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What level of clarity should I expect when viewing Jupiter? 8" Orion Newtonian

beginner collimation planet
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#26 Redbetter

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Posted 20 March 2019 - 12:06 AM

While collimation is important, it is typically way overstressed in threads like this.  Yes, actual poor collimation will limit the level of detail, and make it difficult to get decent focus, but seeing is far more frequently a much larger factor.  Collimation won't matter much at all if the seeing is poor...which is the norm for many of us.  Collimation can be fair and still give decent detail, it just won't provide that last bit of crispness that precise collimation provides.  You can tell when the seeing is good if the collimation is holding you back.  I have seen the trade off in collimation and seeing issues with SCT, MCT, Dob, and refractors (yes, even refractors are prone to collimation/alignment issues at times.)

 

If collimation is the source of the problem, then it should be apparent in the image as well.  Turning to a bright star and racking focus back and forth will confirm if it is a collimation problem.

 

This thread started two months ago when Jupiter was lower in the morning sky, and it was likely very poorly placed for most observers.  Therefore, the seeing aspect is even greater, because seeing problems are often amplified many fold at low declinations.  And the thread was posted mid winter, when the seeing is typically at its worst.

 

~250x from an 8" Dob isn't asking all that much if the seeing is good and the planet is well enough placed in the sky.  My old 8" SCT without any fans does well at 300x in good seeing.  (I won't claim its collimation was historically "perfect", but after some initial fine tuning it held for well over a decade with virtually no tweaks.)  From what I have seen of Jupiter through our 10" Dob I would expect an 8" Dob to be good for somewhat over 300x if the optics are good and conditions support it.  I would expect it to have somewhat of an edge in planetary mag/inch compared to an SCT from what I have seen.



#27 miamichillin99

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Posted 27 March 2019 - 09:03 AM

Last night I did my best at fine tuning the collimation on my C8 using 500x. Under slight defocus I placed the Poission spot dead center of the bright ring. This morning I wake up at 5am to give Jupiter a test drive. Clear dark skies reported above average seeing and meteoblue a 4/5. I was excited. I drop in a Nagler 9mm and a 15mm. Focus on the moons. And after 30mins of trying really hard to see detail the most I could make out was the two bands, which actully looked more like one really fat band with darker edges and the GRS as a tiny red dot. I also couldnt make out any additional detail with the 9mm than I could with the 15mm. I even tried the 15mm with a 2.5x powermate and image was just very soft. Jupiter was at about 27 altitude. I guess this is normal from what Im reading here. I was hoping for more.

#28 vdog

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Posted 27 March 2019 - 11:33 AM

Last night I did my best at fine tuning the collimation on my C8 using 500x. Under slight defocus I placed the Poission spot dead center of the bright ring. This morning I wake up at 5am to give Jupiter a test drive. Clear dark skies reported above average seeing and meteoblue a 4/5. I was excited. I drop in a Nagler 9mm and a 15mm. Focus on the moons. And after 30mins of trying really hard to see detail the most I could make out was the two bands, which actully looked more like one really fat band with darker edges and the GRS as a tiny red dot. I also couldnt make out any additional detail with the 9mm than I could with the 15mm. I even tried the 15mm with a 2.5x powermate and image was just very soft. Jupiter was at about 27 altitude. I guess this is normal from what Im reading here. I was hoping for more.

I've found the seeing forecasts on cleardarksky to be like any other weather forecast:  hit or miss.  You don't know until you get outside and look what the seeing is going to be like.  With Jupiter, I start at 50x to see how much "ripple" is in the air and go from there.

 

I get the best view of Jupiter at about 220x (anything higher than that starts to get mushy), with two stacked filters (single polarizer on top, moon & skyglow on the bottom).  The polarizer cuts the glare and reduces diffraction spikes and halo; the M&SG increases contrast.

 

When the seeing is really bad, I've found a blue filter helps "mask" it and makes the bands and GRS (if in transit) stand out more.  I'll also go down in magnification (or give up entirely) if the seeing is just awful.

 

Time and patience are always required as I wait for periods of clarity in between the periods of atmospheric interference.  When they come, the views can be fleeting but breathtaking.


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#29 miamichillin99

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Posted 27 March 2019 - 11:40 AM

Thanks for tips on filters. I tried blue and did not notice any improvement. I do have a skyglow so I will try it out. Unfortunately I dont have a moon or polarizing filter. I do have a luminance that I use for astrophoto. Might try it too. I noticed very little ripple at low magnification but over 150x it began to be noticeable.

Edited by miamichillin99, 27 March 2019 - 11:42 AM.


#30 vdog

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Posted 27 March 2019 - 12:13 PM

Thanks for tips on filters. I tried blue and did not notice any improvement. I do have a skyglow so I will try it out. Unfortunately I dont have a moon or polarizing filter. I do have a luminance that I use for astrophoto. Might try it too. I noticed very little ripple at low magnification but over 150x it began to be noticeable.

For me, the blue doesn't enhance detail in the bands but just makes them stand out better against the lighter parts of Jupiter's atmosphere.  It's a noticeable but not dramatic effect and may not noticeable at all at lower magnifications.

 

The M&SG does enhance the band structure itself, revealing swirls and irregularities along the edges and enhancing the orange tones of the bands and GRS.  Again, though, not dramatically but noticeably and only at high magnifications.

 

A moon filter (like a 25% or 13%) is probably too dark for Jupiter anyway.  I only use my 13%ND on the moon, Venus, and Mars.

 

Keep trying and be patient.  Sometimes the seeing improves after sunrise and I'll stay out well into the morning before I pack it in.



#31 Special Ed

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Posted 27 March 2019 - 01:02 PM

miamichillin99,

 

Did you leave your scope out all night or did you bring it out of the house at 5 AM?  A C8 can take a while to reach equilibrium and tube currents can look like poor seeing.

 

Here's an example of what you can see with a C8.  The altitude was just a few degrees higher than what you report and the seeing and transparency were just average for this observation.  I generally observe Jupiter from a 160x to 250x magnification range.

 

Jupiter_Io_Transit_08.03.2009.v1.JPG

 

Here's another example.  I used green, orange, and yellow-green filters for this one.

 

Jupiter_05.21.2009.v1.JPG


Edited by Special Ed, 27 March 2019 - 01:06 PM.


#32 miamichillin99

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Posted 27 March 2019 - 07:59 PM

Hi Ed. Yes scope was out since 8pm the previous night when I collimated it. Left it out all night afterwards. Its truly amazing the detail you see. My equipment is a classic c8, orion aluminum coated diagonal, and the 9mm and 15mm Naglers. Collimated using Eds (another Ed) SCT collimation method and Bobs Knobs. I have never had the pleasure of seeing an airy disc with a diffraction ring so I collimate by defocusing to 2 tiny rings and center the poisson spot at 250x and then 500x.

Also from recent pics of Jupiter such as this:
https://www.astrobin.com/397361/

I can now see why it looked like one wide dark band with darker edges. The middle has become quite reddish lately.

Edited by miamichillin99, 27 March 2019 - 08:11 PM.


#33 kledward

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Posted 31 March 2019 - 08:11 PM

The software program in my signature will let you simulate the effect of the telescope's resolution on planetary details, a few screenshots are provided in the link if interested 

 

In an 8 inch you can start to see the fine details in the cloud bands in good seeing


Edited by kledward, 31 March 2019 - 08:13 PM.



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