches but for me it's difficult to *read* and compare the pictures. What was the colour of the bands and how were the details in both telescopes? What does PTV or L/xxx mean?
Clear sky,
Roland


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stanislas-jean
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Re: Jupiter in small refractor telescopes new [Re: Niklo]
      #6310425 - 01/13/14 02:42 PM

The sketch were done under seeing as noted, globally 1 step in favor to ED100 scope.
I have the feeling that under perfect images the apo will get only a little more but not small fine features in addition.
The Istar get globaly more defined feature contour and I feel it is possible to go deeper.
The overall image stays whitish in the achromat sothat (not on this report) but GRS get a deep orange color, NTB and STB get red violet colors to salmon, brownish on some area. The disk is not colored globally by a violet haze even at 171x.
The apo get also colors on features but rather pastel, the background color of the disk rather yellowish light. 150x was workable (not actually at 180x).
If you compare the details reported in EZ, the achromat get more in NTB and STB we get more also. The small contrasted details fade quicker with the seeing degradation.
My explanation about is to conclude on the lack of optical acuracy on the apo doublet in comparison with the Istar.
The Istar is Lambda/6 minimum, the TAL is L/4 may be 5, so that with the images got in the apo I expect L/4 probably less. The Tal get more into EZ and the NTB-STB bands with the comparison.
L/xx means lambda/ and PTV peak to valley expressed in Lambda/xxx.
I get this apo recently sothat Ididn't yet perform a roddier test on, but did in past on a second tube that I owned, equipped with the 53 glass with same observations on planet.
Sothat the discussion on chromatic aberration only as the proper indice for the ability of scopes is not enough but the optical acuracy has to be also considered.
The 2 sketch given illustrate this fact.
You may have a read on the de Suiter book "star testing astro. telescopes" for getting tendencies where a pure L/4 is sim